Wastewater TreatmentBY SUSHIL KUMAR

What is wastewater ?

Water that has been utilized in some capacity that negatively impacts the quality of water.

Sewage is a subset of wastewater that is contaminated with feces or urines.

Where does wastewater come from?

Residences (kitchen, bathroom) Rainfall, Highway drainage Industrial institution

Wastewater Constituents

Water (more than 95%) Pathogens (bacteria, viruses and parasitic worms) Non-pathogenic bacteria Organic particles(feces, hair, food, paper fiber, plant materials) Soluble organic (urea, protein, sugar ,drug) Inorganic particles (sand, grit, metals, ceramics etc.) Soluble inorganic (ammonia, hydrogen sulfide, thiosulfates

etc.) Toxins (pesticides, poisons, herbicides etc.)

What is wastewater treatment?

process of removing contaminants from wastewater, both runoff and domestic and making it suitable to discharge back into the environment.

Municipal wastewater treatment

Industrial wastewater treatment

How can we say water is pure?

Physically

a) Total solid (tested by boiling water)

b) Odors

c) Colors

d) Turbidity Chemically

a. Biological oxygen demand (BOD)

b. Chemical oxygen demand (COD)

Methods involved in wastewater treatment

Wastewater Treatment Mechanical (Physical) Treatment

a) Preliminary

b) Primary Secondary (Biological) Treatment Tertiary (Chemical) Treatment Sludge Treatment

Preliminary Treatment

The objective of preliminary treatment is the removal of coarse solids and other large materials often found in raw wastewater.

Removal of these materials is necessary to enhance the operation and maintenance of subsequent treatment unit.

Coarse Screening Grit Removal

Coarse Screening

Removal of large non biodegradable and floating solids (e.g. rags, clothes, woods, plastics, papers etc.)

Grit Removal

Grit particles which are smaller than the aperture of the coarse screen will pass through and may cause abrasive problems to pipes and pumps.

In grit removal process, velocity is so controlled that grit may settle but most of the organics are retained in suspension.

Primary Treatment

Objective is the removal of settelable organic and inorganic solids by Sedimentation, and the removal of the material that will float (scum) by skimming.

Around 25-50% of the incoming BODs, 50-70% of the total suspended solids and 65% of oil and grease are removed during primary treatment.

Secondary Treatment

Biological Treatment

• Secondary treatment is designed to substantially degrade the biological content of the sewage which are derived from the human waste, food waste, soaps and detergents etc.

• Aerobic bacteria and protozoa consume biodegradable soluble organic contaminants (e.g. sugar, fats, short chain carbon molecules etc.) and binds much of the less soluble fractions into floc.

Secondary sedimentation

• Microorganisms must be separated from the treated water by sedimentation to produce clarified secondary effluent.

• Biological floc is settled out in secondary clarifier and the secondary sludge is then sent to sludge treatment unit.

Nutrients Removal

Wastewater may contain high level of nutrients (N or P compounds) which excessive release to environment may cause eutrophication.

Overgrowth of weeds, algae, blue-green algae (cyanobacteria).

DE oxygenation Toxins produced by some algae may

contaminate drinking water supply.

Nitrogen Removal

Nitrification

• Biological oxidation of nitrogen from ammonia to nitrate.

I. Ammonia to nitrite using Nitrosomonas

II. Nitrite to Nitrate using Nitrobacter ssp. DE nitrification (anoxic condition)

• Nitrate is converted into nitrogen gas and released into air.

Phosphorus Removal

Biologically• Using Polyphosphate Accumulating Organism (PAOs)

• The process is called “Enhanced biological phosphorus removal”.

By chemical precipitation• Using salts of irons (e.g. ferric chloride) or

aluminium (e.g. alum) or lime.

Tertiary Treatment

Purpose is to provide a final treatment stage to further improve the effluent quality before it is discharged to the receiving environment.

Nutrients removal Disinfection

• to reduce the number of microorganisms Chlorination Ultraviolet radiation Ozone Odor control

Odor Control

Odor emitted by wastewater treatment are typically an indication of anaerobic or septic condition.

Generally arises due to hydrogen sulfide. Controlled by adding iron salts or hydrogen

peroxide or calcium nitrate.

Sludge Treatment

This process describes the management and disposal of primary and secondary sludge.

processes involved are Anaerobic digestion Composting De watering

Anaerobic Digestion

Anaerobic bacteria acts on sludge and produces large amount of waste solids and biogas ( high concentration of methane).

Methane can be used to generate electricity and run few pumps.

Solid waste (containing water) is sent for composting.

Composting

An aerobic process that involves mixing of wastewater solids with sources of carbons such as sawdust, straw or woodchips.

Aerobic bacteria digests both wastewater solids and carbon source and produce large amount of heat.

Resultant solid is then sent for dewatering.

DeWatering

Water is removed from solid waste for volume reduction.

Using drying beds Mechanically filtering often through cloth screens. Centrifugation.

The sludge is now ready to be used off sites as fertilizers.