DESIGN OF A COMPLETE SEWAGE TREATMENT PLANT
Basic data needed
- Average flow
- Peak flow
- Sewerage characteristics
- Influent & effluent BOD @ 20C
- Suspended solids
- pH
- Choice of type of secondary treatment
- Activated sludge process with extended aeration or
- Trickling filters
- Treatment units
- Inlet chamber
- Screen chamber
- Grit chamber
- Aeration tanks for activated sludge treatment
- Secondary clarifier and
- Sludge drying beds
Parameters are listed below
-Peak flow
- Plan dimensions of inlet chamber
-Free board = 1 m
-Size of by-pass chamber by side of inlet chamber
Design of screen chamber
Two number of screen chambers are provided as per sound engineering practice. The flow from the inlet chamber to the screen channels chall be controlled by cast iron penstock gates.
The following assumptions are made
-Shape of bar = M.S. Bars
-Size = 10 mm * 50 mm with 10 mm facing flow
-Clear spacing between bars = 20 mm
-Inclination of bars with horizontal = 80°
-Velocity normal to screen = 0.8 m/s
-Provision of submergence depth = 0.3 m
-Approach velocity of upstream of screen > 0.42 m/s
Design of grit chamber
-Design flow
-Surface loading
-Area required
-Detention time
-Volume
-Liquid depth
-Horizontal velocity
-Storage Volume required
Design of aeration tank
-Number of tanks & average flow to each tank
- Incoming BOD to aeration tank
-BOD left in the effluent
-BOD removed in activated plant
-MLSS should be assumed between 3000 & 5000 mg/l
-F/M ratio should be between 0.18 to 0.12
-F/M = (Q/V) * (Yo/Xt)
Aeration tank dimensions
-Assume depth of 3.5 m and appropriate width (from calculations)
-Check for aeration period or HRT
-Check for volumetric loading
-Check for return sludge return ratio
Aerator sizing
-Check for mixing consideration
Design of secondary clarifier
-Check for weir loading
-Check for solids loading
Return sludge pump house
Design of sludge drying beds
Filtrate pump house and sump
Preliminary Effluent Treatment Plant in India helps to remove gross solids and materials which can be collected from the effluent easily and can clog or damage the pumps and skimmers of primary treatment clarifiers. These are in-organic materials and insoluble organic pollutants that remove gross solids and materials which can be simply gathered from the effluent and can damage or clog the skimmers and pumps of primary treatment clarifiers and all Preliminary treatment include of physical separation techniques by controlling the flow rate of effluent.
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