In many rural and urban areas in India, there is not much awareness about environmental conservation and this is the reason they have either rudimentary sewage treatment facility or no system at all. Surprisingly in large number of Indian localities, raw sewage is simply discharged in the rivers or ocean without treating. Well if it is discharged in regularly and constantly in flowing stream then the possibility of self-purification is longer but if it is discharged in conserved or preserved water resources then it surely pollutes the water source as well the environment.

1. Sewage Water
Sewage water is normally all the water that is generated after routine household use like washing, toilet,
bathing, cleaning etc. In many of the Indian cities rainwater and even industrial wastewater enters the
street drains of sewage system. More often sewage water consists of large amount of water and only little
percentage of particulate matter. However if we consider the amount of sewage water generated in large
cities then the solid portion present in this water is more than 1000 tons per day.
Still in many rural and urban areas in India, there is not much awareness about environmental
conservation and this is the reason they have either rudimentary sewage treatment facility or no system at
all. Surprisingly in large number of Indian localities, raw sewage is simply discharged in the rivers or
ocean without treating. Well if it is discharged in regularly and constantly in flowing stream then the
possibility of self-purification is longer but if it is discharged in conserved or preserved water resources
then it surely pollutes the water source as well the environment.
Sewage Treatment in India
It is considerably, clear that sewage treatment plants are not present everywhere in Indian villages and
cities. Therefore, considering the few those are present in metro cities and are functioning appropriately it
is useful to understand type of method used in such sewage treatment plants.
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Primary Sewage Treatment
This is primary phase of sewage water treatment wherein large floating material present in the incoming
sewage water is filtered. Using precise careening procedure sewage water is allowed to flow through
settling chambers. Material such as floating oil, grease, floating debris and other particulate is removed in
this phase. Then sewage passes through sedimentation tanks allowing more solid matter to settle down
thus this collected material at the bottom is called sludge. Usually 60-70% of solid particulate present in
sewage is removed in this process, sometimes to accelerate the process of settling treatment different
flocculating chemicals are used. At the end of this phase, the sludge thus formed is removed or collected
on a regular basis and the effluent water is allowed to pass through the secondary phase of sewage
treatment.

Secondary Sewage Treatment

2. After the effluent sewage enters the second phase of treatment most of the remaining material constitutes
dissolved organic matter. In most of the sewage treatment plants secondary treatment is predominantly
biological and is carried out to remove dissolved organic matter. Aeration is the first process enhancing
the growth of aerobic bacteria as well other microorganisms that eventually help in dissolving organic
matter in to carbon dioxide and water. As of now, the most commonly used secondary sewage treatments
in India are activated sludge system and trickling filters.
Sewage treated in secondary phase is usually disinfected using chlorination procedure before it is
discharged, most of the times this treated sewage is discharged in ocean or in a flowing stream but in
some cities, it is also used to spray irrigation fields. It is good to mention that in some Indian cities sewage
is treated to such an extent of purity that it can be used as drinking water.
Activated Sludge Process

Tertiary Sewage Treatment
Having understood primary and secondary sewage treatment methods in detail not in every aspect these
processes are elaborate enough to remove all the biologically degradable organic matter. It does not

3. matter if less than excessive organic matters are released in to flowing stream, as they do not cause any
serious damage to the environment or water. However, in cities where the pressure of creating waste
above the flowing waters carrying capacity is generated and in cities where treated sewage is discharged
in lakes, tertiary sewage treatment plants have came in to existence.
In this phase of sewage treatment residual BOD (Biochemical Oxygen Demand), nitrogen and
phosphorous having potential to affect stable waters ecosystem are entirely removed. This treatment is
more biological, than physical or chemical treatment achieved in the previous phases. Usually tertiary
sewage treatment is more costly but has ability and efficiency to treat water to the extent of making it pure
for drinking purposes.