Municipal waste water treatment. .pdf

Waste

1. Municipal Wastewater
Treatment
Submitted by
Sreya PS
M.Sc Food technology

2. ◦Municipal wastewater treatment is the process of removing contaminants from
wastewater generated by households, business, and industries before releasing it
back into the environment.
◦It involves several stages
➢Primary treatment
➢Secondary treatment
➢Final treatment

3. Primary Treatment
◦Primary treatment meant for removing the total solids in sewage by sedimentation
◦Raw sewage contain two types of solid materials; coarse solid materials and
settleable solid materials
◦Coarse solid materials are removed by screening, grit chambers grinding
◦Settleable solid materials are removed by holding the sewage in sedimentation
units. Eg; Tanks and basins

4. Secondary Treatment
◦The process in which the effluent is exposed to a massive culture of
microorganisms under aerobic conditions
◦This method is biological in nature because stabilization or mineralization of
putrescible matter takes place through the microbial agency
◦METHODS
1. Biofiltration
oIntermittent sand filters
oTricking filters
oContact filters
2.Aeration by the activated sludge process or by contact aerators
3. Lagoons

5. Intermittent sand filters
◦It consists of bed of sand about 2 ½ to 4 feet deep, with drains at the bottom
◦The effluent is applied to a depth of 3 to 4 inches over the whole area of bed
◦The sand particles get coated with the suspended putrescible matter and large
numbers of microorganisms during sewage filtration
◦Microorganisms present in a gelatinous sand coating oxidize sewage solids as well
as the dissolved matter during the seeping of sewage through the coated sand
◦Sewage is applied intermittently over the sand bedand this is the reason why this
method is known as intermittent sand filter method

6. Contact filters
◦Contact filters consists simply of tanks filled with crushed gravel, slag and the
depth of bed is 4 to 6 feet which is equipped with underdrains
◦The effluent from a sedimentation tank or imhofftank is applied over the contact
bed. The sewage is permitted to stand for an hour or two
◦The suspended solids and putrescible materials are retained by the rocks. These
rocks are the micro-first few loads with a film f stalked becteria, other bacteria ,
water-mouldsand protozoa and they are involved in the degradation of the
putrescible matter
◦The effluent is then drawn off, and air is drawn in

7. ◦This produces active aerobic degradation, andis permitted to continue for several
hours. Then the process is repeated
◦If properly handled up to 90% of the solids and 80% of the BOD will be
removed
◦This method is not widely employed at present because its capacity is relatively
low, compared with some other methods

8. Trickling filters
◦The trickling filter has been designed on the basis ofexperiments carried out at
the Lawrence experiment station in 1894
◦It consists of a bed of coarse pieces of stone, gravel and slag or related material.
The depth of the bed is 1 to 3 inches, this leaves a great many open spaces in the
bed for the penetration of air
◦The tank is equipped with drains underneath. These filters have been described as
a pile of rocks over which sewage or organic wastes slowly trickle
◦The liquid sewage is applied over the surface of the bed

9. ◦The application of the effluent is made, either from fixed pipes or from rotating
metal pipes with holes at intervals along the pipe. Such a practice of spraying
saturates the effluent with oxygen.
◦The effluent is allowed to trickle through.
◦Bacteria oxidize the organic compounds present in the seeping sewage
◦After the biodegradation of the effluent new cells formed. These cells exert a
high BOD and must be removed before the effluent is finally discharged to a
natural body of water
◦This is accomplished in secondary sedimentation tanks. It is required to build up a
coating of microbial flora. This is achieved by operating the filter over a period of
a few weeks
◦Extensive growth of algae in the upper part is objectionable because it impairs
the operation of the trickling filter.

10. Activated sludge process
◦The process is based on vigorous aeration of that is vigorously aerated. This
results in more rapid flocculation
◦The finer particles clump into flocs. Such flocs are allowed to settle and then
added to fresh sewage station
◦The process is repeated to bring about quick and complete flocculation of the
fresh sewage
◦The final sludge thus formed contains some inert solids and living bacteriasand
protozoa. Thereforethis process is referred to as the activated sludge process
◦These microorganisms carry out appreciative oxidation of organic matter, and
thus BOD is reduced

11. Lagoons
◦Lagoons are also known as oxidation ponds or stabilization ponds
◦It is the most important method of sewage treatment in hot climate where
sufficient land is normally available
◦The preliminary treatment to the sewage is given to remove most of the solids.
The sewage effluent resulting from the preliminary treatment stage is dumped
into a large pond having a depth of 2 to 4 ft
◦lagoonizationis a natural process of sewage purification because oxidation of
putrescible matter occurs through symbiotic action of algae and aerobic bacteria
present in the effluent.

12. Final Treatment
◦Organic matter remaining after sludge digestion is stabilized and is not easily
decomposed further. It is black and without any appreciable odour. Stabilized
sludge may be dried and sold as a fertilizeror it may be burned
◦The effluent is chlorinated and is generally dumped into some water channel for
final disposal
◦Satisfactory chlorination can kill the bacteria more than 99% of the original
bacterial population

13. Disposinginfinaltreatment
◦The final disposal of municipal wastewater typically involves several methods to
ensure environmental safety and compliance. Here are some common approaches
◦Land application : Treated wastewater is discharged onto land for irrigation r
recharge of groundwater, where soil and vegetation further filter and treat the
water
◦Discharge to surface water : treated effluent may be discharged into rivers, lakes
or oceans after meeting specific regulatory standards to prevent harm to aquatic
life and public health
◦Reuse :increasingly, treated wastewater is being reused for purposes such as
irrigation, industrial processes and even potable water supply after advanced
treatment

14. THANK YOU
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