Waste water treatment technology SH/pdf

Sardar Hussain
Asst prof.Biotechnology
Government science college,
chitradurga

Content
1. Background
2. Typical composition of domestic waste water
3. Strategies of waste water
4. Overview of waste water
5. Preliminary waste water treatment
6. Primary waste water treatment
7. Secondary waste water treatment
8. Tertiary waste water treatment
9. Summary
10.Refrences
2SH/BIOTECHT/LECTURE/GSC/CTA

Background
➢ Waste water or sewage is the liquid waste arising mainly from
domestic or industrial sources
➢ a) Domestic Waste Water Characteristics:
➢ The characteristics of waste water are physical, chemical and
microbiological components (total solids, temperature, pH, colour,
odour, carbohydrates, proteins, fats, BOD, heavy metals, sulphur,
bacteria, algae, virus etc.). In domestic waste water specific toxic
and hazardous compounds may exist, i.e. phenols and toxic
organics.
➢ (b) Industrial Waste Water Characteristics:
➢ Each industry is individual. It is not possible to enumerate wastes
from all industry types as many wastes are specific lo particular
industries, Industrial waste water vary considerably in their nature
and toxicity.

Typical composition of domestic waste water

➢ When effluent (waste)discharged into a river body
such as lake, river or sea a number of process occur
like physical, chemical and biological characteristics
of water change which cause loss of organism.
➢ The extent of damage depend upon type of
pollutant present in effluent. Non bio-degradable
pollutant like mercury are most deadly as they
accumulate in aquatic organism which lead to
Biomagnifications.
➢ Large quantity of biodegradable waste can affect
living organism in the water bodies in which waste
are discharged.
➢ It is necessary to treat effluent or waste water
before discharging in water body. The treatment
procedure are generally divided into three groups-

1
• Preliminary treatment
2
• Primary Treatment or Mechanical Treatment
3
• Secondary Treatment or Biological Treatment
4
• Tertiary treatment

• Preliminary treatment involves the removal of
floating materials (leaves, papers, rags) and
settle able inorganic solids (sand, grit), besides
oily substances (fats, oils, greases). The three
major types of equipment-screeners, grit
chambers, and skimming tanks, employed in
preliminary screening are briefly described.

• Physical Treatment-removal of the coarse fraction.
• Oil, fatty acids and suspended solids could be
removed by the use of the following techniques:
• Screeners-(to remove floating materials and suspended
particles)
• Grit Chamber-(heavy inorganic materials like sand ash
can removed it works on sedimentation due to
gravitational forces)
• Floatation or skimming tank-greasy and oily materials
can be removed
• Compressed air is pushed from floor of the tank raising
bubbles coagulate and solidify oily and greasy material

• A screener is a device with openings (usually uniform in
size) to remove the floating materials and suspended
particles. The process of screening can be carried out by
passing sewage through different types of screeners (with
different pore sizes).
• The screeners are classified as coarse, medium or fine,
depending on the size of the openings. The coarse screen
has larger openings (75-150 mm). The openings for
medium and fine screens respectively are 20-50 mm and
less than 20 mm. Different types of screens-fixed bar
screen (coarse or medium) disc type fine screen, drum
type fine screen are in use.
• A shredder or comminatory is a special screen that can
cut and retain the floating and suspended materials

(A)Screener (B)shredder

Grit tank
• The heavy inorganic
materials (specific gravity
2.4-2.7) like sand, ash and
others can be removed by
using grit chambers. This
technique is based on the
process of sedimentation
due to gravitational
forces. Grit chambers may
be kept either before or
after the screens.

Skimming Tanks:
• Several greasy and oily materials (fats, oils, waxes,
soaps etc.) from the domestic or industrial outlets find
their entry into the sewage. They can be removed by
using a skimming tank which is fitted with baffle walls
that divide the tank The skimming tank is divided into
three compartments that are interconnected.
• As the compressed air is pushed from the floor of the
tank, the raising air bubbles coagulate and solidify the
oily and greasy materials present in the sewage. This
material is pushed to the side compartment referred to
as stilling compartment from where it can be removed
manually or mechanically.

• Primary treatment is aimed at the removal of fine
suspended organic solids that cannot be removed in the
preliminary treatment.
• Primary treatment basically involves the process of
sedimentation or settling. In the normal process of sewage
treatment, sedimentation is usually carried out twice-once
before the secondary treatment, referred to as primary
sedimentation, and then after the secondary treatment is
complete, a process known as secondary sedimentation. It
is sometimes necessary to use chemical coagulants to
facilitate or aid sedimentation, and this process is referred
to as chemical precipitation or coagulation-aided
sedimentation.

• Principle of Sedimentation:
• The solid particle of the sewage tend to settle down due to gravity.. If the
flow of the sewage is stopped and if it is stored in a tank referred to as
sedimentation tank, the solid particles can settle down at the bottom.
The process of sedimentation is influenced by several factors. These
include the size, shape and specific gravity of particles, besides viscosity
and flow velocity of sewage.
• Types of Settling:
• discrete settling (particles which do not change their size, shape and
weight are referred to as discrete particles or granular particles)
• flocculent settling(The flocculent particles can change their size, shape
and weight, and thus lose their identity. These particles actually coalesce
during settling. Settling of bioflocs, and chemical )
• hindered or zone settling (particles as such, tend to remain in a fixed
position with respect to each other. When flocculated, the whole mass of
particles settle as a unit or a zone)
• compression. (Settlement of particles in the lower layers can occur by
compression of the weight of the particles on the upper layers)
• This categorization is mainly based on the tendency of the particles to
interact and form solids.

Chemical-aided Sedimentation:
➢ Addition of certain chemicals aids sedimentation, a process referred to as
chemical-aided sedimentation.
➢ By this technique, about 60-80% of the suspended particles can be removed.
➢ Chemical precipitation involves three stages—coagulation, flocculation and
sedimentation.
➢ Coagulation is mainly a chemical process wherein the charged particles are
destabilized (by the addition of chemical agents).
➢ Flocculation involves the physical phenomena of aggregating the destabilized
particles to finally form settle able solids (i.e. sedimentation). The chemicals used
in chemical-aided sedimentation are of two types-coagulants and coagulant aids.
➢ Coagulants: These are the chemicals (normally positively charged) which form
insoluble and gelatinous precipitates with colloidal particles (negatively charged
ones present in sewage). The most commonly used coagulants in sewage
treatment are alum (alluminium sulfate) iron salts (ferric sulfate, ferrous sulfate,
ferric chloride), lime and soda ash (sodium carbonate), sodium silicate and sodium
aluminate.
➢ Coagulant-aids-activated silica, weighting agents (e.g. powdered lime stone or
silica) and polyelectrolytes.

• Biological treatment of sewage is required for the removal
of dissolved and fine colloidal organic matter.
• This process involves the use of microorganisms (bacteria,
algae, fungi, protozoa, rotifers, nematodes) that
decompose the unstable organic matter to stable inorganic
forms.
• The biological treatment processes of sewage are broadly
classified as
• aerobic,
• anaerobic
• pond processes.

Activated Sludge Process:
• The activated sludge process, first developed in England in 1914,
continues to be the most commonly used modern process for the
biological treatment of sewage.
• In this method, the sewage containing organic matter with the
microorganisms is aerated (by a mechanical aerator) in an aeration tank.
• Under aerobic conditions, the microorganisms metabolize the soluble and
suspended organic matter. The generalized metabolic reaction is as
follows.
• A part of the organic matter is utilized for the synthesis of new bacterial
cells while the remaining gets oxidized to CO2 and H2O. The newly formed
microorganisms are agglomerated to form floes, technically referred to as
sludge.
• The separated sludge which is not in contact with organic matter becomes
activated. It is separated from the settling tank, and returned to the
aeration tank, and recycled. The activated sludge recycled in aeration tank
serves as a seed or inoculum. The excess and waste sludge can be
removed.

Factors affecting performance:
• There are several factors that influence the efficiency of activated sludge process,
the most important being the type of the reactor, aeration, food microorganism
(F/M) ratio, nutrients, sludge recirculation rate, besides pH and temperature.
• Advantages:
• The activated sludge process is a very compact, low-cost and an efficient biological
treatment system for sewage treatment.
• It is worked out that under ideal conditions, up to 95% of BODs, 98% of bacteria
(particularly coliform) and 95% of suspended solids can removed by activated
sludge process. The excess and waste sludge has a higher fertilizer value compared
to other treatment processes.
• Disadvantages:
• There is production of large volumes of sludge which sometimes becomes difficult
to handle. Power consumption is relatively high for operation.
• Supervision by skilled personnel is necessary.
• Conventional activated sludge process:
• The conventional activated sludge system consists of a separation tank, settling or
sedimentation tank and sludge removal line The sewage after the primary
treatment is introduced at the head of the tank. It is desirable to supply
O2 uniformly throughout the tank.

Aerated Lagoons
• Aerated lagoons, also called as
aerated ponds, wherein surface
aerators are installed to
overcome the bad odours (due to
overload of organic materials).
• The microbiological treatment of
aerated ponds is comparable to
the activated sludge process.
• The major difference is the large
surface area in aerated ponds and
this is more susceptible for
temperature effects. It is possible
to carry out continuous
nitrification in aerated lagoons.

Sequencing Batch Reactor:
The major difference between the
conventional activated sludge
system, and SBR is the two
processes aeration and
sedimentation are carried out
sequentially in the same tank in
SBR in ASP both are carried in
separate tanks.
The process is carried out in a
sequence of five steps —
filling,
aeration (reacting)
sedimentation (settling),
decanting
Idle

Aerobic Digestion:
• The organic sludge’s produced from various treatment processes (activated sludge
treatment, trickling filter-sludge) are subjected to aerobic digestion in special
reactors referred to as aerobic digesters.
• Aerobic Attached — Growth Treatment Processes:
• Aerobic attached-growth treatment processes are commonly used to remove the
organic matter found in the sewage. These processes are also useful for the
nitrification (conversion of ammonia to nitrate).
• The commonly used attached-growth processes are listed:
• i. Trickling filters
• ii. Roughing filters
• iii. Rotating biological contractors
• iv. Packed bed reactors.
• Among these, trickling filter is most widely used.
• Trickling Filters:
• Trickling filters, also known as percolating or sprinkling filters, are commonly used
for the biological treatment of domestic sewage and industrial waste water. In a
strict sense, trickling filters are not filters, but they are oxidation units.
• It has a bed of course, hard and porous material over which sewage is sprayed. In
about two weeks time, the biomass attached to the media surface grows and
forms a layer, referred to as biological film or microbial slime.

• This film has a thickness of 0.1 to 2.0 mm and is rich in microorganisms.
• As the liquid (sewage) trickles through the biofilm, the organic matter gets oxidized to CO2 and
NO2 by the microbial metabolism.
• This oxidation is carried out by the aerobic organisms (particularly bacteria) that are present on
the upper portion of the biological film.
• The biological film is rich in the bacteria- Pseudomonas, Flavobacterium, Alcaligenes, and algae-
Chlorella, Utothrix, and Stigeoclonium, besides some fungi and yeasts.
• Biofilms with a thickness in the range of 70-100µm are efficient for the treatment process.
• As the biofilm ages, its thickness increases and it automatically settles to the bottom of the tank.
The waste waters obtained in milk processing, paper mills and pharmaceutical industries are
treated by trickling filters.
• Factors affecting performance of trickling filters:
• The type of the media and its depth, organic and hydraulic loading, filter staging, recirculation
rate and flow distribution are the important factors that influence the performance of the
trickling filters.
• Advantages:
• Trickling filters are simple, occupy less space and the operating costs are low. They operate
efficiently in hot climate and thus are suitable for most developing countries (like India).
• Disadvantages:
• Removal of BOD is moderate (around 70%), and disposal of excess sludge is necessary. Primary
sedimentation is required, since trickling filters cannot handle raw sewage.

Packed-Bed Reactors:
• Packed-bed reactors or
fluidized bed reactors are
used for the removal of
BOD and nitrification. A
reactor is packed with a
medium to which the
microorganisms get
attached and form biofilms.
The sewage along with air
(or pure oxygen) is
introduced from the bottom
of the reactor . The main
advantage with packed bed
reactors is that they have
high surface area of biofilms
for unit of reactor.

Anaerobic Digestion:
• Anaerobic digestion is mostly
useful for the stabilization of
concentrated sludge’s that are
produced on the treatment of
industrial sewage. A
diagrammatic representation of a
typical high-rate, complete mix,
and single stage digester is
depicted in Fig.
• The process of anaerobic
digestion is carried out in an air
tight reactor. Sludge is introduced
continuously or intermittently. In
the high-rate digestion system,
the contents of the digester are
heated and mixed completely.
And it takes about 15 days for the
process to be complete.

Biodegradation of organic matter of sludge (sewage)
• The biological degradation of organic matter of sludge occurs in three
stage(hydrolysis, acidogenesis and methanogenesis.

➢ Hydrolysis:In the enzyme-catalysed reactions, high molecular weight compounds (proteins,
polysaccharides, lipids and nucleic acids) are degraded to low molecular weight compounds
(amino acids, monosaccharide’s, fatty acids, purines and pyrimidine’s).
➢ The latter serve as substrates for energy supply and microbial growth.
➢ Acidogenesis:
➢ The low molecular weight compounds are converted to acidic products (propionate, butyrate,
and lactate).
➢ Methanogenesis:
➢ This is the third and final stage and involves the production of methane and carbon dioxide,
from the intermediates formed in acidogenesis. Methane gas is highly insoluble and its
departure from the digester represents the stabilization of sewage or sludge.
➢ Microorganisms to degrade organic matter of sludge (or sewage):
➢ A consortium of anaerobic microorganisms work together for degradation of sludge (or sewage)
organic matter.
➢ 1. Acid-forming bacteria:
➢ These are also known as acidogens or non-methanogenic bacteria. They bring out the
hydrolysis of macromolecules (e.g. carbohydrate) to simple substrates (e.g. monosaccharide’s),
and the latter to acids e.g. Clostridium sp, Corynebacterium sp, Lactobacillus sp, Actinomyces
sp, Staphylococcus sp, Peptococcus anaerobus, Escherichia coli.
➢ 2. Methanogenic bacteria:
➢ These bacteria, also referred to as methanogens or methane formers are responsible for the
conversion of acetic acid and hydrogen to methane and carbon dioxide. The most important
methanogens belong to the genera Methanobacterium, Methanobacillus, Methanococcus and
Methanosarcina.

Aerobic Ponds
➢ These ponds usually have a depth of about 0.5 to
1.5 feet (150 to 450 mm) and allow the
penetration of light throughout the liquid depth.
➢ In all these ponds, oxygen is maintained through
continuous atmospheric diffusion (by surface
aerators or pumps), besides the production by
algae grown in the pond.
➢ The aerobic stabilization ponds contain bacteria
and algae in suspension. They are particularly
useful for the treatment of soluble wastes.
➢ The algae can carry out photosynthesis and
release oxygen to maintain aerobic conditions in
the pond.
➢ The bacteria degrade the organic matter to
produce CO2 and other nutrients to be utilized by
algae .
➢ Some higher organisms like protozoa and rotifers
present in the pond are responsible for the
polishing of the effluent.

Anaerobic Ponds
• Anaerobic ponds are useful for the treatment of high-strength organic matter and
solid containing sewage/waste water. These ponds are completely devoid of
dissolved O2. They are very deep (up to 30 feet i.e. about 9 m), so that heat
conservation is possible, besides requiring minimum land area (for pond
construction).
• When the sewage is added to the pond, precipitation and anaerobic conversion of
organic waste to CO2, methane and other gases, organic acids etc. occurs. Under
suitable conditions, 75% of the BOD can be removed in anaerobic ponds. The
clarified effluent is usually discharged for further treatment.
• Facultative Ponds:
• In facultative ponds, the treatment of sewage is carried out by a combination of
both aerobic and anaerobic processes. Three types of microorganisms aerobic,
anaerobic and facultative (both aerobic and anaerobic) are employed in facultative
ponds.
• The term oxidation pond or stabilization pond is frequently used for facultative
ponds.
• A diagrammatic view of a facultative pond is depicted in Fig.
• It consists of three zones.

Facultative pond
The sewage organic matter is
stabilized by both aerobic and
anaerobic processes. The algae
present in the aerobic zone carry out
photosynthesis and release O2. This
oxygen is utilized by the aerobic and
facultative bacteria to oxidize soluble
and colloidal organic matter.
Advantages:
For the facultative ponds, the initial
and operating costs are low. There is
no need for skilled personnel.
Disadvantages:
Unpleasant odours and mosquito
breeding are frequently seen in
facultative ponds. The requirement
of land area for construction of these
ponds is more.

4. Tertiary Treatment
• The main function of tertiary treatment is to decrease the load of nitrogen and
phosphorous compound present in the effluent by the following process.
• Precipitation
• Nitrogen Stripping
• Chlorination
• Precipitation:The effluent received after the secondary treatment is mixed with
calcium oxide. The lime then react with phosphorous compound in waste to from
insoluble calcium phosphate, which then settle down a the bottom of settling
tank.
• Nitrogen Stripping: Nitrogen present in waste water is generally in the form of
ammonia gas , nitrates and nitrites. Ammonia is highly undesirable in streams and
lakes because it is extremely lethal to aquatic biota. Nitrogen eventually enhance
Eutrophication in order to remove nitrogen air is forced through the effluent
which thereby result in the removal of ammonia gas.
• Chlorination: It is the process in which chlorine is used to kill micro-organism
• To assist in the formation of floc in the process of coagulation together with other
chemical.
• To prevent corrosion of sewers and to prevent spread of epidemic.

Disinfection
➢ Ultraviolet Light
The water is passed through banks of cylindrical, quartz-jacketed
fluorescent bulbs. Some dissolved materials, such as iron and some
organic compounds, can also absorb some of the light. Ultraviolet
disinfection is becoming more popular because of the increasing
complications associated with the use of chlorine.
➢ Ozone:
Ozone is too unstable to store, and has to be made as it is used. It is
produced by passing an electrical discharge through air, which is
then bubbled through the water. While chlorine can be dosed at a
high enough concentration so that some of it remains in the water
for a considerable time, ozone is consumed very rapidly and leaves
no residual. It may also produce some chemical by-products, but
probably not as harmful as those produced by chlorine.

summary

Refrences
• U.Satyanarayana,Biotechnology,Books and allied (P) Ltd.
• A.H.Patel ,Industrial Microbiology
• Cruger.W and A.Cruger,Biotechnology
• B.D.Singh ,Biotechnology, Kalyani publishers, India.
• www.nptel.com
• www.wikipidia.com
• www.neeri.com

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