Sewage Treatment Plant

Sewage Treatment Plant:

In early 1990, domestic wastewater i.e Sewage was generally disposed of either in pits, open ground or on surface water bodies. Due to increase in population and rapid industrialization, urban development took place resulted in the accumulation of waste in densely crowded habitation/cluster.

In order to protect public health from offensive and injurious substances, it becomes a necessity to treat the domestic wastewater/sewage before letting it into surface streams.

The wastewater treatment system consists of compilation transport and treatment of sewage/wastewater along with its safe disposal. It thus became necessary to establish centralized as well as decentralized domestic sewage treatment plants.

After conveying the domestic wastewater/sewage through secures, the next steps is its disposal, either after treatment or even before treatment.

Sewage Treatment Plant: Process Description

• The outfall sewer main from the last manholes will be let into a screen by gravity flow. Large solids particles shall be intercepted by a 5 mm – 8 mm spacing screen. The screen shall be manually cleaned with suitable rake arrangement.
• The sewage after the screening is collected in a collection sump for smoothing out peak flows. This sump is suitably sized, to accommodate peak flow, as well as breakdown buffer. The provision of the air shall be kept in this tank to break the solids in suspension and to homogenize the sewage.
• The homogenized effluent is then pumped into the Aeration Basin. The air shall be provided through an air diffusion system to ensure equal distribution of air in the reactor.
• The overflow from the Aeration basin is passed through a Settler and collected in Clarified Tank by gravity. From where it is pumped to a pressure sand filter, which is capable of removing finely divided colloidal particles. An activated carbon filter will remove all traces of color and odor and disinfection is done with the help of UV so that the effluent can be used for gardening.
• Filter backwash and sludge filtrate would be taken back into the collection sump.
• Sludge generated in the Settler will be de-watered in a sludge holding tank. This sludge can be used as organic manure and sold as such.
  Excess treated effluent can be discharged into the sewer or can be used as per requirement since it meets PCB requirements.

STP Plant Operation Of Proposed Process:

• Screening:
  Sewage is directed into a bar screen chamber for removal of floating material such as polythene bags etc. A manual coarse-bar-screen is provided for separation, thereby protecting the subsequent process equipment from damage and improving the reliability and effectiveness of the process.
• Oil & Grease Removal:
  Oil in sewage forms scum and can interfere with the biological process. Sewage from bar screens passes through the Oil & Grease Trap for removal of Oil, Fats or other greasy matter from sewage.
• Secondary Treatment:
  • Aeration Tank: – The floating media with attached biomass shall degrade the dissolved BOD with the help of oxygen forced through the blowers. The BOD load is reduced to the extent of recycling for flushing and gardening purpose.
  • Tube Settler: – The settling tank with a media enhances and fastens the settling period of particles to give good quality of water for the tertiary treatment. The biomass separated shall be degraded in the equalization tank; excess shall be feed to Filter press/centrifuge/Filter-bags for dewatering.
  • Disinfection: The purpose of disinfection in the treatment is to substantially reduce the number of micro-organisms in the water. To disinfect the harmful bacteria in the treated water as well as to remove the refractory organics from treated water, UV System is used.
• Pressure Sand Filter (PSF):
  A Pressure Sand Filter is primarily used for the removal of turbidity and suspended solids as low as 10-20 microns. Pressure Sand Filters provide very efficient particle removal under the conditions of a high filtration rate. Inside a Pressure Sand Filter is a layered bed of filter media.
  PSF consists of a composite pressure vessel with frontal piping and manual valves, a top distribution assembly to distribute the Incoming Water uniformly throughout the cross section of the filter & bottom collector assembly to collect Filtered Water. Different layers of Sands are used as the filter media. Under bed supporting media (gravels and pebbles) shall be provided to support the Bottom distribution assembly & Media. Periodically cleaning of PSF is done by backwashing. The backwash of PSF will take place when the differential pressure across bed increases to 0.5 kg /cm2 (g). Water is introduced in the reverse direction of the service flow that is from the outlet nozzle upward causing suspension of the turbid material in the filter bed & finally flushing out through the backwash valve.
• Activated Carbon Filter (ACF):
  PSF treated water shall be fed to the Activated Carbon Filter. Hence it helps to remove odor and color from water. The filters are down-flow; activated carbon filters with constant flow rate control by manually operated valves. When the pressure drop across the filter rises above pre-defined value due to clogging of the bed i.e. pressure drop across the filter will increase, the filters shall be taken for backwashing using water. The backwash of ACF is to be done when the differential pressure across bed increases more than 0.5 kg /cm2 (g). Water is introduced in the reverse direction of the service flow that is from the outlet nozzle upward causing suspension of the turbid material in the filter bed & finally flushing out through the backwash valve. The Filter is then down rinsed & filtered water is used in the system.