As per the statutory regulations issued by CPCB, various infrastructures like Apartments, Commercial Construction Projects, Educational Institutions, Townships, and Area Development Projects meeting certain criteria have to install STPs for the treatment of sewage that they produce.
The guideline rules cover aspects regarding the location of STPs, the STP technology to adopt, functioning as well as its maintenance to ensure efficient and safe operation of the machinery.
The Guidelines issued for STPs by CPCB are as follows:
CPCB Guidelines for Sewage Treatment Plants
1. The Technology of STP
The approved STP technologies to go with are-
A. Activated Sludge Process(ASP) (only when above 500 KLD sewage is generated).
B. Membrane Bio Reactor(MBR)
C. Moving Bed Bio Reactor(MBBR)
2. Unit Requirements of STP
STPs have various individual units where different sewage treatment processes occur. The units and their criteria as per the guideline’s requirement are as follows.
2.1. Equalization Tank
Activated Sludge Process(ASP) – Should have a Minimum Holding Period of 8 hours.
Sequential Batch Reactor(SBR) – Same as ASP
Membrane Bio Reactor(MBR) – Same as ASP
Moving Bed Bio Reactor(MBBR) – Same as ASP
2.2. Anoxic Tank
Activated Sludge Process(ASP) – Return activated sludge should be pumped to anoxic tank for denitrification.
Sequential Batch Reactor(SBR) – Not Required
Membrane Bio Reactor(MBR) – Same as ASP
Moving Bed Bio Reactor(MBBR) – Same as ASP
2.3. Aeration Tank
Activated Sludge Process(ASP) – Dissolved Oxygen in an excess of 4 mg/L has to be maintained in the Aeration Tank.
Sequential Batch Reactor(SBR) – Same as ASP
Membrane Bio Reactor(MBR) – Same as ASP
Moving Bed Bio Reactor(MBBR) – Same as ASP
2.4. Membrane Tank
Activated Sludge Process(ASP) – Not Required
Sequential Batch Reactor(SBR) – Not Required
Membrane Bio Reactor(MBR) – Membranes should be replaced regularly as per its manufacturer’s specifications
Moving Bed Bio Reactor(MBBR) – Not Required
2.5. Sludge Holding Tank
Activated Sludge Process(ASP) – Sludge holding should be mandatorily provided for holding excess sludge before its dewatering.
Sequential Batch Reactor(SBR) – Same as ASP
Membrane Bio Reactor(MBR) – Same as ASP
Moving Bed Bio Reactor(MBBR) – Same as ASP
2.6. Final Treated Water Holding Tank
Activated Sludge Process(ASP) – Capacity of the tank should be enough to hold water for 2 days minimum.
Sequential Batch Reactor(SBR) – Same as ASP
Membrane Bio Reactor(MBR) – Same as ASP
Moving Bed Bio Reactor(MBBR) – Same as ASP
2.7. Sludge Drying Bed
Activated Sludge Process(ASP) – Instead of sludge drying bed, horozontal centrifuge system should be used for >500KLD STPs. For <500 KLD STPs, belt press or screw press system should be used.
Sequential Batch Reactor(SBR) – Same as ASP
Membrane Bio Reactor(MBR) – Same as ASP
Moving Bed Bio Reactor(MBBR) – Same as ASP
3. Mechanical Equipment Requirement for STP
There should be clear and easy access to the Bar Screen Chamber and Oil & Grease Chamber of STPs installed. Also, the equipments should be of the submersible type with an easy removal/dismantling option whenever maintenance is required.
Air blowers of STP should have Vibration mounts and acoustic enclosures to reduce the noise pollution.
4. Location of STP
STP should be located under the driveway, play area, or clubhouses, and far away from the residential housings to not cause any nuance to the people living.
Also, STP should not be installed in the basement of any building. Access to the STP room should be from Ground Level or Upper Basement through well-designed walkways or headroom, and not from the lowest basement to avoid nuances that may happen due to rain flooding, smell or sound.
5. Treated Sewage Standards
The sewage treated should meet the following standards.
5.1. pH : 6.5 to 8.5
5.2. BOD5 : <10mg/L
5.3. COD : <50mg/L
5.4. Suspended Solids : <10mg/L
5.5. Ammonical Nitrogen : <5mg/L
5.6. Total Nitrogen : <5mg/L
5.7. Fecal Coliform : <100 MPN/100ml
6. Guidelines for installing sensors
It’s mandatory to install sensors for monitoring sewage parameters like BOD, COD, TSS, flow, and pH.
The CPCB recommended sensor types with their communication protocols are as follows.
6.1. pH – Inline Measurement
Sensor: Ion Selective Glass Electrodes
RS 485 Communication with Modbus
6.2. TSS – Inline Measurement
Sensor: Turbidity to TSS correlation with Nephelometric technique
RS 485 Communication with Modbus
6.3. BOD – Inline Measurement
Sensor: UV-Vis Spectrophotometry & combustion (Double beam with entire spectrum scanning
RS 485 Communication with Modbus
6.4. COD – Inline Measurement
Sensor: UV-Vis Spectrophotometry & combustion (Double beam with entire spectrum scanning
RS 485 Communication with Modbus
6.5. Flow – Inline Measurement
Sensor: Electromagnetic Flow Measurement
RS 485 Communication with Modbus
7. Caution Board at STP
Proper cautionary signboards should be displayed and safety protocols should be followed at the STP locations.
“Danger” Sign Boards should be installed at the STP location for the maintenance personals and the public. And “water not fit for drinking” should also be highlighted at the taps delivering sewage water.
8. Use of Treated Sewage
The treated water should be mandatorily used for toilet flushing purposes that should have a dual plumbing system.
9. Modular Operations of STPs
Modular operation of STPs implies that the STP should be developed/constructed in smaller units so that it can be used as per the load or occupancy of people. In large projects where a higher capacity of STPs required, the occupancy in the initial stages isn’t able to meet the operational criteria of the STP. So, the factor should be considered in the design phase itself.