Sewage Treatment Plants ( STP Process )

 
Sewage Treatment Plant ( STP Process )



The following process description and schematic flow diagram will assist in the understanding of the treatment processes used for the Wastewater Treatment Plant.
   
The Wastewater Treatment Plant is divided into five principal chambers;
   
 
Anaerobic chamber - anaerobic treatment
 
Aerobic chamber - aerobic treatment
 
Clarification chamber - sludge settlement and removal
 
Disinfection chamber - contact time with chlorine
 
Pumpout chamber - discharge to disposal system
   
Anaerobic Chamber
 
Raw wastewater is initially received into the anaerobic chamber. Approximately 30 ‑ 50% of the suspended solids settle out in this chamber where they undergo anaerobic digestion. The anaerobic digestion process is carried out by microorganisms which have the ability to feed, grow and multiply in the absence of free oxygen.  In addition, settled sludge and skimmed material returned from the clarification chamber are further digested in this chamber.  The plant is sized to enable these microorganisms to maintain a sufficient population naturally without the need for the addition of proprietary biological products.
 
Aerobic Chamber
 
The partially treated wastewater, still containing the colloidal and dissolved solids which represent approximately 65% of the pollution loading, flows from the anaerobic chamber to the aerobic chamber.  Air is introduced to the liquid in this chamber by means of a compressor and diffusers, maintaining aerobic (free dissolved oxygen) conditions.  The oxygen enriched effluent flows about packs of submerged media having a large surface area on which bacteria and other microorganisms thrive, forming a biological film.  These microorganisms have a different growth process to those in the anaerobic chamber in that they utilise the dissolved oxygen in the effluent, while consuming the dissolved and colloidal organic matter as food to create new cell growth and stable oxidised products.  The air pattern causes the liquid in the chamber to pass through the media in a discreet flow pattern and to have intimate contact with the microorganisms.
 
The process differs from ordinary suspended growth systems in that it is more stable and also allows the growth of sub-surface anaerobic microorganisms beneath the surface film of aerobic microorganisms. This allows anaerobic bacterial action to check the media growth, thereby reducing the biological sludge accumulation. Nevertheless, as the thickening of material on the media occurs, some sloughing off will take place.
 
The multiple compartment design of the aerobic chamber ensures that no short-circuiting can occur, preventing the possibility of partially treated wastewater passing to the clarification chamber.  The diffused aeration system allows the air to be introduced below the media packs.
 
Basically the reaction in the aerobic chamber converts the dissolved and non‑settle able (colloidal) solids into carbon dioxide and a biological floc, which, under quiescent conditions, will settle.
 
Clarification Chamber
 
Following aeration, effluent flows into a circular hopper bottomed clarification chamber, where the biological floc (or sludge) settles under quiescent conditions.  Settled sludge from the bottom of the chamber and floating material are returned to the anaerobic chamber. From the clarification chamber, the effluent is drawn off below surface level and flows through the chlorinator to the disinfection chamber.
 
This continuous return of sludge to the anaerobic chamber ensures continuous fluid movement in the plant even with zero inflow and keeps the system "live" during periods of extended vacancy
 
Disinfection Chamber
 
The discharge from the clarification chamber passes through an automatic gravity chlorinator.  The chlorinator is calibrated for above normal water usage.  Chlorine stocks are provided to cover maximum usage with built in safety factors to cover all foreseeable circumstances between the service periods.
 
The disinfection chamber is designed to provide a minimum of 30 minutes contact time between the effluent and chlorine to ensure achievement of bacterial die-off
 
Pumpout Chamber
 
After disinfection, the treated effluent enters the pumpout chamber.  The submersible pump in this chamber is automatically controlled by a level switch to operate and shut down as the level of the effluent rises and falls.
 
BIOCULTURE FOR SEWAGE TREATMENT
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THE BIOCULTURE SHOULD BE USED IN PRIMARY SETTLING TANK WHERE RETENTION TIME IS MINIMUM 1.5 HOURS.
OUR 1 LITRE PLASTIC CAN, WHICH CONTAINS BIOCULTURE, SHOULD BE PLACED IN A RAW SEWAGE TANK.
AFTER APPLICATION OF CAN, FOR FIRST SIX HOURS RAW SEWAGE FLOW SHOULD BE STOPPED AND AFTERWARDS RESTARTED.
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3. NO CHEMICALS
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