Treatment and Recycling of Sewage and Sludge.pptx

Environmental
Technology- Lecture 2
Associate Professor
Institute of Marine Sciences.
University of Chittagong. Chittagong.

Treatment and Recycling of Sewage and Sludge

Sorting and treating waste allows it to be further processed into reusable
materials, thereby maximizing the savings of primary resources and energy
as well as reducing environmental burdens. This process is referred to as
recycling, a key component in modern waste reduction hierarchy „Reduce,
Reuse, Recycle“.
wastewater treatment, also called sewage treatment, the removal of
impurities from wastewater, or sewage, before it reaches aquifers or
natural bodies of water such as rivers, lakes, estuaries, and oceans. In
broad terms, water is said to be polluted when it contains enough
impurities to make it unfit for a particular use, such as drinking, swimming,
or fishing. Water pollution, therefore, is caused primarily by the drainage
of contaminated wastewater into surface water or groundwater, and
wastewater treatment is a major element of water pollution control.

Waste sorting is the core procedure that follows after the separately
collected packaging waste from municipal, commercial and industrial waste
collection has reached our recycling facilities. The aim is to minimize the
amount of waste from businesses, local authorities and households that
ends up in landfill and transform it into valuable resources.
Waste splitting stands at the beginning of the efficient waste treatment
process. The unsorted communal waste is separated into different
fractions and then moved for further treatment and waste recovery. Using
a selective treatment process, fractions high in calorific value are separated
off from commercial and industrial waste, creating a marketable product.
Sorted material is then shredded, pressed into tight bales ready to be
delivered for reuse or further treatment.

Balling presses are used to compress the material and minimize the
volume, thus optimizing storage and transportation efficiency. In addition,
pressed bales can be wrapped to protect the material from environmental
influences, like sun and water and to prevent odor emissions and leachate.
Sewage is the wastewater generated by a community, namely: a)
domestic wastewater, from bathrooms, toilets, kitchens, etc., b) raw or
treated industrial wastewater discharged in the sewerage system, and
sometimes c) rain-water and urban runoff. Domestic wastewater is the
main component of sewage, and it is often taken as a synonym. The
main pollutants in sewage are suspended solid, soluble organic
compounds, and fecal pathogenic microorganisms. A variety of chemicals
like heavy metals, trace elements, detergents, solvents, pesticides, and
other unusual compounds like pharmaceuticals, antibiotics, and
hormones can also be detected in sewage.

Sewage
Water (99.9%) Solids(0.01%)
Organic (70)
Proteins (65) Carbohydrate(25) Fats(10)
Inorganic(30)
Grit Metals

hazardous-waste management, the collection, treatment, and disposal of
waste material that, when improperly handled, can cause substantial harm
to human health and safety or to the environment. Hazardous wastes can
take the form of solids, liquids, sludges, or contained gases, and they are
generated primarily by chemical production, manufacturing, and other
industrial activities.
They may cause damage during inadequate storage, transportation,
treatment, or disposal operations. Improper hazardous-waste storage or
disposal frequently contaminates surface water and groundwater supplies
as harmful water pollution and can also be a source of dangerous land
pollution.

Hazardous waste can be treated by chemical, thermal, biological, and physical
methods. Chemical methods include ion exchange, precipitation, oxidation and
reduction, and neutralization.
The chemical, thermal, and biological treatment methods outlined above change
the molecular form of the waste material. Physical treatment, on the other hand,
concentrates, solidifies, or reduces the volume of the waste. Physical processes
include evaporation, sedimentation, flotation, and filtration. Yet another process is
solidification, which is achieved by encapsulating the waste in concrete, asphalt, or
plastic. Encapsulation produces a solid mass of material that is resistant to leaching.
Waste can also be mixed with lime, fly ash, and water to form a solid, cementlike
product.

Our modern lifestyle provides us the luxury of using various products to make our lives
more comfortable and easy, but it comes at a price. A common byproduct of our
current lifestyle includes wastewater, which can either be in the form of water running
down the shower or runoff from wet roads. This wastewater is unfit for human
consumption or use.
Fortunately, we can make the wastewater potable and usable by employing wastewater
treatment technologies that filter and treat the wastewater by removing contaminants
such as sewage and chemicals.

Physical Treatment of Sewage or Primary Treatment

It is the process of removal of small and large, floating and suspended solids
from sewage through two processes of filtration and sedimentation or like
screening, sedimentation and skimming are used to remove the solids. First
floating and suspended matter is removed through sequential filtration with
progressively smaller pore filters. The filtrate is then kept in large open settling
tanks where grit (sand, silt, small pebbles) settles down. No chemicals are
involved in this process. One of the main techniques of physical wastewater
treatment includes sedimentation, which is a process of suspending the
insoluble/heavy particles from the wastewater
Aluminium or iron sulphate is added in certain places for flocculation and
settling down of solids. The sediment is called primary sludge while the
supernatant is called effluent. Once the insoluble material settles down at the
bottom, It can separate the pure water. The primary sludge traps a lot of
microbes and debris. It is subjected to composting, land fill or anaerobic
digestion to produce biogas and manure.

 Screening is the first step at any wastewater treatment system. This
process essentially involves the removal of large non-biodegradable and
floating solids that frequently enter a wastewater works, such as rags,
papers, plastics, tins, containers and wood. Efficient removal of these
constituents will protect the downstream plant and equipment from any
possible damage and pipe blockages. Wastewater screening is generally
classified into either coarse screening or fine screening.
 Grit Chamber is sedimentation basin placed at the front of wastewater
treatment plant to remove sand, egg shells, coffee grounds and other
non putrescible materials that may clog channels or cause abrasive wear
of pumps and other devices.

 In some larger plants, fat and grease are removed by passing the sewage through a
small tank where skimmers collect the fat floating on the surface. Air blowers in the
base of the tank may also be used to help recover the fat as a froth. Many plants,
however, use primary clarifiers with mechanical surface skimmers for fat and grease
removal.
 The flotation process is also widely used in industrial waste water treatment
plants, where it removes fats, oil, grease and suspended solids from waste
water. These units are called dissolved air flotation (DAF) units. In particular,
dissolved air flotation units are used in removing oil from the wastewater
effluents of oil refineries, petrochemical and chemical plants, natural gas
processing plants and similar industrial facilities.

 Flow equalization is not a treatment process but a technique that improves
the effectiveness of secondary and advanced wastewater treatment
processes. Flow equalization levels out operation parameters such as flow,
pollutant levels, and temperature over a time frame (normally 24 hr),
minimizing the downstream effects of these parameters.
 Wastewater Clarifier or Sedimentation Tank plays an important role either
after or before biological treatment processes to remove heavier sludge
solids by means of settling and separation from the liquid phase. When it is
used ahead of biological treatment, the main advantage is that it could help
towards significant reduction in BOD level and thus, reducing the load feed
into the aeration pond. These types of primary sedimentation tanks were
designed to deal with higher rate of loading and also having shorter
retention time for the water.

Biological Treatment of Sewage or Secondary Treatment

• Biological treatment usually is divided into aerobic
and anaerobic processes.
• “Aerobic” refers to a process in which oxygen is
present, while “Anaerobic” describes a biological
process in which oxygen is absent.

Aerobic Digestion
• Aerobic wastewater treatment processes include simple septic or
aerobic tanks, and oxidation ditches; surface and spray aeration;
activated sludge; oxidation ditches, trickling filters; pond and
lagoon-based treatments; and aerobic digestion.
• Constructed wetlands and various types of filtration are also
considered biological treatment processes. Diffused aeration
systems may be used to maximize oxygen transfer and minimize
odors as the wastewater is treated.

Aerobic Biological Treatment
• Microbes, mainly aerobic heterotrophic bacteria, are involved Designed
to remove (soluble) biodegradable organic matter
• Removal of nutrients. TSS, pathogens and heavy metals is coincidental
usually clarified sewage (primary effluents) is treated
Activated-Sludge Process

Aerobic Biological Treatment
• Primary treatment is omitted in case of small flows and low TSS sewage, and
in hot climates (to avoid/control odor problems)
• SBR, oxidation ditches, aerated lagoons, contact-stabilization process, etc. may
not require primary treatment .
• Treatment involves conversion of soluble organic matter into biological flocs
and their removal as secondary sludge Includes an aeration tank arid a
secondary sedimentation tank .
• Aeration and mixing, and sludge recycling are additional features.
Activated-Sludge Process

Conventional Activated Sludge
• It contains a tank for wastewater aeration followed by a settler and a solids
recycle line.
• The wastewater flows through under constant aeration in the presence of
activated sludge and exits at the end of the tank after 4-8 hours of residence
time.
• The oxygen concentration in the reactor should be 0.5-2 mg/1 throughout,
where values over 2 mg/1 are considered lost energy.

Extended Aeration
• This is the modified form of a conventional activated sludge process in which the
production of excess sludge is minimized by oxidation and an increase in
residence time, i.e. through the larger size of the aeration tank.
• The retention time is extended to 1-2 days, which results in a very low net yield
of sludge due to its consumption of endogenous respiration.
• The main advantage of the extended aeration system is in having the minimum of
sludge handling facilities as compared with other conventional activated sludge
processes.
• The sludge in extended aeration effluents is very light, of non-degradable nature,
and settles with difficulty.
• Therefore, settling tanks are provided with a longer retention time of
approximately 4 hours versus 2 hours for the conventional treatment process

Sequential Batch Reactor
• The unit processes involved in the SBR and conventional activated-sludge systems are
identical.
• Aeration and sedimentation/clarification are carried out in both systems.
• However, there is one important difference.
• In conventional plants, the processes are carried out simultaneously in separate tanks,
whereas in SBR operation the processes are carried out l sequentially in the same tank.
• A unique feature of the SBR system is that there is no need for a return activated-sludge
(RAS) system.
• Because both aeration and settling occur in the same chamber, no sludge is lost in the
react step, and none has to be returned from the clarifier to maintain the sludge content
in the aeration chamber.

Trickling Filter “Biological Air Filters”
• The trickling filter consists of a bed of a highly permeable medium to which
microorganisms are attached and through which wastewater is percolated or trickled.
• The filter media usually consist of either rock (slag is also used) or a variety of plastic
packing materials.
• Rock filter beds are usually circular and the liquid wastewater is distributed over the top
of the bed by a rotary distributor. and the wastewater was allowed to contact the media
for a short time.
• The collected liquid is passed to a settling tank where the solids are separated from the
treated wastewater.
• In practice, portion of the liquid collected in the under-drain system or the settled
effluent is recycled, usually to dilute the strength of the incoming wastewater and to
maintain the biological slime layer in a moist condition.
• The limitations of the trickling filter included a relatively high incidence of clogging, the
long rest period required, and the relatively low loading that could be used

Anaerobic Digestion
The anaerobic digestion optimally occurs between 30 to 38 degree Celsius and can be done in
single stage digestion system or two-stage digestion system. In the prior, all the reaction stages
occur in the same anaerobic digestor. So care must be taken so as not to overfeed or underfeed the
digestor with new sludge. Overfeeding may quickly produce acids in digestor and it can inhibit the
slower gasification stage.
Anaerobic lagoons, for example, have all reactions of anaerobic digestion in one area. These are
economical but the rate of digestion can be very less. In the latter case, hydrolysis and acid
generation happens in one digester and the resultant is transferred to another digestor wherein
gasification takes place. This allows for more control on the digestion process.
Irrespective of single or two stage digestion system, in general, the frequency of pumping the
sludge to the digestor needs to be standardized so that uniformity of digestion rate can be
maintained. Further, mixing (using, for example, mechanical or gas mixers or recirculation pumps)
is necessary to prevent stratification of sludge in the digestor which can affect performance.

Chemical Treatment of Sewage or Tertiary Treatment

Chemical Characteristics of Wastewater
: This is a method of expressing the acid condition of the wastewater. pH is
expressed on a scale of 1 to 14. For proper treatment, wastewater pH should
normally be in the range of 6.5 to 9.0. The determination of pH value of sewage
is important, because of the fact that efficiency of certain treatment methods
depends upon the availability of a suitable pH value.
: These are gases that are dissolved in wastewater. The specific gases
and normal concentrations are based upon the composition of the wastewater.
Typical domestic wastewater contains oxygen in relatively low concentrations,
carbon dioxide, and hydrogen sulfide.
: The main inorganic materials of concern in wastewater
are chloride, nitrogen, phosphorus, sulfur, toxic inorganic compounds, and heavy
metals.

: Organic matter consists of Carbohydrates such as
cellulose, cotton, fiber, starch, sugar, etc. Fats and oils received from kitchens,
laundries, garages, shops, etc. Nitrogenous compounds like proteins and their
decomposed products.
: There are three ways of expressing oxygen demand as
like as Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD),
Theoretical Oxygen Demand (ThOD).
Chemical Characteristics of Wastewater

Sludge
Sewage sludge is a byproduct of treated wastewater. It is composed of both
organic and inorganic materials, a large concentration of plant nutrients,
organic chemicals, as well as pathogens. Therefore, it is extremely important
to properly treat such sludge in order to minimize its environmental
repercussions.

Sewage Treatment (Chemical)
Chemical Treatment of Waste water is normally preferred when the
wastewater discharge is very small like that produced by industries, which
contain Chemicals.
Chemical Treatment takes place in units which are called reactors,
Chemical treatment of the industrial wastewaters can be achieved from
one of the following methods:
• Neutralization
• Flocculants & Coagulation
• Oxidation
• Ion Exchange
• Ozonation
• Disinfection

Neutralization
The purpose of neutralization is to adjust the pH value to meet the requirements of the different
processing units in the wastewater treatment system. Neutralization may be used in order to treat acid
wastewaters containing metals, the method comprising increasing the pH of the acid waste by addition
of an alkaline reagent, to form a precipitate and collecting the precipitate. This way the incoming
solution is pH adjusted to the optimum range for precipitating metals as hydroxides.
This step is conducted before the main step of wastewater treatment, that is clarification
(=decantation), to fulfill the overall wastewater treatment objectives

Flocculants & Coagulants
Flocculation and coagulation treatment chemicals are used in effluent water
treatment processes for solids removal, water clarification, lime softening,
sludge thickening, and solids dewatering.
Coagulants neutralize the negative electrical charge on particles, which
destabilizes the forces keeping colloids apart. Water treatment coagulants are
comprised of positively charged molecules that, when added to the water and
mixed, accomplish this charge neutralization. Inorganic coagulants, organic
coagulants or a combination of both are typically used to treat water for
suspended solids removal.
Flocculants gather the destabilized particles together and cause them to
agglomerate and drop out of solution. Examples of ChemTreat flocculants
include low, medium, and high molecular weight polymers.

Flocculants & Coagulants
Flocculants gather the destabilized
particles together and cause them to
agglomerate and drop out of solution.
Examples of Chem Treat flocculants
include low, medium, and high
molecular weight polymers.

Oxidation
Oxidation reduces the biochemical oxygen demand of wastewater, and may
reduce the toxicity of some impurities. Secondary treatment converts some
impurities to carbon dioxide, water, and biosolids. Chemical oxidation is widely
used for disinfection.
Ozonation
Ozone (O3) is applied for the disinfection of drinking water, for the removal of
effluents from wastewater treatment plants in a process called ozonation (or
ozonisation) as well as for the degradation of organic and inorganic pollutants in
wastewater

Ion Exchange
When water is too hard, it is difficult to use to
clean and often leaves a grey residue. (This is
why clothing washed in hard water often retains
a dingy tint.) An ion exchange process, similar to
the reverse osmosis process, can be used to
soften the water. Calcium and magnesium are
common ions that lead to water hardness. To
soften the water, positively charged sodium ions
are introduced in the form of dissolved sodium
chloride salt, or brine. Hard calcium and
magnesium ions exchange places with sodium
ions, and free sodium ions are simply released in
the water. However, after softening a large
amount of water, the softening solution may fill
with excess calcium and magnesium ions,
requiring the solution be recharged with sodium
ions.

Disinfection
The purpose of disinfection in the treatment of wastewater is to substantially
reduce the number of microorganisms in the water to be discharged back into
the environment for the later use of drinking, bathing, irrigation, etc. The
effectiveness of disinfection depends on the quality of the water being treated
(e.g., cloudiness, pH, etc.), the type of disinfection being used, the
disinfectant dosage (concentration and time), and other environmental
variables.

Sludge Treatment
Sludge treatment is the processes used to manage and dispose of sewage sludge produced during
waste water and drinking water treatment. Sludge is mostly water with lesser amounts of solid
material removed from liquid sewage.
Therefore, it is extremely important to properly treat such sludge in order to minimize its
environmental repercussions. Here is a brief overview of the sludge treatment process to help you
gain a better understanding of the treatment techniques and process requirements.
Step 1 – Sludge Thickening
Step 2 – Sludge Digestion
Step 3 – Dewatering
Step 4 – Disposal

Sludge Thickening
The first step in the sewage sludge treatment plan is called thickening. In this step, the sewage sludge is thickened in a
gravity thickener to reduce its overall volume, thus enabling the easy handling of the sludge. Dissolved air flotation is
another alternative that can be used to effectively to thicken the sludge by using air bubbles to allow the solid mass to float
to the top.
Step 2 – Sludge Digestion
After amassing all the solids from the sewage sludge begins the sludge digestion process. This is a biological process in
which the organic solids present in the sludge are decomposed into stable substances. This process also helps reduce the
total mass of solids, while destroying any present pathogens to enable easy dewatering. The sludge digestion process is a
two-phase process.
In the first stage, the dry solid sludge is heated and mixed in a closed tank to enable anaerobic digestion by acid-forming
bacteria. These bacteria hydrolyze the large molecules of proteins and lipids present in the sludge and break them down
into smaller water-soluble molecules, which they then ferment into various fatty acids.
The sludge then flows into the second tank where it is converted by other bacteria to produce a mixture of carbon dioxide
(CO2) and methane, after which the methane is collected and reused to power the digestion tank and generate power
(depending on the quantity retrieved).

Step 3 – Dewatering
After retrieving useful gases and other byproducts, the remaining sludge is then dewatered before final disposal. In most
cases, dewatered sludge usually contains a significant amount of water, as much as 70 percent, in spite of its solidified
state.
Therefore, it is important to dry and dewater the sludge beforehand. While using sludge-drying beds is the most
common way to carry out this process, it is extremely time-consuming and may take weeks before the process is
complete. In order to quicken these processes, waste management plans are also employing solid-liquid separation
devices to carry out this process.
In fact, centrifugation is slowly becoming one of the most preferred methods of dewatering sludge. By passing the sludge
through a centrifuge, it becomes easier to retrieve all the water and enable easier handling of the solid waste in shorter
durations at reduced costs. Other alternatives include the rotary drum vacuum filter and the belt filter press.
Step 4 – Disposal
Once the sludge has been effectively dewatered, it can be buried underground in a sanitary landfill or can be used as a
fertilizer, depending on its chemical composition. In cases where the sludge is too toxic to be reused or buried, you can
simply incinerate the sludge and convert it into ash.
While sewage sludge is usually treated using a standard plan of action, it is extremely important to factor in aspects like
the origin of the sewage, the treatment process used to reduce the sewage to sludge, as well as the possible byproducts
that can be retrieved from it for further use before choosing a sludge treatment plan. This will not only help you optimize
your overall output, but will also help you reduce costs by salvaging useful materials for secondary use before ultimate
disposal.

It's a matter of caring for our environment and for our own health.
To prevent groundwater pollution
To prevent sea shore
To prevent marine life
Protection of public life
To reuse the treated effluent, for agriculture, for groundwater recharge, for
industrial recycle
Solving social problem caused by the accumulation of wastewater.
If wastewater is not properly treated, then the environment and human
health can be negatively impacted.

Health Effects of Sewage.
Life-threatening human pathogens carried by sewage include cholera,
typhoid and dysentery.
Other diseases resulting from sewage contamination of water include
schistosomiasis, hepatitis A, intestinal nematode infections, and
numerous others.
WHO estimates that 1.5 million preventable deaths per year result
from unsafe water, inadequate sanitation or hygiene. These deaths are
mostly young children. Another 860,000 children less than five years
old are estimated to die annually as a direct or indirect result of the
underweight or malnutrition associated with repeated diarrheal or
intestinal nematode infections

Sewage Can be Threated by..
Sewage and wastewater contain bacteria, fungi, parasites, and viruses that can cause intestinal,
lung, and other infections. Bacteria may cause diarrhea, fever, cramps, and sometimes vomiting,
headache, weakness, or loss of appetite. Some bacteria and diseases carried by sewage and
wastewater are E. coli, shigellosis, typhoid fever, salmonella, and cholera.
Fungi such as Aspergillus and other fungi often grow in compost. These can lead to allergic
symptoms (such as runny nose) and sometimes can lead to lung infection or make asthma worse. If
you have other health problems, you may be more likely to get sick from exposure to Aspergillus.
Parasites including Cryptosporidium and Giardia lamblia may cause diarrhea and stomach cramps,
and even nausea or a slight fever. Most people have no symptoms to roundworm (Ascariasis).
Roundworms cause coughing, trouble breathing and/or pain in your belly and blocked intestines.
Viruses such as Hepatitis A cause liver disease. Symptoms of Hepatitis A are feeling tired, having
pain in your belly, being nauseous, having jaundice (yellow skin), having diarrhea, or not being
hungry. The Centers for Disease Control and Prevention (CDC) says sewage workers are not at more
risk of Hepatitis A infection than other workers. If many people in your community have Hepatitis
A, your risk may be higher than usual.

Diagram of Sewage Treatment Process: Sewage passes through
primary, secondary, and tertiary treatment.

Treatment and Recycling of Sewage and Sludge.pptx

Treatment and Recycling of Sewage and Sludge.pptx

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