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  Sewage Treatment Plant
Sewage treatment is the process of removing contaminants from waste water and household sewage, both run-off (effluents), domestic, commercial and institutional. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants. Its objective is to produce an environmentally safe fluid waste stream (or treated effluent) and a solid waste (or treated sludge) suitable for disposal or reuse (usually as farm fertilizer). Using advanced technology it is now possible to re-use sewage effluent for drinking water, although Singapore is the only country to implement such technology on a production scale in its production of NEWater.

Sewage Treatment Plant is a facility designed to receive the waste from domestic, commercial and industrial sources and to remove materials that damage water quality and compromise public health and safety when discharged into water receiving systems.

The Principal objective of waste water treatment is generally to allow human and industrial effluents to be disposed of without danger to human health or unacceptable damage to the natural environment. After biological treatment, water may be recovered by adopting tertiary treatment, that may be used for gardening/ flushing and other utilities. The Compact Package plant is simple to operate, requires minimal maintenance, it requires minimum power, land & consumables for reducing operating cost. These are generally manufactured in MS epoxy coated or Stainless steel / FRP as per the specific need. These compact plant are ideal for hotels, hospitals, holiday resorts, country / golf clubs, schools, housing complexes, national parks & industrial commercial complexes. The advantages of smaller decentralized local units for treatment of communal waste water / sewage especially in area where developing urbanization has to integrate with the environment.

Sewage Treatment Plant can be designed on following technologies:

1. Underground STP based on bioreactor (Biofilters)

2. Mobile containerized STP based on Submersed media aerobic reactor (SMAeR)

3. Compact plant based on Fluidized aerobic reactor (FAeR)

4. Decentralized Sewage Treatment Plant

After biological treatment, water may be recovered by adopting tertiary treatment, that may be used for gardening/ flushing and other utilities. The Compact Package plant is simple to operate, requires minimal maintenance, it requires minimum power, land & consumables for reducing operating cost. These are generally manufactured in MS epoxy coated or Stainless steel / FRP as per the specific need. These compact plant are ideal for hotels, hospitals, holiday resorts, country / golf clubs, schools, housing complexes, national parks & industrial commercial complexes. Sukriti highlight the advantages of smaller decentralized local units for treatment of communal waste water / sewage especially in area where developing urbanization has to integrate with the environment.



Sewage Treatment Plant

Convational STP



Decentralized Sewage Treatment Plant


Domestic waste water treatment plant of any city consists of collection, treatment and disposal. In conventional centralized sewage treatment system, about 80% of the cost is accounted for the collection. The cost of collection of sewage and its conveyance to the terminal point in the large cities s very high. Further, the depth of sewer goes on increasing with the increase of length of sewer line and pumping of the sewage at the intermediate and terminal points requires a lot of energy. In centralized treatment system volume of the sewage becomes very large and the distance of conveyance, as the decentralized sewage treatment plant are generally located outside of the cities, is very long. Further CTS aggravates the environmental problem also, because of large volume of the waste water of the entire city is discharged at one place.

In decentralized sewage treatment system, a balance between the advantages of large scale treatment in terms of economics of scale and individual responsibility for domestic waste water treatment plant can be obtained by providing colony wise / sector-wise treatment system. Responsibility of construction as well as operation and maintenance may be taken up collectively by the residential colonies! builders developers. Specific treatment technology should be selected as per the prevailing ground situation like availability of the land etc. Keeping in mind all these points Sukriti Engineers (P) Ltd. offer decentralized state of the art following package sewage treatment system.
  1. Underground STP based on bioreactor (Biofilters)
  2. Mobile containerized STP based on Submersed media aerobic reactor (SMAeR)
  3. Compact plant based on Fluidized aerobic reactor (FAeR)
After biological treatment water may be recovered by adopting tertiary treatment, that may be used for gardening/flushing and other utilities. The Compact Package plant is simple to operate, requires minimal maintenance, it requires minimum power, land & consumables for reducing operating cost. These are generally manufactured in MS epoxy coated or Stainless steel / FRP as per the specific need. These compact plant are ideal for hotels, hospitals, holiday resorts, country / golf clubs, schools, housing complexes, national parks & industrial commercial complexes.

Sukriti highlight the advantages of smaller decentralized local units for treatment of i i; communal waste water / sewage especially in area where developing urbanization has to integrate with the environment.

STP Design Process

In the previous chapters, the STP units were introduced one by one. This chapter provides the complete design process (calculations) for all units of a typical STP.

In the subsequent two chapters, we will see the engineering and operational aspects of the STP in detail.

STP Design Process



Design process overview

Before starting design, let us review how an extended aeration type STP functions.

1. Domestic sewage is typically pure water that is laden with a small amount of biodegradable pollutants. The STP uses bacteria in the aeration tank23 to digest this biodegradable material. Therefore the incoming sewage must remain in the aeration tank long enough to let the bacteria complete the digestion process.

So the first task before the designer is to retain the sewage long enough in the aeration tank.

2. The bacterial population needs Oxygen to survive.

So the second task before the designer is to provide adequate Oxygen.

3. The bacterial mass (called ?activated sludge?) is recycled and retained in the aeration tank, while the treated water overflows from the clarifier tank. This clarified water is further filtered, disinfected and reused for non-potable purposes (toilet-flushing, washing cars, gardening, etc.). A sizable fraction of treated water remains unused, which is released in nature.

So the third task before the designer is to clarify, filter and disinfect the water.

4. The bacteria breed in the aeration tank, which increases the sludge volume constantly. Secondly, the bacterial population is the most vigorous when average age of the bacteria in the tank is maintained at 25 days. Both these purposes are achieved by bleeding off the excess sludge periodically. (The discarded sludge is used as organic manure).

So the fourth task before the designer is to provide a system for disposal of excess sludge.

The designer starts by estimating the amount of sewage generated. This is the basis for calculating all physical properties of the STP (tank volume, pump capacity, etc.)

Then the designer estimates the amount of nutrition (carbohydrates, proteins, etc) present in the sewage. This is called ?food? (which the bacteria have to digest). For a given type of use (residential/ office/factory) and scale of operation, the amount of food can be estimated with a fair accuracy (using empirical data).

The next step is to find the amount of bacteria needed to digest this amount of food. Based on this figure, the subsystems needed to handle the bacteria are designed (amount of oxygen needed, amount of excess sludge to be handled, etc.).
 
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