The document discusses water pollution and freshwater treatment. It covers the hydrologic cycle and sources of fresh water. Various types of water pollution are described, including biodegradable organic substances, nutrients, pathogens, salinity, heavy metals, and thermal pollution. The document also discusses parameters for characterizing water quality, such as pH, alkalinity, hardness, and methods for measuring biochemical oxygen demand and chemical oxygen demand. Wastewater treatment methods including preliminary, primary, secondary and tertiary treatments are also outlined.

1. WATER POLLUTION
1. Introduction.
1.1. Need for water.
1.2. Location of water.
1.3. Hydrologic cycle.
2. Fresh water composition.
3. Fresh water pollution.
4. Natural regeneration.
5. Parameters determining water’s characteristics.
5.1. Physical parameters.
5.2. Chemicals Parameters.
5.3. Other parameters.
6. Legislation.
6.1. European Charter on Water Resources.
6.2. Spanish Legislation.
6.3. European Legislation.
7. Wastewater treatment.
7.1. Introduction.
7.2. Preliminary treatment.
7.3. Primary treatments.
7.4. Secondary treatments.
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2. 7.5. Tertiary treatments.
7.6. Effluent disinfection.
8. Sludge treatment.
8.1. Introduction.
8.2. Concentration.
8.3. Stabilization.
8.4. Mechanical dewatering
8.5. Heat drying.
8.6. Final disposal.
9. Examples of urban wastewater treatment
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3. 1. Introduction.
The four basic natural resources are water, air, land and energy. We need water for
multiple uses and a certain quality is required. Its use leads to the generation of
wastewater that can cause an impact on the environment.
Water scarcity and pollution has become of most importance in recent years. In
this chapter we’ll discuss both fresh water and wastewater treatment, either for reuse or
disposal in the environment "without polluting it"
1.1 Need for water.
The use of water could be classified in order of importance as shown in Table 1.
Table 1. Water use.
Needs WORLD WIDE % EUROPE %
Agriculture 66 30
Industry 24 14
Urban 8 18
Others (refrigeration, energy, 2 38
recreational, etc.)
Let's see some examples of the order of magnitude of water consumption:
Agriculture. In Spain, water consumption in agriculture makes up 80%, although
with modern techniques of drip irrigation, significant savings could be achieved. For
example, to produce 1 metric ton of maize 1,000 metric tons of water are needed.
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4. Industry. The applications of water in industry are numerous. For example, to
produce 1 ton of paper requires 25 metric tons of water and a tanning factory consumes
over 20 L of water per kilo of raw material
Domestic uses. In Spain each habitant consumes between 200 and 300 liters. An
American consumes about 340 litres per day.
As we can see, needs for water at home are minimal when compared to the overall
amount required by man to cover all their needs.
Information about water use in Europe can be found at
http://www.grid.unep.ch/product/publication/freshwater_europe/consumption.php
1.2 Location of water.
Water is one of the most abundant substances in nature. It is found in:
Living beings, as the main constituent.
In most foods.
On Earth. Water covers nearly three quarters of the earth's surface, with a total
volume of about 1,360 106 km3.
It is distributed as shown in Table 2:
4

5. Table 2. Water inventory.
Reservoir Volume (cubic km Percent of Total
x 1,000,000)
Oceans 1,370 97.25
Ice Caps and Glaciers 29 2.05
Groundwater 9.5 0.68
Lakes 0.125 0.01
Soil Moisture 0.065 0.005
Atmosphere 0.013 0.001
Streams and Rivers 0.0017 0.0001
Biosphere 0.0006 0.00004
This could be a pessimistic inventory of available water, given that nearly 98% is
sea water, and, almost 80% of the rest is ice. However, this is not a real picture because
the water available for consumption is renewed through the water cycle.
1.3 Hydrologic cycle.
Hydrologic cycle is the process by which the amount of water existing on earth
remains constant and is due to the constant exchange of water that takes place between
the earth's surface and atmosphere.
5

6. The hydrologic cycle is a conceptual model that describes the storage and
movement of water between the biosphere, atmosphere, lithosphere, (Figure 1), and the
hydrosphere. Water on this planet can be stored in any one of the following reservoirs:
atmosphere, oceans, lakes, rivers, soils, glaciers, snowfields, and groundwater.
Figure 1. Hydrologic cycle.
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7. Table 3. Typical residence times of water found in various reservoirs.
Reservoir Average Residence Time
Glaciers 20 to 100 years
Seasonal Snow Cover 2 to 6 months
Soil Moisture 1 to 2 months
Groundwater: Shallow 100 to 200 years
Groundwater: Deep 10,000 years
Lakes 50 to 100 years
Rivers 2 to 6 months
2. Fresh water composition.
Fresh water is not pure because of its high power as solvent. Thus, it contains
dissolved gases, suspended solids and dissolved solids. These compounds are
incorporated during its fall as rain and during its percolation through the soil. In
addition, water also incorporates microorganisms from air and soil.
Thus, groundwater presents a very high degree of mineralization, as opposed to
surface water. Table 3 compares the characteristics of groundwater and surface.
Table 4. Characteristics of surface and groundwater
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8. Characteristics surface water groundwater
Minerals Low High
Dissolved oxygen Saturated Low
Hydrogen sulphide Absent May be present
Colour Present Not present
Turbidity Present Not present
Iron and manganese Unusual Frequent
Organic Compounds Variable Variable
Pollution Frequent Unusual
3. Fresh water pollution.
Fresh water pollution is caused by the discharges of toxic substances coming from
domestic, industrial and agricultural uses. Water pollutants are classified as:
• Biodegradable Organic Substances. These are substances that oxidize in the
presence of oxygen due to bacterial activity. As a result, there is a decrease in the
concentration of dissolved oxygen, which causes:
Adverse effects on aquatic life.
Presence of bad odours.
• Nutrients. These are essential chemical elements for the growth of life. In
addition to carbon N, P, S, K, Ca, Fe, Mn, Co B are also needed.
Nutrients become pollutants when their concentrations are so high that they allow
excessive growth of aquatic plants, mainly algae. This process is called
eutrophication and is mainly due to an increase in phosphorus.
• Pathogens. Those organisms able to produce diseases.
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9. Examples of pathogens associated with water are viruses, bacteria, protozoa and
helminths.
• Salinity. The amount of dissolved salts limits the possible uses of water. It is
normally due to the presence of chloride.
Water is brackish when chloride content is greater than 5,000 ppm. Chloride
content in drinking water must be less than 500 ppm.
• Heavy metals. Among the heavy metals are: Al, As, Be, Bi, Cd, Zn, Co, Cu, Cr,
Sn, Fe, Mn, Hg, Ni, Pb, Se, Tl, Ti. Some of them are nutrients for many animals
and plants, but in greater concentrations they are toxic.
One characteristic of metal pollution is its persistence in the environment. In
addition, heavy metals concentrate along the food chain.
• Minor organic compounds. These compounds are found in a lesser
concentration and come from plastics, fuels, solvents, paints, pesticides,
detergents, food additives, pharmaceuticals, etc. Usually these compounds are
hardly biodegradable or non-biodegradable.
• Radioactive substances. Produced during the production and use of uranium.
However, some of the radioactive elements found in water are of natural origin.
• Thermal pollution. It is due to the use of water as coolant in many industrial
processes, when a large part of the water returned to its natural source returns
several degrees warmer. Increment of temperature causes the following effects:
Reduce oxygen solubility in water.
Increase metabolic reactions speed.
• Sediments. These are mixtures of mud, sand, organic matter and various
minerals, that appear as a result of erosion and domestic and industrial discharges.
Harmful effects of sediments are:
Reduce the capacity of lakes and reservoirs.
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10. Affect the bottom-dweller life.
Produce turbidity.
4. Natural regeneration.
When a discharge of domestic wastewater to a river occurs, microorganisms use
organic material to obtain energy through oxidation with the dissolved oxygen in water
(catabolism), as well as to construct cell-matter (anabolism).
This will cause the elimination of organic matter and a reduction of O2
concentration in water. As available food sources diminish, the death of microorganisms
and destruction of cell-material is produced. At the same time, oxygen concentration
increases due to its diffusion from atmosphere. At the end of this process, downstream,
the situation goes back to its initial state, through a natural regeneration process.
However, the capacity for this natural regeneration is limited, so that wastewater
should be treated before being discharged.
5. Parameters determining water’s characteristics.
5.1 Physical parameters.
• Temperature. It is measured easily and is very important in order to assess the
speed of biochemical reactions of organic matter decomposition, the solubility of
gases or amplification of flavors and odours.
• Color. It is due to the presence of organic and inorganic materials in water. True
color is due to dissolved materials and apparent color is due to suspended
materials. Color is usually measured by comparison with colored patterns.
• Turbidity. Water is cloudy when it contains material or colloidal suspension.
Turbidity can be determined by these methods:
10

11. a) Turbidimetry: Comparing the transmission of white light through the
suspension and through a standarized solution.
b) Nephelometry. Comparing the intensity of light scattered in the sample
and in a reference dissolution. This method is broadly used and can be
carried out continuously and is related to suspended solids.
Figure 2. Equipment for turbidity determination.
• Solids: Total solids refer to the residue remaining after a process of evaporation at
103-105 ° C.
Solids can be classified according to different criteria:
a) Depending on their nature.
Organic. These are substances of animal or vegetal origin containing C, H and
O, and they can be combined with N, S, P, etc. Major groups are proteins,
carbohydrates and fats, together with its decomposition products. Also called
volatile.
Inorganic. These are inert substances not subject to degradation. There are fuel
and ashes remaining at 550 ºC, although some salts decompose at lower
temperatures. One example is magnesium carbonate, which breaks down into
11

12. magnesium oxide and carbon dioxide at 350 ° C. Inorganic solids are also
known as minerals.
b) Depending on its size.
Dissolved. They pass through a filter. A fiberglass filter is generally used 0,45
μm. They can be classified as:
Colloidal (0,001 - 1 μm).
Not filtrables. They are suspended solids.
c) According to its settling. For this determination the sample is settling in a 1L
Imhoff cone for 1 hour, determining the volume of the settled sediments,
expressed as mL/L.
Not settling.
Figure 3. Equipment for suspended solids determination.
• Electrical conductivity. This value depends on the concentration of dissolved
salts. It is measured by a conductivity tester.
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13. Figure 4. Equipment for electrical conductivity determination.
5.2 Chemical Parameters.
• pH. It refers to the concentration of hydrogen ions in the sample. It is measured
with a pH meter. pH provides information on chemical reactions that can take
place and on the biological activity of the sample.
Figure 5. Equipment for pH determination.
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14. • Alkalinity and acidity. The alkalinity of water is a measure of its capacity to
neutralize acids. It is specifically defined as the amount of H+ ions that must be
added to a certain volume of water for that it reaches a certain pH. Thus can be
referred to Alkalinity to pH 8.2 (p-alkalinity) or Alkalinity to pH 4.3 (total
alkalinity or m-alkalinity)
Alkalinity is determined by titration with acid (H2SO4 generally or ClH).
When the pH reaches 8.2, hydroxides and carbonates are determined, as
species have become H2O and HCO3-. Total alkalinity is determined titrating
until HCO3 becomes CO2 and H2O.
Obviously, a pH 6.5 water will not present P-alkalinity, but total alkalinity.
Alkalinity is usually expressed in mg/l CaCO3 and is a measure of the capacity
of water to neutralize acids.
The concept of acidity is the opposite to alkalinity, thus the amount of OH-
ions that must be added to a certain volume of water to reach a certain value of
pH. We also distinguish between acidity pH 4.3 and pH 8.2.
• Hardness. Total hardness is given by the total content of calcium and
magnesium ions. For its numerical expression it is referred to calcium
carbonate or calcium oxide as parts per million (ppm) of calcium carbonate, ie
milligrams of calcium carbonate per litre.
There are two types of hardness:
Temporary. It is due to calcium and magnesium bicarbonate. It is eliminated
by boiling water when carbonate precipitates.
Permanent. It is the remaining after boiling the sample.
Total hardness is the sum of the two former.
• Oxidation/reduction potential. It is the potential required to transfer electrons
to a oxidizer from a reducer. It is measured with a potentiometer. This
parameter is used to control water treatment processes in which reduction-
14

15. oxidation reactions are involves, such as chlorination, nitrification-
denitrification, and so on.
• Organic matter. There are three parameters to determine the organic matter:
BOD5 (biochemical oxygen demand). It refers to the ppm of oxygen used by
the bacterial population in five days to degrade at a temperature of 20 ° C the
biodegradable organic matter present. This parameter is very important because
it indicates the quantity of O2 necessary to stabilize organic matter and is very
useful when designing a facility or determining the effectiveness of processes.
The biochemical oxidation is a slow process. In 20 days the oxidation of
organic matter comes at a 95-99%. At 5 days is 60 to 70%.
There are mainly two ways to conduct the determination of the BOD.
Dilution method
To ensure that all other conditions are equal, a very small amount of micro-
organism seed is added to each sample being tested. This seed is typically
generated by diluting activated sludge with de-ionized water. The BOD test
is carried out by diluting the sample with de-ionized water with added
nutrients, saturated with oxygen, inoculating it with a fixed aliquot of seed,
measuring the dissolved oxygen and sealing the sample (to prevent further
oxygen dissolving in). The sample is kept at 20 °C in the dark to prevent
photosynthesis (and thereby the addition of oxygen) for five days, and the
dissolved oxygen is measured again. The difference between the final DO and
initial DO is the BOD. The apparent BOD for the control is subtracted from
the control result to provide the corrected value.
The loss of dissolved oxygen in the sample, once corrections have been made
for the degree of dilution, is called the BOD5. For carbonaceous BOD (cBOD),
a nitrification inhibitor is added after the dilution water has been added to the
sample. The inhibitor hinders the oxidation of nitrogen. This inhibition allows
for measurement of carbonaceous oxygen demand (cBOD).
BOD can be calculated by:
15

16. Undiluted: Initial DO - Final DO = BOD
Diluted: ((Initial DO - Final DO)- BOD of Seed) x Dilution Factor
Manometric method
This method is limited to the measurement of the oxygen consumption due
only to carbonaceous oxidation. Ammonia oxidation is inhibited.
The sample is kept in a sealed container fitted with a pressure sensor. A
substance absorbing carbon dioxide (typically KOH) is added in the container
above the sample level. The sample is stored in conditions identical to the
dilution method. Oxygen is consumed and, as ammonia oxidation is inhibited,
carbon dioxide is released. The total amount of gas, thus the pressure,
decreases because carbon dioxide is absorbed. From the drop of pressure, the
electronics computes and displays the consumed quantity of oxygen.
The main advantage of this method compared to the dilution method is its
simplicity, thus no dilution of the sample, neither seeding, nor blank sample
are required. Besides a continuous and direct reading of BOD value is
displaied during the incubation time.
Furthermore, as the BOD measurement can be monitored continuously, a
graph of its evolution can be plotted. Interpolation of several graphs on a
similar water may build an experience of its usual evolution, and allow an
estimation of the five days BOD after as early as the first two days of
incubation.
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17. Figure 6. Equipment for BOD determination.
COD (chemical oxygen demand). COD is defined as the O2 ppm consumed
in the chemical oxidation of a sample of wastewater. Unlike the BOD, COD is
a measure of total organic matter. The COD can be considered as an
approximate measure of Theoretical Oxygen Demand. Depending on the
components of the sample, this approach will be better or worse. For example,
aromatic hydrocarbons and pyridine are not entirely oxidized, some very
volatile organic substances can escape through evaporation and oxidation can
occur of inorganic substances such as chloride (Cl-) and sulfides (S2-). The test
takes place in heating reflux conditions with a known amount of potassium
dichromate (K2Cr2O7). For the oxidation to be effective it must be done in an
acidic medium (adding H2SO4) and in the presence of a catalyst (Ag2SO4).
The reaction that takes place is the following:
Cr2O72- +14H+ + 6e- ↔2Cr3+ + 7 H2O
The measurement is carried out by assessing the remaining dichromate by
means of a titration with ammonium sulfate or ferrous spectrophotometric. To
cancel the interference of chloride, mercuric sulphate (HgSO4) is added, as the
17

18. mercury ion combines with the chloride ion to form mercuric chloride
(HgCl2), which is essentially non-ionized. This test takes just over two hours,
although techniques have been developed for roughly instrumental measuring
the COD within minutes.
Figure 7. Equipment for COD determination.
• TOC (total organic carbon). It is commonly used to determine small
concentrations of organic matter. This tests are based on organic matter carbon
oxidation to CO2, measuring absorption by KOH or by infrared analysis.
• Nitrogen. It is present in the form of organic nitrogen, ammonia, nitrites and
nitrates, which can transform from one to another through the process of
nitrification. Total Kjeldahl nitrogen (TKN) expresses the sum of organic
nitrogen and ammonia nitrogen . The relative concentrations of different forms
of nitrogen provide information on the degree of contamination of a sample.
• Phosphorus. It is present as phosphates from detergents and fertilizers. It is not
a direct risk to human or other lifeforms, but threatens water quality due to
eutrophication.
5.3 Other parameters.
In addition to the physical and chemical parameters, there are some others that
should be determined depending on the nature of the aqueous sample:
18

19. • Harmful chemicals: cyanides, sulphides, phenols, fats and oils, detergents,
pesticides, etc.
• Pathogenic organisms. Since they are present in very small quantities,
"indicator organisms” are needed, which are present in a greater quantity and
whose presence in water is related to the former ones. An example of these
indicator organisms are coliform bacteria.
• Parameters that describe the toxicity of a sample. There are some tests to
evaluate wastewater toxicity, which allows one to estimate the presence of
toxic substances. As examples of widely used tests the following can be cited:
AOX. It refers to the concentration in wastewater of substances absorbed in
active carbon.
METOX. It refers to the concentration of heavy metals. It is calculated as the
addition of the values resulting from multiplying certain heavy metals’
concentrations by a coefficient indicating their potential risks.
AOX and METOX express the concentration of certain toxic substances but
not the toxicity itself, however, their determination is easy to be carried out as
living organisms (that must be kept under certain conditions) are not required
and, moreover, these parameters are appropriate to compare the toxicity of
industrial wastewater (for example, METOX is often used to compare the
toxicity of wastewater from galvanic industries).
Inhibitor substances tests. They express toxicity as the interaction between
effluent and environment and are based in preparing various dilutions of
wastewater to find which concentration affects 50% of a population of
microorganisms, either by inhibiting some of its properties (EC50) or causing
its death (LC50). EC and LC are different from the ED and LD as the former
refers to concentrations (substance mg/L of wastewater, for example), while
the latter concern doses, ie, the weights of substances in an organism.
19

20. The organisms used to carry out these tests must be selected as representative
of the ecosystem, sensitive to small concentrations of toxic substances and easy
to handle. Daphnia (both Daphnia magna and Daphnia pulex) which is a micro
crustacean, is mainly used in wastewater toxicity tests, evaluating the
wastewater concentration that causes its inhibition or death, as well as
luminescent bacterium Photobacterium phosphoreum, determining its
luminescence loss when immersed in wastewater for 15 minutes. Lately most
tests are conducted with the latter method because of its ease of handling.
Toxicity is usually expressed in EQUITOX. An effluent presents N EQUITOX
when a N dilution factor sample causes the inhibition of 50% of Daphnia
population.
Figure 8. Equipment for toxicity determination.
The values of the most important parameters determining urban waste water
are detailed in Table 5.
20

21. Table 5. Parameters determining urban waste water
CONCENTRATION
PARAMETER (ppm) HIGH MEDIUM LOW
Total solids 1200 700 350
Suspended solids 350 200 100
BOD5 300 200 100
COD 1000 500 250
Total Nitrogen 85 40 20
Ammonia 50 25 12
Phosphorus 20 10 6
Fat 150 100 50
6. Legislation.
6.1. European Charter on Water Resources.
COUNCIL OF EUROPE COMMITTEE OF MINISTERS
Recommendation Rec (2001)14 Of the Committee of Ministers to member
states on the European Charter on Water Resources
(Adopted by the Committee of Ministers on 17 October 2001, at the 769th
meeting of the Ministers’ Deputies)
The Committee of Ministers,
Recalling its adoption of the European Water Charter on 26 May 1967;
Recalling its Decision No. CM/708/151298 to entrust the Committee for the
Activities of the Council of Europe in the field of Biological and Landscape
21

22. Diversity (CO-DBP) to look into the advisability of reviewing and updating the
European Water Charter;
Considering that water is indispensable to all forms of life;
Considering the importance of water in biological systems and the need to
protect aquatic and associated ecosystems, and soil in particular;
Considering that water is an ecological, economic and social asset that is a
prerequisite for sustainable development;
Considering that the preservation of water is the joint responsibility of states and
all users;
Considering that the increasing demand for water may lead to the deterioration
and exhaustion of water resources and conflicts between users, as well as
between states;
Considering that water management constitutes an ideal area for action by the
authorities in partnership with the various water users;
Having regard to the greater knowledge available and growing public and
government awareness since the adoption by the Council of Europe of the
European Water Charter on 6 May 1968;
Recalling the international instruments signed in this area, notably the Helsinki
Convention on the Protection and Use of Trans boundary Watercourses and
International Lakes of 17 March 1992, and the London Protocol on Water and
Health of 17 June 1999, chapter 18 of Agenda 21 adopted in Rio de Janeiro in
June 1992, the Sofia Convention on Co-operation for the Protection and
Sustainable Use of the Danube River of 29 June 1994, the New York
Convention on the Law of the Non-navigational Uses of International
Watercourses of 21 May 1997 and the Bern Convention on the Protection of the
Rhine of 12 April 1999;
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23. Recognizing that the Directive 2000/60/EC of the Council of the European
Union of 23 October 2000 incorporates many of the principles embedded in the
European Water Charter,
1. adopts the European Charter on Water Resources, which replaces the
European Water Charter proclaimed in Strasbourg on 6 May 1968;
2. recommends member states to take note of the charter and apply its principles
as appropriate in the framework of their national policies.
European Charter on Water Resources
1. Fresh water resources must be used in keeping with the objectives of
sustainable development, with due regard for the needs of present and future
generations.
Fresh water constitutes only 2.7% of the Earth’s overall water mass, and to a
large extent it is in a frozen state in the polar caps and the snow cover of high
mountains. Humanity uses more than half of the planet’s water reserves: the
quantity of water available per capita is now no more than 7 000 m3, as against
17 000 m3 as recently as 1950. At the same time, the world population is
growing, and water needs are increasing, not only for domestic use (currently
6% of world consumption), but also for industry (20%) and above all for
agriculture (70% to 80%).
Water is not only of vital importance for all forms of life, and thus for the
protection of the environment; its availability in sufficient quantity and quality is
also a prerequisite for the development of human societies. It is thus at the heart
of the concept of sustainable development, which brings together two
fundamental aspects of society: the need to protect the environment, and the
need to improve people’s living conditions. In 1987 this concept was defined as
development which meets the needs of present generations without
compromising the possibility for future generations of meeting theirs. 1
23

24. The International Court of Justice has summed up the situation as follows:
“[The] need to reconcile economic development with protection of the
environment is aptly expressed in the concept of sustainable development”. 2 The
objectives of sustainable development 3 include promoting economic growth and
improving social conditions, meeting essential needs, notably in terms of water,
and conserving and maintaining natural resources.
2. Water must be equitably and reasonably used in the public interest.
To determine what is equitable and reasonable, several factors must be
considered: geographic, hydrographic, hydrological, climatic and ecological
aspects; the economic and social needs of the populations concerned; the effects
of the utilization of the resource on other users and the need to conserve water,
harness water resources and avoid wastage, as well as the cost of measures taken
to this end. It is also important to consider alternatives to existing or planned
uses. All relevant factors are to be considered before reaching a conclusion, with
special regard being given to meeting vital human needs. 4
3. Water policy and law must protect the aquatic ecosystems and wetlands.
Water is an integral part of the ecosystem. It follows that water’s natural
function must be conserved, restored and enhanced. Hence the need to ensure
flow management that takes into account the natural flow of solid matter and
promotes interaction between the river, ground water and alluvial zones in their
capacity as natural flood zones. It is also necessary to conserve, restore and
improve natural habitats for wild fauna and flora in water, particularly in the
sediment and on riverbanks and lake shores, as well as in adjacent areas. The
natural movements of fish must be preserved. 5
4. It is up to everyone to help conserve water resources and use them prudently,
in conformity with this charter.
As in the case of the environment generally, responsibility for conserving water
resources cannot be regarded as being incumbent on the public authorities alone.
The 1968 Charter noted that as a consumer and user of water, each human being
24

25. is responsible to other users and that to use water thoughtlessly is to misuse the
natural heritage. 6
5. Everyone has the right to a sufficient quantity of water for his or her basic
needs.
International human rights instruments recognize the fundamental right of all
human beings to be free from hunger and to an adequate standard of living for
7
themselves and their families. It is quite clear that these two requirements
include the right to a minimum quantity of water of satisfactory quality from the
point of view of health and hygiene. 8
Social measures should be put in place to prevent the supply of water to destitute
persons from being cut off.
6. Public and private partners must introduce integrated management of surface
water, ground water and related water that respects the environment as a whole,
takes regional planning into account and is socially equitable and economically
rational.
Water management means planning the sustainable development of water
resources and providing for the implementation of any plans adopted. 9 These
operations must cover all expanses of fresh water, notably surface water and
ground water, and take quantitative and qualitative aspects into account. Their
objective must be to promote a dynamic, interactive and multi sector approach to
water management and utilization based on community needs and priorities. 10
Rational water utilization schemes for the development of surface and
underground water supply sources and other potential sources have to be
supported by concurrent water conservation and wastage minimization
measures. 11
7. Integrated management must be based on an inventory of water resources and
aim to ensure their protection, conservation and, if necessary, rehabilitation. In
particular, any new deterioration and exhaustion of these resources must be
prevented, the recycling of waste water encouraged and, where appropriate,
limitations placed on certain uses.
25

26. An inventory of water resources must include an assessment of their quantity
and quality, taking into account the requisite present and future uses as well as
the impact of foreseeable climate change. 12 Methods for the assessment of the
toxicity of hazardous substances and the noxiousness of pollutants which are or
might be discharged into water must be devised. Pollution from such substances
should be gradually reduced. Environmentally sound technologies, production
methods and consumption patterns must be developed and applied. 13
8. Water policy and law must be based on the principles of prevention,
precaution and correction at source as well as the “polluter-pays” principle. To
this end, they must use regulatory instruments such as quality objectives,
discharge standards, the best available technologies and economic instruments
compatible with meeting the population’s basic needs.
These principles have been formulated in international instruments and should
be applied to water resources in the following manner.
The principle of prevention means that the emission of pollutants must be
prevented, controlled and reduced at source through the application, in
particular, of low- and non-waste technology. The risk of accidental pollution
must be minimized and contingency planning developed. 14
The precautionary principle means that even in the absence of scientific
certainty, adequate measures must be taken to prevent qualitative or quantitative
deterioration of water resources when such deterioration might be serious or
irreversible.
Under the “polluter-pays” principle, the cost of pollution prevention, control and
reduction measures must be borne by the polluter.
Quality objectives determine the nature and quantity of pollutants acceptable in
water. They may depend on the utilization contemplated for a given aquatic
environment. Discharge standards define the maximum quantity of a given
pollutant that may be discharged into the aquatic environment.
The best available technology is taken to mean the latest stage of development
of processes, facilities or methods of operation which indicate the practical
26

27. suitability of a particular measure for limiting discharges, emissions and waste.
15
Legal instruments in the strict sense of the term include the impact study
procedure, which consists in requiring that, prior to implementation of a plan or
project, its environmental impact be studied, and that rules imposing an
obligation to obtain authorization for any activity that has a serious impact on
the environment as well as monitoring of authorized discharges be laid down. 16
Economic instruments may include such measures as taxation of pollutants, tax
relief on “clean” substances, quality seals certifying a product’s conformity with
the environmental protection requirement, the obligation to take out insurance
against environmental damage, negotiable authorization of pollutant emissions
and subsidies or loans. The latter must, however, be compatible with the
“polluter-pays” principle. All these instruments require a legal framework
specifying the standards and objectives to be complied with or attained.
In order to implement environmental protection measures, it is necessary to
identify and strengthen or develop, as required, the appropriate institutional,
legal and financial mechanisms. 17
9. Underground water resources must be the subject of special protection, and
their use for human consumption must take priority.
Ground water is usually connected with surface water and may be affected when
watercourses are modified. Its quality is usually such that it should be set aside
as far as possible for human consumption. Special measures must therefore be
adopted to protect ground water from pollution, whether as a consequence of
direct or indirect pollutants. 18 Ground water is particularly vulnerable to diffuse
pollution from manuring and deposits of pollutants that seep into it through the
soil. Preventive protection measures are needed, especially since the elimination
of pollutants that have seeped into the ground water may take years or even
decades.
10. Water resources must be regularly monitored and their general state
periodically assessed.
27

28. Programs must be devised and implemented to monitor the state of water. They
must provide for regular analyses to identify the causes of and parties
responsible for pollution. 19 . Such programs must also make it possible to check
whether the quality objectives have been attained as regards, in particular, the
health of the population concerned and the state of the ecosystems, and whether
safety measures to prevent accidents prejudicial to the quality or quantity of
water resources are functioning properly.
11. The terms of water concessions must be compatible with this charter.
Concessions must be granted for a limited duration and must be subject to
periodic review.
It is only fair that, as a counterpart to their rights and entitlements to water,
natural and legal persons and institutions, whether in the public sector or the
private sector, should contribute to the protection of the water environment and
the conservation of water resources. 20
To ensure better supervision of compliance with this obligation, it is essential for
such rights to be accorded for a limited duration only. Such limitation makes it
possible to modify the terms of the agreement granting the right to exploit the
water resources so as to take new data into account. At the same time, it
encourages beneficiaries to be more careful about honoring their obligations.
12. Large-scale consumption of water in agricultural or industrial processes must
be carefully assessed and monitored with a view to ensuring better protection of
the environment and avoiding unsustainable utilization.
The rapid increase in water needs makes it necessary to monitor constantly and
adjust, as appropriate, the allocation of water resources for different uses.
Reference should be made in this connection to the principles of sustainable
development and the equitable and reasonable use of water resources, cited
above. The holistic management of freshwater as a finite and vulnerable
resource, and the integration of sector water plans and programs into national
economic and social policy are of paramount importance. 21
28

29. 13. At each state level, central, regional and local authorities must adopt and
implement water management plans in a spirit of solidarity and co-operation.
These plans should be based on the catchment basin.
Integrated water resources management, including land-related aspects, should
be carried out at the level of the catchment basin or sub-basin. 22 This territorial
fragmentation of responsibilities should not, however, be an impediment to an
integrated water management policy at the level required. 23 A balance must be
struck between a spirit of solidarity and co-operation and the need to base action
on the dimensions of ecosystems, which usually coincide with those of
catchment basins.
14. Decisions on water must take into account the particular conditions at
regional or local level and be implemented by the relevant authorities closest to
the areas concerned in keeping with water management plans.
Whereas the utilization of water resources must be planned within the
framework defined in the previous paragraph, the implementation of directives
issued and decisions taken must be a matter for the local or regional authorities,
which are closer to the users. This means that more account can be taken not
only of the physical and ecological peculiarities of the various areas, but also of
the human aspects and economic and social conditions that characterize them.
15. States must co-operate, preferably within permanent institutions, to agree on
an equitable and reasonable method of managing international watercourses and
other shared water resources in conformity with international law and the
principles of this Charter.
States that share a catchment basin must conclude bilateral or multilateral
agreements specifying the geographic limits of their co-operation on the
management of shared water resources. They must take into consideration
requests concerning water transfers between catchment basins, and they must
work to establish permanent institutions to ensure better co-operation on the
management of shared water resources. These institutions can:
- collect, compile and evaluate data in order to identify pollution sources;
29

30. - elaborate joint water monitoring programs;
- draw up inventories and exchange information on pollution sources;
- set emissions limits for waste water;
- devise joint water quality objectives and criteria;
- serve as a consultation forum for the smooth functioning and maintenance of
facilities, installations and other structures associated with shared water
resources;
- develop action programs to reduce pollution loads;
- establish warning and alarm procedures. 24
16. The public must have access to information on the state of water resources.
The information collected on quantitative and qualitative aspects of water
resources, notably on suitability for drinking, must be accessible to the public
and published without delay in a form that is readily understandable. Provision
must be made for special warning measures to protect public health.
17. The public must be informed in a timely and appropriate manner of water
management plans and projects for the utilization of water resources. It has the
right to take an active part in planning and decision-making procedures
concerning water.
Access to information and participation by natural and legal persons and their
25
associations, organizations or groups in the decision-making process
concerning water resources are essential, in particular in order to enhance the
quality and the implementation of the decisions, to foster public awareness of
issues, to give the public the opportunity to express its concerns and to enable
public authorities to take due account of such concerns. 26
The authorities must make available to the public as soon as possible
information on water resources that is requested of them, including, if the
request is made, copies of documents in which such information is actually
30

31. recorded, without the public needing to advance a particular interest. A request
for information on water resources cannot be refused unless it concerns
documents in the course of being prepared or if it is contrary to the rights of
other persons protected by national legislation. Reasons for refusal must be
interpreted restrictively and must be communicated to those concerned. 27
The public must also be able to participate in preparing plans and programs on
water resources management at an appropriate stage. The relevant authority may
identify the persons invited to participate. Sufficient time-frames must be fixed
to allow for effective participation, and the public must be given the opportunity
to comment, directly or through representative consultative bodies. The result of
public participation shall be taken into account as far as possible. 28
18. The persons and bodies concerned must be able to appeal against any
decision relating to water resources.
Any natural or legal person wishing to contest any decision, act or omission and
in particular any refusal to provide information or allow participation in
connection with the management or utilization of water resources must be able
to lodge an administrative or judicial appeal. 29
19. Without prejudice to the right to water to meet basic needs, the supply of
water shall be subject to payment in order to cover financial costs associated
with the production and utilization of water resources.
Water has not only an ecological but also an economic value. In addition to
water as such, infrastructure for its extraction, conveyance, distribution and
purification generates costs which may vary from one place or community to
another, but which cannot be ignored. Water, costing nothing, might be used
wastefully, which is particularly dangerous in situations in which water
resources are becoming relatively scarce. On the other hand, water is also a
commodity with a social value, one that is necessary for meeting the basic needs
of every human being.
To finance the supply and purification of water, it is essential to implement the
“polluter-pays” principle. To this end, appropriate charges must bez set
31

32. (proportional or progressive rates, rates for low-income categories or supply of a
minimum quantity of water on preferential terms), depending on the use.
Charges will depend on the expected evolution of water resources, the
investment required and social considerations. The “user-pays” principle,
pursuant to which the price of water available for given uses – and thus of
adequate quality – must be borne by the user, must be taken into account,
subject to basic needs being met.
6.2. Spanish Legislation.
The Water Act, approved on 2 August of 1985 (Act 29/1.985), is the first to
comprehensively address the problem of water pollution in Spain. The development of
some titles of this law is carried out in the RD 1/2001, 20 July which approves the
regulation of public water domain.
These laws establish requirement to apply for official authorization for the
discharge of water and waste products that are likely to pollute the waters. The
authorisation granted by the administration lays down the conditions governing the
discharge:
• Limits of the discharge. Not exceeding the values given in Table 1 of Annex to
the IV title. These values are reflected in Table 6. Tables 2 and 3, require a higher
quality of discharge, and can be applied if necessary at any time by the Administration
depending on the point of discharge.
• Necessary wastewater treatment plants.
• Facilities operation control.
• Discharge fee according to section 105 of the Water Act.
• Construction dates.
• Emergency actions and measures.
32

33. Table 6. Discharge limits to reach.
PARÁMETER (ppm) TABLE 1 TABLE 2 TABLE 3
pH 5,5-9,5 5,5-9,5 5,5-9,5
Suspended solids 300 150 80
Settling solids 2 1 0,5
Coarse solids Ausentes Ausentes Ausentes
BOD5 300 60 40
COD 500 200 160
Color Inapreciable Inapreciable Inapreciable
Al 2 1 1
As 1,0 0,5 0,5
Ba 20 20 20
B 10 5 2
Cd 0,5 0,2 0,1
Cr (III) 4 3 2
Cr (VI) 0,5 0,2 0,2
Fe 10 3 2
Mn 10 3 2
Ni 10 3 2
Hg 0,1 0,05 0,05
Pb 0,5 0,2 0,2
Se 0,5 0,03 0,03
Sn 10 10 10
Cu 10 0,5 0,2
Zn 20 10 3
33

34. Article 105 of the Water Act stipulates that the discharge authorized in accordance
with the Articles 92 and following, are taxed with a fee to the protection and
improvement of the receiving environment of each river basin.
The fee is the result of multiplying the pollutant burden discharge C (expressed in
units of pollution) by the value assigned to each unit p.
Discharge fee
C=Cp
The unit of pollution is a standard measure pattern, that refers to the pollution load
through the discharge rate of domestic water for 1,000 inhabitants and in a one-year
period.
The burden discharge C is obtained as follows:.
C=K·V
Where V is the volume discharged in one year period m3/y and K is a coefficient
depending on the discharge characteristics
34

35. Table 7. K value ratio.
DISCHARGE k ACCORDING TO TREATMENT
CHARACTERISTICS
TABLE 1 TABLE 2 TABLE 3
1) Domestic
a) No industrial activity 1,0 0,20 0,10
b) Medium industrial activity 1,2 0,24 0,12
c) Important industrial activity 1,5 0,30 0,15
2) Industrial sector
a) Tye 1 2,0 0,40 0,20
b) Type 2 3,0 0,60 0,30
c) Type 3 4,0 0,80 0,40
Recently, many regional governments have developed laws on discharge
regulation, since their full attributions on environmental issues.
Thus, the Valencian region has a law for discharge, treatment and reuse of
wastewater since 1992 (Law 2 / 1992), introducing the concept of Sanitation Tax.
The Sanitation Tax for industrial use is calculated annually as follows:
Tax = (service fee + consumption fee) x corrective coefficient
35

36. The service fee depends on the size of the meter while the consumption fee’s
value resulting of multiplying the volume of water consumed by the water price of €/m3,
which is approved each year in the budget law.
The corrective coefficient fee is equal to the multiplication of 3 indexes, which
are:
• volume factor, which is a function of the annual balance of water used in
industry.
• peak factor, which is a function of the peak flows and pollution loads.
• corrective factor, depending on the value of certain wastewater characteristic
parameters.
6.3. European Legislation.
European legislation can be found at:
http://eur-lex.europa.eu/RECH_menu.do?ihmlang=en
The Council of Environment Ministers of the EEC adopted Directive
91/271/EC, on 21 May 1991, on urban waste water treatment.
It establishes the following:
• Definitions. p.e. (population equivalent)" means the organic biodegradable load
having a five-day biochemical oxygen demand (BOD5) of 60 g of oxygen per day.
• Regulations on sewage treatment, treatment in sensitive areas and less sensitive
areas, etc..
• Deadline for compliance with these regulations.
• Effect of wastewater from a member state over another.
36

37. • Regulations on industrial waste and sludge.
Text of the Directive 91/271/EC
COUNCIL DIRECTIVE
of 21 May 1991
concerning urban waste water treatment
(91/271/EEC)
THE COUNCIL OF THE EUROPEAN COMMUNITIES,
Having regard to the Treaty establishing the European Economic Community, and
in particular 130s thereof,
Having regard to the proposal from the Commission [1],
Having regard to the opinion of the European Parliament [2],
Having regard to the opinion of the Economic and Social Committee [3],
Whereas the Council Resolution of 28 June 1988 on the protection of the North
Sea and of other waters in the Community [4] invited the Commission to submit
proposals for measures required at Community level for the treatment of urban waste
water;
Whereas pollution due to insufficient treatment of waste water in one Member
State often influences other Member States' waters; whereas in accordance with Article
130r, action at Community level is necessary;
Whereas to prevent the environment from being adversely affected by the disposal
of insufficiently-treated urban waste water, there is a general need for secondary
treatment of urban waste water;
37

38. Whereas it is necessary in sensitive areas to require more stringent treatment;
whereas in some less sensitive areas a primary treatment could be considered
appropriate;
Whereas industrial waste water entering collecting systems as well as the
discharge of waste water and disposal of sludge from urban waste water treatment
plants should be subject to general rules or regulations and/or specific authorizations;
Whereas discharges from certain industrial sectors of biodegradable industrial
waste water not entering urban waste water treatment plants before discharge to
receiving waters should be subject to appropriate requirements;
Whereas the recycling of sludge arising from waste water treatment should be
encouraged; whereas the disposal of sludge to surface waters should be phased out;
Whereas it is necessary to monitor treatment plants, receiving waters and the
disposal of sludge to ensure that the environment is protected from the adverse effects
of the discharge of waste waters;
Whereas it is important to ensure that information on the disposal of waste water
and sludge is made available to the public in the form of periodic reports;
Whereas Member States should establish and present to the Commission national
programmes for the implementation of this Directive;
Whereas a Committee should be established to assist the Commission on matters
relating to the implementation of this Directive and to its adaptation to technical
progress,
HAS ADOPTED THIS DIRECTIVE:
Article 1
This Directive concerns the collection, treatment and discharge of urban waste
water and the treatment and discharge of waste water from certain industrial sectors.
The objective of the Directive is to protect the environment from the adverse
effects of the abovementioned waste water discharges.
38

39. Article 2
For the purpose of this Directive:
1. "urban waste water" means domestic waste water or the mixture of domestic
waste water with industrial waste water and/or run-off rain water;
2. "domestic waste water" means waste water from residential settlements and
services which originates predominantly from the human metabolism and from
household activities;
3. "industrial waste water" means any waste water which is discharged from
premises used for carrying on any trade or industry, other than domestic waste water
and run-off rain water;
4. "agglomeration" means an area where the population and/or economic activities
are sufficiently concentrated for urban waste water to be collected and conducted to an
urban waste water treatment plant or to a final discharge point;
5. "collecting system" means a system of conduits which collects and conducts
urban waste water;
6. "1 p.e. (population equivalent)" means the organic biodegradable load having a
five-day biochemical oxygen demand (BOD5) of 60 g of oxygen per day;
7. "primary treatment" means treatment of urban waste water by a physical and/or
chemical process involving settlement of suspended solids, or other processes in which
the BOD5 of the incoming waste water is reduced by at least 20 % before discharge and
the total suspended solids of the incoming waste water are reduced by at least 50 %;
8. "secondary treatment" means treatment of urban waste water by a process
generally involving biological treatment with a secondary settlement or other process in
which the requirements established in Table 1 of Annex I are respected;
9. "appropriate treatment" means treatment of urban waste water by any process
and/or disposal system which after discharge allows the receiving waters to meet the
relevant quality objectives and the relevant provisions of this and other Community
Directives;
39

40. 10. "Sludge" means residual sludge, whether treated or untreated, from urban
waste water treatment plants;
11. "eutrophication" means the enrichment of water by nutrients, especially
compounds of nitrogen and/or phosphorus, causing an accelerated growth of algae and
higher forms of plant life to produce an undesirable disturbance to the balance of
organisms present in the water and to the quality of the water concerned;
12. "estuary" means the transitional area at the mouth of a river between fresh-
water and coastal waters. Member States shall establish the outer (seaward) limits of
estuaries for the purposes of this Directive as part of the programme for implementation
in accordance with the provisions of Article 17 (1) and (2);
13. "coastal waters" means the waters outside the low-water line or the outer limit
of an estuary.
Article 3
1. Member States shall ensure that all agglomerations are provided with collecting
systems for urban waste water,
- at the latest by 31 December 2000 for those with a population equivalent (p.e.) of
more than 15000, and
- at the latest by 31 December 2005 for those with a p.e. of between 2000 and
15000.
For urban waste water discharging into receiving waters which are considered
"sensitive areas" as defined under Article 5, Member States shall ensure that collection
systems are provided at the latest by 31 December 1998 for agglomerations of more
than 10000 p.e.
Where the establishment of a collecting system is not justified either because it
would produce no environmental benefit or because it would involve excessive cost,
individual systems or other appropriate systems which achieve the same level of
environmental protection shall be used.
40

41. 2. Collecting systems described in paragraph 1 shall satisfy the requirements of
Annex I (A). These requirements may be amended in accordance with the procedure
laid down in Article 18.
Article 4
1. Member States shall ensure that urban waste water entering collecting systems
shall before discharge be subject to secondary treatment or an equivalent treatment as
follows:
- at the latest by 31 December 2000 for all discharges from agglomerations of
more than 15000 p.e.,
- at the latest by 31 December 2005 for all discharges from agglomerations of
between 10000 and 15000 p.e.,
- at the latest by 31 December 2005 for discharges to fresh-water and estuaries
from agglomerations of between 2000 and 10000 p.e.
2. Urban waste water discharges to waters situated in high mountain regions (over
1500 m above sea level) where it is difficult to apply an effective biological treatment
due to low temperatures may be subjected to treatment less stringent than that
prescribed in paragraph 1, provided that detailed studies indicate that such discharges do
not adversely affect the environment.
3. Discharges from urban waste water treatment plants described in paragraphs 1
and 2 shall satisfy the relevant requirements of Annex I.B. These requirements may be
amended in accordance with the procedure laid down in Article 18.
4. The load expressed in p.e. shall be calculated on the basis of the maximum
average weekly load entering the treatment plant during the year, excluding unusual
situations such as those due to heavy rain.
Article 5
1. For the purposes of paragraph 2, Member States shall by 31 December 1993
identify sensitive areas according to the criteria laid down in Annex II.
41

42. 2. Member States shall ensure that urban waste water entering collecting systems
shall before discharge into sensitive areas be subject to more stringent treatment than
that described in Article 4, by 31 December 1998 at the latest for all discharges from
agglomerations of more than 10000p.e.
3. Discharges from urban waste water treatment plants described in paragraph 2
shall satisfy the relevant requirements of Annex I B. These requirements may be
amended in accordance with the procedure laid down in Article 18.
4. Alternatively, requirements for individual plants set out in paragraphs 2 and 3
above need not apply in sensitive areas where it can be shown that the minimum
percentage of reduction of the overall load entering all urban waste water treatment
plants in that area is at least 75 % for total phosphorus and at least 75 % for total
nitrogen.
5. Discharges from urban waste water treatment plants which are situated in the
relevant catchment areas of sensitive areas and which contribute to the pollution of
these areas shall be subject to paragraphs 2, 3 and 4.
In cases where the above catchment areas are situated wholly or partly in another
Member State Article 9 shall apply.
6. Member States shall ensure that the identification of sensitive areas is reviewed
at intervals of no more than four years.
7. Member States shall ensure that areas identified as sensitive following review
under paragraph 6 shall within seven years meet the above requirements.
8. A Member State does not have to identify sensitive areas for the purpose of this
Directive if it implements the treatment established under paragraphs 2, 3 and 4 over all
its territory.
Article 6
1. For the purposes of paragraph 2, Member States may by 31 December 1993
identify less sensitive areas according to the criteria laid down in Annex II.
42

43. 2. Urban waste water discharges from agglomerations of between 10000 and
150000 p.e. to coastal waters and those from agglomerations of between 2000 and
10000 p.e. to estuaries situated in areas described in paragraph 1 may be subjected to
treatment less stringent than that prescribed in Article 4 providing that:
- such discharges receive at least primary treatment as defined in Article 2 (7) in
conformity with the control procedures laid down in Annex I D,
- comprehensive studies indicate that such discharges will not adversely affect the
environment.
Member States shall provide the Commission with all relevant information
concerning the abovementioned studies.
3. If the Commission considers that the conditions set out in paragraph 2 are not
met, it shall submit to the Council an appropriate proposal.
4. Member States shall ensure that the identification of less sensitive areas is
reviewed at intervals of not more than four years.
5. Member States shall ensure that areas no longer identified as less sensitive shall
within seven years meet the requirements of Articles 4 and 5 as appropriate.
Article 7
Member States shall ensure that, by 31 December 2005, urban waste water
entering collecting systems shall before discharge be subject to appropriate treatment as
defined in Article 2 (9) in the following cases:
- for discharges to fresh-water and estuaries from agglomerations of less than 2000
p.e.,
- for discharges to coastal waters from agglomerations of less than 10000 p.e.
Article 8
1. Member States may, in exceptional cases due to technical problems and for
geographically defined population groups, submit a special request to the Commission
for a longer period for complying with Article 4.
43

44. 2. This request, for which grounds msut be duly put forward, shall set out the
technical difficulties experienced and must propose an action programme with an
appropriate timetable to be undertaken to implement the objective of this Directive. This
timetable shall be included in the programme for implementation referred to in Article
17.
3. Only technical reasons can be accepted and the longer period referred to in
paragraph 1 may not extend beyond 31 December 2005.
4. The Commission shall examine this request and take appropriate measures in
accordance with the procedure laid down in Article 18.
5. In exceptional circumstances, when it can be demonstrated that more advanced
treatment will not produce any environmental benefits, discharges into less sensitive
areas of waste waters from agglomerations of more than 150000 p.e. may be subject to
the treatment provided for in Article 6 for waste water from agglomerations of between
10000 and 150000 p.e.
In such circumstances, Member States shall submit beforehand the relevant
documentation to the Commission. The Commission will examine the case and take
appropriate measures in accordance with the procedure laid down in Article 18.
Article 9
Where waters within the area of jurisdiction of a Member State are adversely
affected by discharges of urban waste water from another Member State, the Member
State whose waters are affected may notify the other Member State and the Commission
of the relevant facts.
The Member States concerned shall organize, where appropriate with the
Commission, the concertation necessary to identify the discharges in question and the
measures to be taken at source to protect the waters that are affected in order to ensure
conformity with the provisions of this Directive.
Article 10
44

45. Member States shall ensure that the urban waste water treatment plants built to
comply with the requirements of Articles 4, 5, 6 and 7 are designed, constructed,
operated and maintained to ensure sufficient performance under all normal local
climatic conditions. When designing the plants, seasonal variations of the load shall be
taken into account.
Article 11
1. Member States shall ensure that, before 31 December 1993, the discharge of
industrial waste water into collecting systems and urban waste water treatment plants is
subject to prior regulations and/or specific authorizations by the competent authority or
appropriate body.
2. Regulations and/or specific authorization shall satisfy the requirements of
Annex I C. These requirements may be amended in accordance with the procedure laid
down in Article 18.
3. Regulations and specific authorization shall be reviewed and if necessary
adapted at regular intervals.
Article 12
1. Treated waste water shall be reused whenever appropriate. Disposal routes shall
minimize the adverse effects on the environment.
2. Competent authorities or appropriate bodies shall ensure that the disposal of
waste water from urban waste water treatment plants is subject to prior regulations
and/or specific authorization.
3. Prior regulations and/or specific authorization of discharges from urban waste
water treatment plants made pursuant to paragraph 2 within agglomerations of 2000 to
10000 p.e. in the case of discharges to fresh waters and estuaries, and of 10000p.e. or
more in respect of all discharges, shall contain conditions to satisfy the relevant
requirements of Annex I B. These requirements may be amended in accordance with the
procedure laid down in Article 18.
45

46. 4. Regulations and/or authorization shall be reviewed and if necessary adapted at
regular intervals.
Article 13
1. Member States shall ensure that by 31 December 2000 biodegradable industrial
waste water from plants belonging to the industrial sectors listed in Annex III which
does not enter urban waste water treatment plants before discharge to receiving waters
shall before discharge respect conditions established in prior regulations and/or specific
authorization by the competent authority or appropriate body, in respect of all
discharges from plants representing 4000 p.e. or more.
2. By 31 December 1993 the competent authority or appropriate body in each
Member State shall set requirements appropriate to the nature of the industry concerned
for the discharge of such waste water.
3. The Commission shall carry out a comparison of the Member States'
requirements by 31 December 1994. It shall publish the results in a report and if
necessary make an appropriate proposal.
Article 14
1. Sludge arising from waste water treatment shall be re-used whenever
appropriate. Disposal routes shall minimize the adverse effects on the environment.
2. Competent authorities or appropriate bodies shall ensure that before 31
December 1998 the disposal of sludge from urban waste water treatment plants is
subject to general rules or registration or authorization.
3. Member States shall ensure that by 31 December 1998 the disposal of sludge to
surface waters by dumping from ships, by discharge from pipelines or by other means is
phased out.
4. Until the elimination of the forms of disposal mentioned in paragraph 3,
Member States shall ensure that the total amount of toxic, persistent or bioaccumulable
materials in sludge disposed of to surface waters is licensed for disposal and
progressively reduced.
46

47. Article 15
1. Competent authorities or appropriate bodies shall monitor:
- discharges from urban waste water treatment plants to verify compliance with
the requirements of Annex I.B in accordance with the control procedures laid down in
Annex I.D,
- amounts and composition of sludge disposed of to surface waters.
2. Competent authorities or appropriate bodies shall monitor waters subject to
discharges from urban waste water treatment plants and direct discharges as described
in Article 13 in cases where it can be expected that the receiving environment will be
significantly affected.
3. In the case of a discharge subject to the provisions of Article 6 and in the case
of disposal of sludge to surface waters, Member States shall monitor and carry out any
other relevant studies to verify that the discharge or disposal does not adversely affect
the environment.
4. Information collected by competent authorities or appropriate bodies in
complying with paragraphs 1, 2 and 3 shall be retained in the Member State and made
available to the Commission within six months of receipt of a request.
5. Guidelines on the monitoring referred to in paragraphs 1, 2 and 3 may be
formulated in accordance with the procedure laid down in Article 18.
Article 16
Without prejudice to the implementation of the provisions of Council Directive
90/313/EEC of 7 June 1990 on the freedom of access to information on the environment
[5], Member States shall ensure that every two years the relevant authorities or bodies
publish situation reports on the disposal of urban waste water and sludge in their areas.
These reports shall be transmitted to the Commission by the Member States as soon as
they are published.
Article 17
47

48. 1. Member States shall by 31 December 1993 establish a programme for the
implementation of this Directive.
2. Member States shall by 30 June 1994 provide the Commission with information
on the programme.
3. Member States shall, if necessary, provide the Commission by 30 June every
two years with an update of the information described in paragraph 2.
4. The methods and formats to be adopted for reporting on the national
programmes shall be determined in accordance with the procedure laid down in Article
18. Any amendments to these methods and formats shall be adopted in accordance with
the same procedure.
5. The Commission shall every two years review and assess the information
received pursuant to paragraphs 2 and 3 above and publish a report thereon.
Article 18
1. The Commission shall be assisted by a Committee composed of the
representatives of the Member States and chaired by the representative of the
Commission.
2. The representative of the Commission shall submit to the committee a draft of
the measures to be taken. The committee shall deliver its opinion on the draft within a
time limit which the chairman may lay down according to the urgency of the matter.
The opinion shall be delivered by the majority laid down in Article 148 (2) of the Treaty
in the case of decisions which the Council is required to adopt on a proposal from the
Commission. The votes of the representatives of the Member States within the
committee shall be weighted in the manner set out in that Article. The chairman shall
not vote.
3. (a) The Commission shall adopt the measures envisaged if they are in
accordance with the opinion of the committee.
(b) If the measures envisaged are not in accordance with the opinion of the
committee, or if no opinion is delivered, the Commission shall, without delay, submit to
48

49. the Council a proposal relating to the measures to be taken. The Council shall act by a
qualified majority.
If, on the expiry of a period of three months from the date of referral to the
Council, the Council has not acted, the proposed measures shall be adopted by the
Commission, save where the Council has decided against the said measures by a simple
majority.
Article 19
1. Member States shall bring into force the laws, regulations and administrative
provisions necessary to comply with this Directive no later than 30 June 1993. They
shall forthwith inform the Commission thereof.
2. When Member States adopt the measures referred to in paragraph 1, they shall
contain a reference to this Directive or shall be accompanied by such a reference on the
occasion of their official publication. The methods of making such a reference shall be
laid down by the Member States.
3. Member States shall communicate to the Commission the texts of the main
provisions of national law which they adopt in the field governed by this Directive.
Article 20
This Directive is addressed to the Member States.
Done at Brussels, 21 May 1991. For the Council. The President. R. STEICHEN
Annex I
REQUIREMENTS FOR URBAN WASTE WATER
A. Collecting systems (1)
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50. Collecting systems shall take into account waste water treatment requirements. The
design, construction and maintenance of collecting systems shall be undertaken in
accordance with the best technical knowledge not entailing excessive costs, notably
regarding:
• volume and characteristics of urban waste water,
• prevention of leaks,
• limitation of pollution of receiving waters due to storm water overflows.
B. Discharge from urban waste water treatment plants to receiving waters (1)
1. Waste water treatment plants shall be designed or modified so that
representative samples of the incoming waste water and of treated effluent can
be obtained before discharge to receiving waters.
2. Discharges from urban waste water treatment plants subject to treatment in
accordance with Articles 4 and 5 shall meet the requirements shown in Table 1.
3. Discharges from urban waste water treatment plants to those sensitive areas
which are subject to eutrophication as identified in Annex II.A (a) shall in
addition meet the requirements shown in Table 2 of this Annex.
4. More stringent requirements than those shown in Table 1 and/or Table 2 shall
be applied where required to ensure that the receiving waters satisfy any other
relevant Directives.
5. The points of discharge of urban waste water shall be chosen, as far as possible,
so as to minimize the effects on receiving waters.
C. Industrial waste water
Industrial waste water entering collecting systems and urban waste water treatment
plants shall be subject to such pre-treatment as is required in order to:
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51. • protect the health of staff working in collecting systems and treatment plants,
• ensure that collecting systems, waste water treatment plants and associated
equipment are not damaged,
• ensure that the operation of the waste water treatment plant and the treatment of
sludge are not impeded,
• ensure that discharges from the treatment plants do not adversely affect the
environment, or prevent receiving water from complying with other Community
Directives,
• ensure that sludge can be disposed of safety in an environmentally acceptable
manner.
D. Reference methods for monitoring and evaluation of results
1. Member States shall ensure that a monitoring method is applied which
corresponds at least with the level of requirements described below. Alternative
methods to those mentioned in paragraphs 2, 3 and 4 may be used provided that
it can be demonstrated that equivalent results are obtained. Member States shall
provide the Commission with all relevant information concerning the applied
method. If the Commission considers that the conditions set out in paragraphs 2,
3 and 4 are not met, it will submit an appropriate proposal to the Council.
2. Flow-proportional or time-based 24-hour samples shall be collected at the same
well-defined point in the outlet and if necessary in the inlet of the treatment
plant in order to monitor compliance with the requirements for discharged
waste water laid down in this Directive. Good international laboratory practices
aiming at minimizing the degradation of samples between collection and
analysis shall be applied.
3. The minimum annual number of samples shall be determined according to the
size of the treatment plant and be collected at regular intervals during the year:
- 2 000 to 9 999 p. e.: 12 samples during the first year. four samples in
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52. subsequent years, if it can be shown that the water during the first year complies
with the provisions of the Directive; if one sample of the four fails, 12 samples
must be taken in the year that follows. - 10 000 to 49 999 p. e.: 12 samples. - 50
000 p. e. or over: 24 samples.
4. The treated waste water shall be assumed to conform to the relevant parameters
if, for each relevant parameter considered individually, samples of the water
show that it complies with the relevant parametric value in the following way:
(a) for the parameters specified in Table 1 and Article 2 (7), a maximum number
of samples which are allowed to fail the requirements, expressed in
concentrations and/or percentage reductions in Table 1 and Article 2 (7), is
specified in Table 3; (b) for the parameters of Table 1 expressed in
concentrations, the failing samples taken under normal operating conditions
must not deviate from the parametric values by more than 100 %. For the
parametric values in concentration relating to total suspended solids deviations
of up to 150 % may be accepted; (c) for those parameters specified in Table 2
the annual mean of the samples for each parameter shall conform to the relevant
parametric values.
5. Extreme values for the water quality in question shall not be taken into
consideration when they are the result of unusual situations such as those due to
heavy rain.
(1) Given that it is not possible in practice to construct collecting systems and
treatment plants in a way such that all waste water can be treated during
situations such as unusually heavy rainfall, Member States shall decide on
measures to limit pollution from storm water overflows. Such measures could be
based on dilution rates or capacity in relation to dry weather flow, or could
specify a certain acceptable number of overflows per year.
Table 1:
Requirements for discharges from urban waste water treatment plants subject
to Articles 4 and 5 of the Directive. The values for concentration or for the
percentage of reduction shall apply.
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53. Parameters Concentration Minimum Reference method of
percentage of measurement
reduction (1)
Biochemical 25 mg/l O2 70-90 Homogenized, unfiltered,
oxygen demand undecanted sample.
(BOD5 at 20 40 under Determination of
°C) without dissolved oxygen before
nitrification (2) Article 4 (2) and after five-day
incubation at 20 °C ± 1
°C, in complete darkness.
Addition of a nitrification
inhibitor
Chemical 125 mg/l O2 75 Homogenized, unfiltered,
oxygen demand undecanted sample
(COD) Potassium dichromate
Total 35 mg/l 90 (3) - Filtering of a
suspended representative sample
solids 35 under 90 under through a 0,45 ìm filter
membrane. Drying at 105
Article 4 (2) Article 4 (2) °C and weighing
(more than 10 000 (more than 10 - Centrifuging of a
p.e.) 000 p.e.) representative sample (for
at least five mins with
60 under 70 under mean acceleration of 2
800 to 3 200 g), drying at
Article 4 (2) Article 4 (2)
105 °C and weighing
(2 000-10 000 p.e.) (2 000-10 000
p.e.)
(1) Reduction in relation to the load of the influent.
(2) The parameter can be replaced by another parameter: total organic carbon
(TOC) or total oxygen demand (TOD) if a relationship can be established
between BOD5 and the substitute parameter.
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54. (3) This requirement is optional. Analyses concerning discharges from
lagooning shall be carried out on filtered samples; however, the concentration
of total suspended solids in unfiltered water samples shall not exceed 150 mg/l.
Table 2:
Requirements for discharges from urban waste water treatment plants to
sensitive areas which are subject to eutrophication as identified in Annex II.A
(a). One or both parameters may be applied depending on the local situation.
The values for concentration or for the percentage of reduction shall apply.
Parameters Concentration Minimum Reference method of
percentage measurement
of reduction
(1)
Total phosphorus 2 mg/l P 80 Molecular
(10 000 - 100 000 p. e.) absorption
spectrophotometry
1 mg/l P
(more than
100 000 p. e.)
Total nitrogen (2) 15 mg/l N 70-80 Molecular
absorption
(10 000 - 100 000 p. e.) spectrophotometry
10 mg/l N
(more than
100 000 p. e.) (3)
(1) Reduction in relation to the load of the influent.
(2) Total nitrogen means: the sum of total Kjeldahl-nitrogen (organic N + NH3),
nitrate (NO3)-nitrogen and nitrite (NO2)-nitrogen.
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55. (3) Alternatively, the daily average must not exceed 20 mg/l N. This requirement
refers to a water temperature of 12° C or more during the operation of the
biological reactor of the waste water treatment plant. As a substitute for the
condition concerning the temperature, it is possible to apply a limited time of
operation, which takes into account the regional climatic conditions. This
alternative applies if it can be shown that paragraph 1 of Annex I.D is fulfilled.
Table 3 :
Series of samples taken in any year Maximum permitted number of samples
which fail to conform
4-7 1
8-16 2
17-28 3
29-40 4
41-53 5
54-67 6
68-81 7
82-95 8
96-110 9
111-125 10
126-140 11
141-155 12
156-171 13
172-187 14
188-203 15
204-219 16
220-235 17
236-251 18
252-268 19
269-284 20
285-300 21
301-317 22
318-334 23
335-350 24
351-365 25
Annex II.CRITERIA FOR IDENTIFICATION OF SENSITIVE AND LESS
SENSITIVE AREAS
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56. A. Sensitive areas A water body must be identified as a sensitive area if it falls
into one of the following groups:
(a) natural freshwater lakes, other freshwater bodies, estuaries and coastal
waters which are found to be eutrophic or which in the near future may
become eutrophic if protective action is not taken.
The following elements might be taken into account when considering which
nutrient should be reduced by further treatment:
(i) lakes and streams reaching lakes/reservoirs/closed bays which are
found to have a poor water exchange, whereby accumulation may take
place. In these areas, the removal of phosphorus should be included
unless it can be demonstrated that the removal will have no effect on
the level of eutrophication. Where discharges from large
agglomerations are made, the removal of nitrogen may also be
considered;
(ii) estuaries, bays and other coastal waters which are found to have a
poor water exchange, or which receive large quantities of nutrients.
Discharges from small agglomerations are usually of minor importance
in those areas, but for large agglomerations, the removal of phosphorus
and/or nitrogen should be included unless it can be demonstrated that
the removal will have no effect on the level of eutrophication;
(b) surface freshwaters intended for the abstraction of drinking water which
could contain more than the concentration of nitrate laid down under the
relevant provisions of Council Directive 75/440/EEC of 16 June 1975
concerning the quality required of surface water intended for the abstraction
of drinking water in the Member States (1) if action is not taken;
(c) areas where further treatment than that prescribed in Article 4 of this
Directive is necessary to fulfill Council Directives.
(1) OJ No L 194, 25. 7. 1975, p. 26 as amended by Directive 79/869/EEC (OJ
No L 271, 29. 10. 1979, p. 44).
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57. B. Less sensitive areas A marine water body or area can be identified as a less
sensitive area if the discharge of waste water does not adversely affect the
environment as a result of morphology, hydrology or specific hydraulic
conditions which exist in that area. When identifying less sensitive areas,
Member States shall take into account the risk that the discharged load may be
transferred to adjacent areas where it can cause detrimental environmental
effects. Member States shall recognize the presence of sensitive areas outside
their national jurisdiction. The following elements shall be taken into
consideration when identifying less sensitive areas: open bays, estuaries and
other coastal waters with a good water exchange and not subject to
eutrophication or oxygen depletion or which are considered unlikely to become
eutrophic or to develop oxygen depletion due to the discharge of urban waste
water.
Annex III
INDUSTRIAL SECTORS
1. Milk-processing
2. Manufacture of fruit and vegetable products
3. Manufacture and bottling of soft drinks
4. Potato-processing
5. Meat industry
6. Breweries
7. Production of alcohol and alcoholic beverages
8. Manufacture of animal feed from plant products
9. Manufacture of gelatine and of glue from hides, skin and bones
10. Malt-houses
11. Fish-processing industry
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58. 7. Wastewater treatment.
Wastewater treatment plant (WWTP) can receive:
• Domestic Wastewater from residential areas or commercial facilities.
• Industrial wastewater.
• Uncontrolled contributions to a public sewer.
• Rainwater, resulting from surface runoff.
A WWTP is designed to treat a certain flow. In case of a flow peak exceeding the
WWTP capacity, excess flow can’t be treated as influent and so it should be bypassed.
Once at the WWTP, wastewater must be pumped to overcome the head loss of the
different stages. Centrifugal pumps are commonly used (Figure 9 a) as well as
Archimedes screws. (Figure 9 b)
Figure 9 a. Centrifugal pump. Quart Benager WWTP (Valencia).
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59. Figure 9 b. Archimedes screws. Quart Benager WWTP (Valencia)
Sewage treatments depends on:
• Wastewater pollution degree (as characterization parameters seen above).
• The quality of treated wastewater (effluent) to achieve.
Wastewater treatments are the following:
• Preliminary treatment.
• Primary treatment.
• Secondary treatments.
• Tertiary treatment.
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60. Figure 10. General view of Quart Benager WWPT (Valencia).
7.1. Preliminary treatment.
Preliminary treatments remove solids, coarse materials, grit, sand, fats, etc, with a
dual objective:
• Reduction of wastewater pollution.
• Protection of the following treatment stages.
Processes found in a preliminary treatment.
Their function is to protect the plant, removing large objects that could cause
clogging and materials that can cause abrasion. The elimination of these substances is
achieved by making water pass through gates or sieves.
Coarse screens are classified as either bar racks or bar screens depending on the
spacing between the bars. Both consist of vertical arrangement or equally spaced
parallel bars designed to trap debris.
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61. • Bar racks. They are made of steel, usually inclined about 60-80 º on the
horizontal. This treatment effectiveness depends on the spacing between the bars, and it
ranges approximately from 50 mm to 100 mm. Cleaning can be manual or automatic.
Manual cleaning is done with a rake, while automatic cleaning can be done for example
with a swivel arm.
•. Bar screens. They are made of stainless steel. Spacing ranges between 6 mm to
50 mm.
•. Fine screens and sieves . They are made of stainless steel and can be classified
as rotary, vibrating, band, discs, stationary, etc. Opening ranges between 1 mm to 5 mm.
Figure 11. Automatic screening equipment
B. Grit removal systems. Wastewater grit materials ate generally non putrescible,
have a settling velocity greater than that of organic materials, and consist of discrete
particles. Such materials include sand, cinders, etc.
A grit removal system consists of a wide canal, so that water velocity decreases
allowing the deposition of sand. In the case of sewage it is difficult to prevent the settled
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62. sand from retaining organic matter so that a water speed in the channel of about 0.3 m/s
is needed, to allow low-density solids remain suspended and sand to settle.
C. Floatable solids removal.
Grease, oil, wax, scum, etc have to be removed because these substances hinder
air from dissolving into water. The process of elimination based on these materials are
less dense than water, thus tend to rise to the surface through natural waterline.
According to the above mentioned, reducing flow speed, acts as a separation.
Skimming process is achieved by surface collection and removal of these substances by
dumping or scraping.
Figure 12. Grit and sand removal stage.
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63. 7.2. Primary treatment.
The primary goal of primary treatment is solids removal by means of settling. In
some cases chemicals as coagulants and flocculants are used to increase colloidal
particles settling velocity, (physical-chemical treatment).
Among the primary treatments are:
A. Sedimentation. A sedimentation tank or clarifier is usually circular though may
be rectangular. Sludge settles when the speed of water is less than the speed of falling
particles.
The decanters can be static or dynamic.
• Static. There are no moving parts for the withdrawal of sludge or floating
materials. Used to treat low flows therefore have a small size, with a sloped bottom for
sludge to be discharged continuously. Shape is usually conical-cylinder. Some are
equipped with some elements, lamellae, usually metal or plastic, which help particles
settling.
• Dynamic. Equipped with electromechanical devices to collect both, floating
(scum) and settling (sludge) materials. Used to treat large flows, are the most common
in WWTP. According to its geometry are classified into rectangular and circular, the
latter being the most widely used.
Figure 13. Primary clarifier.
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64. B. Coagulation-flocculation. This process is used to remove heavy metals or
colloids present in wastewater. Coagulation destabilizes colloidal particles through the
neutralization of their electrical charges. This neutralization is achieved by adding a
coagulant, normally a metallic salt. Aluminium or iron salts are mainly used as
coagulants: i.e. aluminium sulfate, ferric chloride, ferric sulphate and ferrous sulfate.
Flocculation: After coagulation takes place flocculation is possible to achieve.
When particles are not electrically charged, they can form bigger particles, or floccs,
which can be removed by filtration, settling or flotation.
The coagulant, breaks the stability of colloids, which allows forming floccs, but it
is necessary to increase its volume, weight and cohesion. This is achieved through:
• Recycling sludge.
• Uniform and slow stirring.
• Using flocculants. They are used so-called polyelectrolytes, which are polymeric
compounds that make a link to separate particles.
C. Flotation. Used to remove suspended solids with a lower density than that of
water, as well as oils and fats. Flotation may be natural or induced. The latter consists of
setting artificial bubbles of air or gas on the particles to be eliminated.
There are three systems to produce and introduce air bubbles:
• aeration at atmospheric pressure. It consists of directly introducing small air
bubbles by diffusers at the bottom of the flotation tank.
• dissolved air flotation. It involves air saturated water at a pressure of 3 or 4 atm,
which when returning to the tank at atmospheric pressure, produces large amount of
small bubbles. Normally, the water used is part of the flotation effluent, returned to the
treatment.
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65. • vacuum flotation. In this case wastewater is saturated with air and then under the
action of vacuum. Under these conditions the solubility of gas in the fluid decreases,
forming large amounts of bubbles.
D. Equalizing tanks. Used to uniform properties of wastewater, flow, organic load,
et., as well as to neutralize when necessary (in case of biological treatment, etc.).
Common substances used to neutralize are caustic soda, lime, limestone, sulphuric acid
and CO2. Others include: nitric acid, hydrochloric acid, sodium carbonate and ammonia.
F. Other treatments..
Two treatments are included within the primary treatment, as they remove solid
sediments. The difference with the abovementioned treatments is that in sludge
anaerobic digestion takes place.
This process takes place in the Imhoff tanks and septic tanks.
• Imhoff Tanks. This is a tank divided into an upper compartment for
sedimentation, and a lower for sludge digestion. The use of Imhoff tanks is currently
limited to small plants.
• septic tanks. They consist of two or more chambers in series, so that the first
compartment is used for sedimentation, sludge digestion and storage, while the second
provides a sedimentation compartment and additional storage capacity.
These methods are used for the treatment of sewage from individual residences
and small communities. These techniques have fallen into disuse, under existing
regulations, since efficiency achieved is very low. Thus, the septic tank is only used in
compact WWTP as a first step, or preliminary treatment.
7.3. Secondary treatments.
The objective is to eliminate biodegradable organic matter by biological treatment.
Microorganisms are responsible for removing organic matter from wastewater, using
energy obtained from the oxidation of this, to carry out the processes of synthesis of
cellular material.
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66. Elimination of BOD is therefore achieved. An initial classification of these
processes can be established depending on the use or not of O2. In the first case we refer
to aerobic processes, while in the second to anaerobic processes.
Anaerobic processes are not enough in order to accomplish the quality needed to
discharge, so they are used as a first step in a biological treatment with an aerobic
process included.
Secondary treatments are listed below.
A. Activated sludge. This process consists of a population of aerobic microorganisms
dispersed in the aeration tank, stirred and aerated, and fed with wastewater or discharge
from primary treatment. The aeration provides oxygen for aerobic degradation of
aerobically degrading organic matter into carbon dioxide, water, new cells, and other
end products. After an appropriate retention time, the active sludge is discharged into
the secondary clarifier, where treated water is separated from the sludge.
Figure 15 Secondary clarifier.
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67. The settled sludge is recycled back to the aeration tank where organic matter
stabilization occurs, to maintain an appropriate concentration of bacteria in the aeration
tank, and a part, excess sludge, is removed to the sludge treatment line.
Depending on design, aeration tanks may be completely mixed or plug flow.
Design parameters are based on food/microorganisms ratio in the system. Other
important parameters to consider are O2 needed and nutrients, as well as excess sludge
production, which must be managed.
The two most common types of aeration systems used to supply O2 are subsurface
diffusion and mechanical aeration.
Porous diffusers and mechanical blowers are used to introduce air near the tank
bottom. Mechanical aerators use blades to agitate the tank’s surface and disperse air into
the mixed liquor, causing an increase of water-air interface thus promoting the exchange
of O2.
Figure 16. Aeration tank.
Pure O2 is also used. In this case the aeration tanks are usually covered, and the
oxygen is retuned, reducing the oxygenation requirements. This process must vent a
portion of the gas accumulated inside the aeration tank.
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68. Figure 17. Scheme of a WWPT.
B. Trickling filters
A trickling filter is an attached-growth, biological process that uses an inert
medium to attract microorganisms, which form a film on the medium surface.
A rotary or stationary distribution mechanism distributes wastewater from the top
of the filter percolating it through the interstices of the film-covered medium. As the
wastewater moves through the filter, the organic matter is absorbed onto the biofilm and
degraded by a mixed population of aerobic microorganisms.
The oxygen required for organic degradation is supplied by air circulating through
the filter induced by natural draft or ventilation.
One main difference with activated sludge processes, is that sludge is not returned
to the system, and excess sludge, detached from the biofilm is discharged with the
effluent.
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69. Figure 18. General view of a trickling filter.
C. Rotating contactors.
A rotating biological contactor (RBC) is an attached growth, biological process
that consists of a basin(s) in which large, closely spaced, circular disks mounted on
horizontal shafts rotate slowly through wastewater.
These discs are partially submerged in water, so that when turning get in contact
with air and water. Thus, when in contact with water, organic matter is adsorbed on the
biological film that grows on the disks and when in contact with air, absorb oxygen
necessary for aerobic process.
Figure 19. View of a rotating contactor.
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70. D. Fluidized bed reactors
A fluidized bed reactor is a combination of the most common stirred tank packed
bed, continuous flow reactors. It is very important to chemical engineering because of
its excellent heat and mass transfer characteristics. In a fluidized bed reactor, the
substrate is passed upward through the immobilized enzyme bed at a high velocity to
lift the particles. However the velocity must not be so high that the enzymes are swept
away from the reactor entirely. This causes low mixing; these type of reactors are highly
suitable for the exothermic reactions. It is most often applied in immobilized enzyme
catalysis
Figure 20. Fluidized bed reactor.
E. Low cost treatments.
Used in small and medium-sized municipalities, these are lagoons, oxidation
ponds and green filters. These methods are secondary treatments as they eliminate
biodegradable organic matter.
Lagoons. These treatments consist of a preliminary treatment, screening, and a
secondary treatment in which organic matter in wastewater is removed.
Can be classified into natural and aerated.
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71. a) Natural:
Organic matter is eliminated by natural regeneration, aerobical or anaerobical.
Mechanical aeration is not used.
Anerobic lagoons. Depth over 2 m. Organic matter is decomposed in absence of O2.
Organic load is higher in this type of lagoon. Sludge formed by the particulate matter
settled is digested at the bottom.
Anaerobic-aerobic lagoons. In this case there are two different treatment areas:
Aaerobic in the upper zone and anaerobic in the lower where sludge digestion is
achieved. Depth varies between 1-2 meters.
Maturation lagoons. For aerobic process takes place depth is limited to 0,3-1 m.
Elimination of pathogenic organisms is achieved by sunlight irradiation
b) Aerated.
Aerated lagoons are used to avoid problems of smells, using mechanical aeration
systems, which makes it possible to adapt the process to load changes and seasonal
conditions and to improve mixing.
Some of the lagoons may be operated as settling ponds and in some cases sludge
return is applied.
These processes are a suitable solution when the cost of land is not very high, the
organic loads can fluctuate and there is no need for qualified personnel. Operating costs
are therefore low.
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72. Figure 21. General view of an aerated lagoon.
• Green filter. It consists in a field where crops or forest are watered regularly with
sewage. The purpose of this process is to purify the wastewater through the joint action
of soil, plants and microorganisms.
The wastewater purification takes place in a biologically active layer whose depth
does not exceed 1.2 m. deep. Water passes through this layer slowly, so that two
processes take place:
• suspended solids are retained in the soil which acts as a filter.
• organic matter is mineralized by a bacterial biochemical oxidation. This is an aerobic
oxidation in which the necessary oxygen is present in the active layer.
Cleansing carried out by some macrophyte plants takes place at the same time,
removing organic matter, nutrients and minerals needed for their metabolism. Examples
of macrophytes used are: poplar, water hyacinth and steeple.
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73. Figure 22. General view of green filter.
• Peat beds. This treatment consists of three layers: peat, sand and gravel. The process is
based on peat adsorbing characteristics, qualities and formation of complex substances
from dissolved and colloidal substances. At the same time, a mechanical retention of
materials in suspension and a biological treatment takes place in the bed.
7.4. Tertiary treatment.
The main objective of tertiary treatment is the elimination of specific pollutants
present in wastewater. For example, removing nitrogen and phosphorus salts may be
required, since an excess of these compounds causes eutrophication problems.
Tertiary treatments are expensive, so that it’s only applied in case of wastewater
reuse, to remove any particularly dangerous pollutant or in case of discharge to a
sensitive area. These treatments are also applied to network or pit water supply for
industrial use.
Tertiary treatments include:
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74. A. Treatments for nutrient removal.
According to the Directive 91/271/EC, on 21 May 1991, nutrient removal is
necessary when the plant discharges its effluent to an area classified as sensitive, that is,
where there may be danger of eutrophication.
Nitrogen removal is biological. It involves an anoxic reactor, operated in the
absence of O2.. In these conditions, a certain type of bacteria reduces NO3 to N2 to
obtain enough energy for metabolism.
Obviously for denitrification to be carried out, aerobic nitrification has been
previously achieved in the reactor, because the nitrogen that enters the treatment is not
as nitrates, but mainly as ammonia.
Phosphorus can be removed either chemically or biologically. Chemical
elimination is achieved by precipitation, in the primary, secondary decanter or in a
tertiary treatment tank by adding FeCl3.
Biological elimination takes place in an anaerobic-aerobic activated sludge
process. Anaerobic bacteria have the capacity of releasing phosphorus under anaerobic
conditions, adsorbing a greater quantity than the absorbed under aerobic conditions,
achieving an accumulation of phosphorus in these microorganisms, carried out of the
system in the excess sludge.
B. Adsorption.
Adsorbent substances have the property of fixing organic molecules extracted
from the liquid phase on its surface. The most important are: silica gel, alumina,
functional resins and activated carbon. Activated carbon is the most used due to its price
and its specific surface. It is used to remove: detergents, dyes, chlorinated solvents,
aromatic derivatives, phenols, flavours and smells.
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75. It is found in two forms: beans and powdered.
• coal beans. Used as filtering bed crossed by water, with four functions: filtering,
support bacterial catalytic action with chlorinated compounds and adsorption (the latter
is the main).
• powdered coal. Used closely mixed with the wastewater and subsequently separated
by flocculation and filtration. So handling and employment are more difficult.
C. Ion exchange.
This process involves the replacement of one or more ions present in the water to treat
for others who are part of a finely divided solid phase.
There are two types of ion interchanges:
• cation exchanger. In this type, acid radicals present in their molecules are exchanged
for minerals or organic cations.
• anion exchangers. Base radicals are exchanged for minerals or organic anions.
The regeneration of the interchanger is done in contact with a dissolution of the
concentrated ion shifted.
The ion-exchange resins are applied to waters with a certain quality, and when we
intend to obtain a high purity water.
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76. D. Membranes.
The processes of separation by membranes remove the dissolved matter in water
to treat. These processes can be classified depending on the driving force of separation.
Thus, we find processes whose separation is effected by the pressure difference between
the two sides of the membrane (microfiltration, ultrafiltration, reverse osmosis and
nanofiltration) and processes in which the driving force is the electrical potential
difference between two electrodes (electrodialysis ). There are other membrane
processes in addition to those already mentioned, but not as important as the ones before
mentioned.
• Ultrafiltration and microfiltration. Ultrafiltration and microfiltration differentiate by
the size of molecules that separate. Molecules of molecular weight of aproximately
1000 Daltons can be separated by ultrafiltration.
Membranes consists of a layer support and an active layer; the layer selectively
carried out by the separation, so that the molecules with a larger size than the pores are
retained. Besides the size there are other factors that influence in the performance of
separation, such as the geometry of molecules, interaction with membranes, etc...
Membranes can be made of both organic (polymer) and inorganic materials. The
latter shows greater resistance.
Examples of ultrafiltration application are; painting booths wash water treatment
by electrophoresis and separation of oils.
Figure 23. View of a MBR reactor.
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77. • Reverse osmosis and nanofiltration. Reverse osmosis consists in applying a pressure to
water higher than its osmotic pressure, so that it flows from through a semi permeable
membrane from the more concentrated stream to to the less concentrated, removing
salts from water, which are retained on the more concentrated stream.
Reverse osmosis and nanofiltration allow to conduct water demineralization.
Nanofiltration membranes perform high rejection index for divalent salts, whereas to
separate monovalent salts, reverse osmosis must be used.
The processes are identical, but nanofiltration usually works at lower pressure,
and it is used when there is no need to reach high rejections of salts. Reverse osmosis
membranes, unlike the microfiltration and ultrafiltration ones, are dense, that is not
present pores, whilst flow through the membrane is due to diffusion. Nanofiltration
membranes exhibit characteristics intermediate between those of reverse osmosis and
ultrafiltration.
The materials of these membranes are usually cellulose acetate and aromatic
polyamide derived. Applications of reverse osmosis are desalination and water recovery
and recovering of some metals.
• electrodialysis. In this process an electric field is applied to a high concentrated in ions
solution, so cations displace to the negative electrode and anions to the positive
electrode.
If the electrodes are placed between a set of selective membranes arranged
alternately, ions migration is limited. Demineralized water is produced using this
process. However, non-ionized molecules and colloids remain in the treated water.
77

78. Feed
Catode Anode
- +
Na+ Na+ Na+
C A C A
Cl- Cl- Cl-
C A C A
C A C A
Na+
C A C A
-
Cl
Memb 1 Memb 2 Memb Memb
4 Concentrate
outflow
Figure 24. Electro dialysis process scheme.
The table below shows a summary of some membrane separation processes, and
compounds that can be separated by each of them.
Table 8. Summary of membrane separation processes.
Membrane process Removed product
Reverse osmosis Monovalent salts
Sugar
Vitamins
Nanofiltration Divalent salts
Sugar
Ultrafiltration Proteins
Polisacarids
Pirogens
Virus
Microfiltration Virus
Bacteria
78

79. E. Advanced oxidation: Some industrial wastewater pollutants are non-biodegradable
and that should be eliminated to avoid an impact on the environment. In recent years
some oxidation processes have been developed envolving certain high-oxidant
compounds that are capable of destroying these molecules, either completely
decompose in CO2 and H2O or transforming them into less dangerous compounds.
Wastewater advanced oxidation is carried out with:
• Ozone (O3)
• Hydrogen peroxide (H2O2)
• Combination of O3 and UV radiation.
• Combination of O3, UV radiation and H2O2.
• O2 at high pressures and temperatures (wet oxidation).
These techniques are applied for example to eliminate phenols, pesticides, etc..
7.5. Other treatments:
• Disinfection. Disinfection is the elimination of pathogenic organisms in water. This
type of treatments is used in drinking water purification plants and WWTP.
• Drinking water plants: In this type of plants all microorganisms that water could
contain are removed to avoid the risk of disease at drinking water.
• WWTP. The purpose of disinfection is to improve water quality obtained after the
secondary treatment with a view to re-use in agriculture. It is worth mentioning that in
Spain it is forbidden to obtain drinking water from wastewater, thus regenerated
wastewater can only be used for irrigation.
Water reuse in agriculture is also subjected to quality requirements to achieve
concentration limit of pathogenic organisms depending on the case of use.
79

80. The disinfection can be carried out by filtration or by inhibition of germs.
A. Filtration of germs.
The processes for filtering germs are ultrafiltration and microfiltration.
B. Inhibition of germs.
It can be achieved by physical or chemical means.
• Physical means. As temperature and ultraviolet radiation.
If high temperatures are applied to a wastewater for some time, elimination of
pathogens will the place, as in pasteurization.
Ultraviolet radiation is produced by a quartz lamp. The mechanism of action is based in
destruction of cell protoplasm of microorganisms caused by a reaction that ultraviolet
radiation initiates, preventing further reproduction or even causing microorganisms
death.
The wavelength most often used is between 250 and 270 nm.
Figure 25. UV lamps for effluent disinfection.
80

81. • Chemical. This is application of ozone or chlorine.
• Ozonation. Ozone disinfectant action is achieved as it breaks down easily in
accordance with the following response:
O2 + O •→ ⎯O3
atomic oxygen being the strongest oxidizer known, which destroys pathogens.
Ozone is produced by high voltage electric shocks, which transforms a part of oxygen in
air into ozone.
Figure 26. Ozonation equipment.
• Chlorination. Chlorine is an oxidant that destroys organic matter, destroying enzymes
essential for pathogens life.
Factors affecting its destruction effectiveness are: the nature of disinfectant, its
concentration, the contact time, temperature, pH, and the types and concentration of
microorganisms.
81

82. 8. Sludge treatment.
Sludge is settled in primary and secondary clarifiers. These are characterized as
being extremely liquid (primary sludge contains approximately 1.5% solids and
secondary barely exceeds 0.5%) as well as highly reactive, thus uncontrolled
decomposition reactions of organic matter take place.
Sludge produced in WWTP requires a certain stabilization to be managed and
evacuated for the fore mentioned characteristics. That is why we have been conducting
in the same treatment of sewage sludge to prepare them for further evacuation.
The two main objectives of sludge treatment are:
• Reducing the volume to treat by removing some of the water.
• Reduction of organic matter to avoid uncontrolled reactions of decomposition
(stabilization).
The following are the processes that are used for treating sludge.
8.1. Concentration.
As mentioned before, since the sludge from wastewater treatment is liquid, we
first need to concentrate. Several methods are applied:
A. Thickening. Sludge is introduced into a settling tank, with a high retention time,
what causes the compression of the sludge in the lower area. These tanks are often
covered to prevent the proliferation of odors.
B. Flotation. It involves injecting pressurized air to the sludge, so that when passing to
the flotation tank air bubbles are released dragging suspended particulates to the
surface. The mantle of sludge formed on the surface is scrapped out by surface blades.
This method is used for light sludge such as secondary sludge.
C. Centrifugation. This method allows us to get at the same time concentrated and
dehydrated sludge. It is considered at the dewatering point.
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83. 8.2. Destruction of organic matter.
To accomplish this goal following processes are used:
A. Aerobic digestion. It consists of an aerobic oxidation of organic matter in a sludge
reactor that differs from the active sludge reactor at the high retention time. The
aeration of the reactor is similar to that of the active sludge reactor.
B. Anaerobic digestion. Estabilization takes place in the absence of O2. The simplest
theory that explains the processes of anaerobic decomposition of organic matter is based
on the existence of two stages, that is to say, two groups of bacteria that act
simultaneusly to breakdown proteins, fats and carbohydrates. According to this theory,
facultative anaerobic bacteria decompose high molecular weight substances into short-
chain fatty acids (acetic, butyric) and alcohols. Finally, anaerobic bacteria convert these
substances in CH4 and CO2.
In fact, this process is more complex and thus has established the theory of the
four stages or phases:
1. Hydrolysis. Substances of high molecular weights are broken down into shorter-chain
molecules.
2. Acidification. Facultative and strict anaerobic bacteria form short-chain fatty acids
(such as acetic and butyric), alcohols, H2 and CO2. Of these substances methanogenic
bacteria can only use acetic, H2 and CO2 for obtaining methane.
3. Acidic. Acids and alcohols are converted to acetic acid.
4. Methanogenic. Methane is generated primarily from acetic acid, though it can also be
generated from. H2 and CO2.
The decomposition of a complex organic substance to methane is a fast process if
methanogenic bacteria have the necessary food available. The transformation of the
"cracked molecules" at the stage of acidification and the formation of methane at the
methanogenic phase from acetate occur in practice without difficulty if the environment
is favorable.
83

84. Figure 27 a. Anaerobic sludge digestion phases.
There are a number of parameters that limit the process performing:
• Temperature. When the temperature rises, the speed of biological reactions is higher,
reaching a maximum temperature. So if we heat sludge, greater efficiency in the
operation and lower residence times are achieved. Mesofilic operation temperature
ranges from 35 to 37 ° C. Above this range, energy expenditure does not compensate for
the increase in the speed of reaction.
• Oxygen. The presence of oxygen, no matter how little it may be, can be deadly to
methanogenic bacteria. Therefore, the digestion tank must be closed.
• pH. The optimum pH for anaerobic digestion is 6,8-7,5.
• Nutrients. A minimal amount of nutrients is required for microorganisms.
• Toxic compounds. There are some compounds that are toxic to methanogenic bacteria;
such as, heavy metal ions and organochlorine compounds.
The anaerobic processes are less stable than the aerobic. This makes necessary to
control the reactor where digestion occurs. Normally complete mix digesters are used,
in which stirring is achieved by mechanical agitators, or sludge recirculation of biogas
produced.
The composition of the digestion gas varies with the characteristics of sludge to
be digested. The content of CH4 is between 60 and 70% of volume and the calorific
capacity ranges between 6 and 7 kW • h/Nm3.
84

85. In addition to CH4 and CO2, gas digestion contains SH2 at concentrations between
0.1 to 10 g/Nm3. Other impurities are generally not significant but can be present in
some n isolated cases.
Biogas can be used for warming the digester and for producing electricity. Biogas
surplus is normally burnt.
Figure 27 b. Anaerobic sludge digestion.
C. Sludge incineration. A double process is carried out by the incineration of sludge:
first, total elimination of water (drying sludge), and secondly, the burning of organic
matter present in the sludge. Depending on the type of sludge adding fuel may be
required.
Among the incineration systems employed we have:
• Multi stage furnace. The sludge flows from the upper to the lower part of the furnace,
against flow with the combustion gases, leading from dehydration to incineration as
they pass from upper to lower plates.
• Spray oven. In this case the sludge is introduced finely divided, thus facilitating to be
dried by hot air. When dry, sludge is taken out at the bottom as powder.
• Revolving oven. It is a cylinder that rotates very slowly on an inclined shaft. Sludge
and circulating air flow at counter flow.
85

86. 8.3. Sludge conditioning.
The sludge from urban wastewater and many of the industrial wastewater plants,
present a colloidal structure that hinders its filtration. Therefore, flocculants are added to
break the colloidal structure and provide them with a granular texture that is easier to
filter.
8.4. Sludge dewatering.
Once reduced the power of fermentation of sludge, its volume is reduced by
removing water content. There are several methods for doing so: natural drying, vacuum
filters, press filter and centrifuge.
A. Natural drying. It consists of an outdoors bed of sand and-gravel with a good
drainage system on which sludge is extended. The water is removed by two processes:
natural evaporation and gravity or induced drainage. The sludge is usually dry when its
moisture is below 65%.
B. Vacuum filters. This type’s most widely used is rotating drum. This consists of a
revolving cylinder which is partially submerged in a tank containing the sludge. In the
production of vacuum, liquid is aspired, as solid matter is retained on a canvas, forming
the "cake" that is thickened. The water is drained in a pipeline inside the cylinder.
Moisture present in dewatered sludge ranges 70-80%.
C. Press filters. There are two types:
• Plate filter press. Consist of a series of plaques with filter cloth attached on both sides.
The plates are upright pressure is applied by means of a hydraulic system. This system
is commonly used to dewater industrial sludge, to reduce the moisture to 50%.
86

87. Figure 28. Plate filter press.
• Belt filters press. The basis is a simple concept. Sludge sandwiched between two
porous belts is passed over and under various diameter rollers. As the roller diameter
decreases, pressure and shear forces are exerted on the sludge. (Figure 12). Dewatered
sludge is usually between 18 and 25% solids depending on its characteristics.
Figure 29. Belt filter press.
87

88. D. Centrifuges. Principle of operation consists of separating solids form liquids by the
use of the centrifugal force. It can be applied for both sludge concentrating and
dewatering. Sludge is pumped into a rotating cylindrical-conical bowl that spins at high
speed, so that sludge (with higher density than water), is separated from water, thrown
to the walls as water stays in the center. A helical screw conveyor causes the solids to be
conveyed and being discharged.
Figure 30. Centrifugal decanter.
8.5. Thermal drying systems.
Based on applying needed heat, to evaporate the water content in sludge. There
are basically two types, direct and indirect. In direct type sludge gets in contact with
steam, while in the indirect type heat transfer is done through a plate of a heat
exchanger. This method allows getting 90-95% solids in sludge, not possible to achieve
through mechanical dewatering. With this method, therefore, a large reduction in the
volume of sludge produced occurs and, the final product can be used as fuel of low
quality or applied to agriculture.
88

89. Figure 31. Thermal drying system.
8.6. Final disposal.
Can be classified into:
• Composting. A sludge supplies nutrients and porosity to the soil.
• Sale of products. For example, ashes produced in incineration can be sold as material
used to build roads.
•Discharge to a landfill.
The reuse of sludge in agriculture as fertilizer is regulated by the RD 1310/1990
of October 29, which establishes limits on the content of heavy metals in sludge and
soil.
At this time there is no legislation in the requirements regarding the amount of
pathogens in sludge, though there is a Europe Directive draft supposed to be approved
in short term.
89

90. 9. Examples of urban wastewater treatment.
In figures 29 and 30 schemes of the water and sludge lines of WWTP urban and
middle-sized or large (50.000 inhabitants equivalent).
Figure 30. Water line of a conventional activated sludge WWTP.
2 3
4
0 7
1 6
8
2 3
4
7
6
8
9
0. Raw wastewater 5. Chlorination
1. Preliminary treatment 6. Primary sludge 5
2. Primary clarifiers 7. Sludge return
3. Active sludge reactor 8. Sludge surplus
4. Secondary clarifiers 9. Effluent
Figure 32. Water line of a conventional activated sludge WWTP.
The wastewater is conveyed by sewers to the WWTP. Once there is preliminary
treated in order to remove fats, oils, and greases (also referred to as FOG), sand, gravels
and rocks (also referred to as grit), larger settleable solids and floating materials (such
as rags and flushed feminine hygiene products).
This primary treatment consists in a screening stage through large and small
spacing screens, and a sand or grit channel where sand and grease are removed, which
must to be managed.
90

91. In the primary settling tanks solids are removed from water by gravity, removing
approximately 30% of the initial BOD5 in wastewater. At this stage primary sludge is
generated, which will be treated at the same plant.
The secondary treatment consists of a activated sludge reactor where the main
elimination of organic matter takes place and a secondary settling tank in which active
sludge is removed from treated wastewater. Active sludge consists of micro organisms
forming floccs which settle in the secondary clarifier. Most of micro organisms are
returned to the reactor, to keep the process and the surplus is purged out the waster line
to the sludge line to be treated.
At the end of the water line a tertiary treatment may be implemented to reach
quality standards for reusing, i.e., in irrigation, industry recreational, etc.
1 5
3
2
4
5
1. Primary sludge 7
2. Biological sludge surplus 6
3. Gravity thickener
4. Flotation
5. Anaerobic digestion
6. Sludge dewatering
7. Sludge disposal
Figure 33.Scheme of the sludge line of a conventional activated sludge treatment plant.
91

92. In the sludge line there is a first stage of thickening to reduce the sludge volume to
manage, by means of gravity thickening or flotation. The clarified part of both processes
is returned to the begining of the water line.
The thickened sludge is mixed and pumped to the digestion stage. Anaerobic
digestion is the stabilization system used in the medium and large size WWTP. It
operates in mesophile rank and sludge hydraulic retention time in the reactor is between
10 and 15 days. At this stage 50% of organic matter is eliminated. Once digested,
sludge is mechanically dewatered, generally using belt filters presses or centrifuges,
obtaining 20-25% solid in sludge to be disposed, as water removed is returned to plant
header.
92