Chapters :


About 85% of the suspended solids and BOD can be removed by a well running plant with secondary treatment. Secondary treatment technologies include the basic activated sludge process, the variants of pond and constructed wetland systems, trickling filters, rotating biological contactors and other forms of treatment which use biological activity to break down organic matter. The existing treatment systems can also be modified so as to broaden the capabilities and performance. 

Disinfection: The disinfection typically with chlorine can be the final step before discharge of the effluent. However, some environmental authorities are concerned that chlorine residuals in the effluent can be a problem in their own right, and have moved away from this process. Disinfection is frequently built into treatment plant design, but not effectively practiced, because of the high cost of chlorine, or the reduced effectiveness of ultraviolet radiation where the water is not sufficiently clear or free of particles.

Tertiary treatment (to enhance to water quality):

The purpose of tertiary treatment is to provide a final treatment stage to raise the effluent quality to the desired level by removing more than 99 per cent of all the impurities from wastewater, producing an effluent of almost drinking-water quality. This advanced treatment can be accomplished by a variety of methods such as coagulation sedimentation, filtration, reverse osmosis, and extending secondary biological treatment to further stabilize oxygen-demanding substances or remove nutrients. In various combinations, these processes can achieve any degree of pollution control desired. As wastewater is purified to higher and higher degrees by such advanced treatment processes, the treated effluent can then be reused for urban, landscape, and agricultural irrigation, industrial cooling and processing, recreational uses and water recharge, and even indirect and direct augmentation of drinking water supplies. 

Coagulation- Sedimentation Chemical coagulation sedimentation is used to increase the removal of solids from effluent after primary and secondary treatment. The solids heavier than water settle out of wastewater by gravity in the primary and secondary sedimentation tanks but the lighter particles are made to settle down with the addition of specific chemicals, like alum Al2(SO4)3, lime (CaO), or ferric salts of iron (Fe3+ ). With the addition of these chemicals, the smaller particles clump or ‘floc’ together into large masses. The larger masses of particles will settle out in the sedimentation tank reducing their concentration in the final effluent.

Filtration- Sand filtration, which consists of simply directing the flow of water through a sand bed, is used to remove residual suspended matter. Filtration over activated carbon results in the removal of: non-biodegradable organic compounds, absorbable organic halogens, toxins, dyes etc. Membrane filtration is a process which relies on a liquid being forced through a filter membrane with a high surface area and small pore size to remove bacteria, viruses, pathogens, metals, and suspended solids. 

Reverse osmosis

– In the reverse osmosis process, pressure is used to force effluent through a membrane that retains contaminants on one side and allows the clean water to pass to the other side. Reverse osmosis is actually a type of membrane filtration called microfiltration because it is capable of removing much smaller particles including dissolved solids such as salt.

Nutrient Removal:

The nutrients in the form of Nitrogen and Phosphorus present in the treated water causes eutrophication and hence have to be removed. The nitrifying bacteria. are employed for removal of ammonia present in wastewater. These bacteria can biologically convert ammonia to the non-toxic nitrate through a PROCESS KNOWN AS NITRIFICATION.

The nitrification process is normally sufficient to remove the toxicity associated with ammonia in the effluent but the product formed nitrate is a nutrient and in excess amounts can contribute to eutrophication in the receiving waters. 

In such situations where nitrogen must be completely removed from effluent, an additional biological process can be added to the system to convert the nitrate to nitrogen gas. The conversion of nitrate to nitrogen gas is accomplished by denitrifying bacteria in a process known as DENITRIFICATION. Effluent with nitrogen in the form of nitrate is placed into a tank devoid of oxygen, where carbon-containing chemicals, such as methanol, are added. In this oxygen-free environment, bacteria use the oxygen attached to the nitrogen in the nitrate form releasing nitrogen gas and it is used for other processes like biogas etc.  Therefore in such a manner the waste water can be treated and reused. 


Waste is defined as any unwanted or unusable substance that is discarded after primary use. Wastes are normally generated as a result of human and animal activities. Urbanization and rapid advancements in industrialization has led to an increase in the production and consumption processes resulting in the generation of wastes from various sectors that include Agricultural, Commercial, Domestic, Industrial, And Institutional and from community activities. Over time, these wastes accumulate and can have real impacts on the health and the environmental degradation. The problem of waste accumulation is becoming unmanageable with issues like Landfills, Solid Waste, Heaps Of E –Waste Trade, River Collaging And Marine Garbage Patches. Hence Waste management is intended to reduce adverse effects of waste on health, the environment or aesthetics. The main three principles reduce, reuse and recycle is the key to approach the environmental issue of waste management. 


The waste generated from various sources is classified based on their properties eg. Solid, Liquid And Gaseous. They are also classified based on their sources, like municipal waste, agricultural waste, biomedical waste etc. broadly from the environmental angle it is classified as biodegradable and non-biodegradable. 


SOLID WASTE- solid wastes include Waste Tires, Septage, Scrap Metal, Latex Paints, Furniture And Toys, Garbage, Appliances and vehicles, oil and anti-freeze, empty aerosol cans, paint cans and compressed gas cylinders, construction and Demolition Debris, Asbestos, Plastics, Styrofoam Containers, Bottles etc. 


Liquid wastes can be defined as liquids/fluids that are generated from washing, flushing or manufacturing processes of the industries. They are also called as Sewage. Examples: domestic washings, chemicals, oils, waste water from ponds, Wastewater from manufacturing industries, manure, waste oil, fats, oils or grease (FOG), used oil, and hazardous household liquids.

Gaseous waste

It is a waste product released in the form of gases from automobiles, factories, industries, burning of fossil fuels etc and gets mixed in the atmosphere. These gases include Carbon Monoxide, Carbon Dioxide, Sulphur Dioxide, Nitrogen Dioxide, Ozone and methane etc.

Municipal solid waste 

Municipal solid waste (MSW) Municipal solid waste commonly referred to as trash, garbage or refuse comprises of street wastes, dead animals, market wastes, abandoned vehicles, household garbage, rubbish, construction and demolition debris, sanitation residue, packaging materials, trade refuges etc. They are collected from residential houses, markets, streets and other places mostly from urban areas and disposed of by municipal bodies. It is among the largest source of several types of pollution and landfill problems and necessitates

Management Strategy – segregation at source, recycle, faecal sludge management, sewage treatment and safe disposal.


It is large amount of waste generated from the industrial activities. Some examples of industrial wastes are chemical solvents, paints, sandpaper, paper products, industrial by-products, metals, and radioactive wastes. Industrial solid wastes are further classified as hazardous and non-hazardous wastes. These are very hazardous and have to be treated mandatorily before letting into the nature.


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