The Working Principle of Sewage Treatment Plant (STP)

Firstly, Sewage is a suspension of water and and solid waste, transported through sewer for disposal or treatment. Treatment of sewage or wastewater protects public health and prevents pollution, disease as well as hazards from sewage contaminants. Hence, sewage treatment is required.

Sewage Treatment Plant (STP) process is similar to the way that a Septic Tank works but mechanical components provide additional processes to help break down solids to produce a cleaner, more environmentally friendly effluent.

 

WORKING PROCESS OF A SEWAGE TREATMENT PLANT (STP)

Below is a typical view of a Sewage Treatment Plant (STP) showing all the equipment in the equipment room.

 

[1] THE SEWAGE PASS THROUGH BAR SCREEN

The purpose of the Bar Screen is to prevent by screening any possible particles that can cause blockage to the pipes inside the STP.

All this particles are remove after some weeks when maintaining the STP.

 

[2] THE SEWAGE IS PASS TO AN EQUALIZATION TANK

Equalization Tank main function is to act as buffer. To collect the incoming raw effluent that comes at widely fluctuating rates and position to the rest of the ETP at steady ( Average ) flow rate . During the peak hours ETP comes at high flow rate with the help of Blowers. The equalization tank stores this effluent and lets it out during  the non peak time when there is no /little incoming effluent. The inlet pipe of equalization tank carries filtered effluent to prevent blockage.

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[3] THE SEWAGE IS THEN PUMP TO THE AERATION TANK

The Sewage Lifting Pump, pump the sewage from the Equalization Tank to the Aeration Tank.

Aeration is used in water treatment as a pretreatment in the process of removing iron and hydrogen sulfide (rotten egg smell) from water. Air is a powerful oxidizer of both iron and hydrogen sulfide. It quickly converts unfilterable ferrous iron to filterable ferric iron, and it reduces hydrogen sulfide to elemental sulphur, which is easily removed from water by a filter. Air is a very fast oxidizer–considerably faster than chlorine.

 

[4] THE AERATED WATER IS THEN MOVE TO TUBE SETTLER TANK.

Poly Aluminum Chloride (PAC) is pass into the Tube Settler Tank from the PAC Tank. PAC is Highly efficient coagulant and Good in Low generation of waste sludge.

Tube settlers use multiple tubular channels sloped at an angle of 60° and adjacent to each other, which combine to form an increased effective settling area. This provides for a particle settling depth that is significantly less than the settling depth of a conventional clarifier, reducing settling times.

Tube settlers capture the settleable fine floc that escapes the clarification zone beneath the tube settlers and allows the larger floc to travel to the tank bottom in a more settleable form. The tube settler’s channel collects solids into a compact mass which promotes the solids to slide down the tube channel.

 

[5] THE WATER THEN MOVE TO THE IMMEDIATE STORAGE TANK.

Chlorine is pass into the immediate Storage tank from the Chlorine Dosing Tank

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When chlorine is added for treatment of water, it help in delaying the action of anaerobic sulphate reducing materials, also help I’m reduction of nuisance due to the odour at the sewage work. The chlorine also help in destroying bacteria while still in the Immediate Storage Tank.

 

[6] THE WATER IS THEN PUMP TO THE FILTER FEEDS

The Filter Feed Pump, pump the water to the Pressure Sand Filter.

The Pressure Sand Filter consists of a multiple layer of sand with a variety in size and specific gravity. These Filters are designed to remove turbidity and suspended particles present in the feed water with minimum pressure drop. Then the water move to the Carbon Filter, which are most effective at removing chlorine, particles such as sediment, volatile organic compounds (VOCs), taste and odor from water. They are not effective at removing minerals, salts, and dissolved inorganic compounds (DOCs)

Typical particle sizes that can be removed by carbon filters range from 0.5 to 50 micrometres. The particle size will be used as part of the filter description. The efficacy of a carbon filter is also based upon the flow rate regulation. When the water is allowed to flow through the filter at a slower rate, the contaminants are exposed to the filter media for a longer amount of time.

[7] THE WATER THEN MOVE TO THE TREATED WATER TANK

This is the final destination for the water, where the water will be distributed for either domestic use or industrial use, Depending where the Sewage Treatment Plant is Located.

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[8] THE SLUDGE IS FINALLY MOVE TO THE SLUDGE HOLDING TANK

Sludge is a bi-product from treatment of wastewater at any traditional wastewater treatment plant, and while treated water can be discharged to the receiving waters according to the requirements in the discharge permit, handling sludge treatment is more complicated. Generally, final disposal will be utilisation as fertiliser on farmland, deposition at waste disposal sites, or incineration onsite or at an external partner, often as part of energy generation.

Sludge pumping requires equipment that can keep viscous media moving – without becoming clogged. Primary sludge needs to be pumped from Tube Settler Tank to the sludge Holding Tank for its final Disposal or can even serve as Fertilizer on Farmland as mentioned above.

 

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3 Replies to “The Working Principle of Sewage Treatment Plant (STP)”

  1. Hi Cornelius,
    Thanks for bringing such simplified explanation for working of STP.
    Kindly share me the PDF version for this, as I am unable to get the same.

    Also, try to roll out akin presentation for working of Effluent Treatment Plant, as well.

    Regards,
    Pavan Sharma

      1. hello sir,

        Thanks to you for essely describing STP working process,

        Also i am interesting in design of size of tank, filter meading, size of pump with piping meance what design parameters considered for that.

        please provide STP working process in PDF and as well as design.

        thanks ,
        prabhakar Bhoir

        prabhakar.bhoir@amanora.com

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