Objective for Effluent Treatment Plant Operation
The purpose of this SOP is to establish a clear procedure for the operation, routine monitoring and recording of activities associated with the Effluent Treatment Plant (ETP).
The procedure is intended to ensure that industrial effluent is properly collected, treated and monitored before its final reuse or discharge. It also helps maintain stable plant performance, effective biological treatment, proper sludge management and compliance with applicable environmental requirements.
Scope
This SOP applies to the operation and routine monitoring of the Effluent Treatment Plant installed at the manufacturing facility.
It covers the major stages of treatment, including:
- Collection and equalization of effluent
- pH correction and chemical dosing
- Flocculation and clarification
- Biological treatment
- Sludge recycling and wasting
- Secondary clarification
- Sand and activated carbon filtration
- Treated water collection and reuse
- Sludge dewatering
- Daily testing and documentation
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Responsibility
Engineering Department – Executive/Officer
- Ensuring that the ETP is operated according to this SOP.
- Monitoring the overall performance of the treatment system.
- Reviewing ETP operating parameters and records.
- Ensuring that equipment is available and maintained in operating condition.
- Reviewing abnormal conditions and taking appropriate corrective action.
ETP Operator
- Operating the ETP during the assigned shift.
- Monitoring important operating parameters.
- Maintaining chemical dosing as required.
- Checking aeration, pumps, filters and other equipment.
- Recording daily operating data.
- Reporting abnormalities to the Engineering Department.
- Carrying out routine testing as instructed.
- Maintaining the ETP area in a clean and safe condition.
Procedure for Effluent Treatment Plant Operation
The ETP shall be operated by the designated operator during each shift. All important operating activities, observations, chemical consumption and test results shall be entered in the Daily ETP Performance Report.
The treatment process shall generally be carried out in the following sequence.
Collection of Industrial Effluent
Effluent generated from the manufacturing area is collected through the factory effluent drainage system and transferred to the Equalization Tank (ET).
The Equalization Tank acts as a collection and balancing point. It helps reduce sudden variations in effluent flow, pH and pollutant concentration before the effluent enters the subsequent treatment stages.
Operation of Equalization Tank
Air shall be supplied to the Equalization Tank through the installed aeration grid.
Aeration shall be maintained to:
- Keep suspended solids in circulation.
- Minimize settling of solids.
- Reduce the possibility of anaerobic conditions.
- Maintain relatively uniform effluent characteristics.
The operator shall ensure that the aeration system is functioning properly and report any abnormal noise, vibration or reduction in air supply.
Transfer to Flash Mixing Tank
Effluent from the Equalization Tank is transferred to the Flash Mixing Tank.
Lime is dosed into the tank for pH adjustment. The maximum feed rate shall be maintained as per the approved operating condition, with the specified maximum feed rate being 2.0 m³/hr.
Lime dosing shall be adjusted to bring the effluent pH to approximately 9.5, or to the approved operating range established for the ETP.
The operator shall monitor the pH after chemical dosing and adjust the dosing rate whenever required.
Flocculation and Chemical Dosing
The chemically conditioned effluent then enters the Flocculator.
Alum and polyelectrolyte are dosed to promote the formation of flocs. Proper mixing and chemical dosing are important for efficient removal of suspended and colloidal matter.
The pH of the effluent leaving this stage shall generally be maintained between 6.5 and 8.0, unless a different range is specified in the approved plant design or environmental requirement.
The operator shall observe the floc formation and report any unusual change in floc size, settling characteristics or effluent appearance.
Tube Settler Operation
The flocculated effluent flows to the Tube Settler.
The formed flocs settle at the bottom of the Tube Settler, while the clarified liquid moves upward and overflows toward Aeration Tank-I (AT-I).
The settled sludge shall be removed periodically and transferred to the Sludge Sump.
The pH of the Tube Settler overflow shall be checked and maintained within the specified operating range of 6.5–8.0.
Biological Treatment in Aeration Tank-I
The clarified effluent enters Aeration Tank-I (AT-I) for biological treatment.
In this tank, microorganisms are maintained under aerobic conditions. These microorganisms utilize biodegradable organic matter present in the effluent, thereby reducing the organic load.
Continuous oxygen supply is essential for satisfactory biological treatment.
Surface Aerator
The installed Surface Aerator (SA-I) supplies oxygen to the Aeration Tank-I.
The Surface Aerator shall normally remain in operation continuously, unless shutdown is required for maintenance or an approved operational reason.
The operator shall check:
- Proper operation of the aerator.
- Abnormal noise or vibration.
- Adequate mixing.
- Any unusual foam formation.
- Overall condition of the aeration tank.
Maintaining MLSS in Aeration Tank-I
The Mixed Liquor Suspended Solids (MLSS) concentration in AT-I shall be maintained within the established operating range.
The specified operating range for the plant is:
MLSS: 2500–6000 mg/L
MLSS is controlled by recycling suitable quantities of activated sludge from Secondary Clarifier-I (SC-I) back to AT-I and by wasting excess sludge to the Sludge Sump.
The operator shall monitor MLSS regularly and adjust sludge recycling or wasting according to the operating condition.
Nutrient Addition
Adequate nutrients are required for healthy biological activity.
Where required, nutrients such as:
- Urea
- DAP (Diammonium Phosphate)
- GUR/Jaggery
may be added to AT-I according to the effluent feed rate, biomass condition and approved ETP operating practice.
Chemical addition shall be controlled based on plant requirements and should not be carried out indiscriminately.
Secondary Clarifier-I
The mixed liquor from Aeration Tank-I flows by gravity to Secondary Clarifier-I (SC-I).
The purpose of the secondary clarifier is to separate biological solids from the treated liquid.
The biomass settles at the bottom of the clarifier, while the clarified supernatant overflows through the outlet launder.
A portion of the settled sludge is returned to AT-I to maintain the required biomass concentration.
Excess sludge is periodically transferred to the Sludge Sump.
The operator shall monitor the clarifier for:
- Proper sludge settling.
- Floating sludge.
- Excessive foam.
- Sludge carryover.
- Uneven flow.
- Abnormal turbidity in the overflow.
Transfer to Aeration Tank-II
The clarified effluent from the outlet launder of SC-I flows to Aeration Tank-II (AT-II) as provided in the ETP process arrangement.
The operator shall ensure that the flow path remains clear and that the tank and associated equipment are functioning normally.
Filtration of Treated Effluent
Treated water from the Filter Feed Sump is pumped through the following filtration system:
- Multi Grade Filter (MGF)
- Activated Carbon Filter (ACF)
The Multi Grade Filter removes remaining suspended particles, while the Activated Carbon Filter assists in reducing residual organic matter, colour and objectionable odour.
The operator shall monitor filter performance and carry out backwashing whenever required according to the approved operating schedule or pressure differential.
Backwashing of MGF & ACF
Raw water shall be used for backwashing of the Multi Grade Filter and Activated Carbon Filter, as applicable to the installed system.
The backwash effluent shall be routed back to the designated equalization/collection tank, identified in the plant arrangement as EQ-II.
The operator shall ensure that backwash valves are operated correctly and that there is no leakage or abnormal flow during the operation.
Treated Water Tank
After filtration, the treated effluent is collected in the Treated Water Tank.
The tank shall be monitored for:
- Water level
- Appearance of treated water
- Pump operation
- Overflow condition
- Any abnormal odour or colour
Cooling Tower and Boiler Blowdown
Cooling tower and boiler blowdown streams shall be routed to the Treated Water Tank as per the approved plant piping arrangement.
The operator shall ensure that the designated lines and valves are maintained in proper operating condition.
Reuse of Treated Effluent
The treated effluent is pumped for gardening or other approved reuse applications within the factory premises.
The quantity of treated effluent used for gardening shall be monitored through the flow meter installed on the discharge line.
The operator shall record the quantity of treated water reused in the daily ETP record.
Daily Monitoring and Testing of Treated Effluent
In-house testing of treated effluent shall be performed on a daily basis before final discharge or approved reuse.
The required parameters shall be tested using approved methods and recorded in the designated ETP test record.
Typical parameters include:
- pH
- Total Dissolved Solids (TDS)
- Total Suspended Solids (TSS)
- Chemical Oxygen Demand (COD)
- Biochemical Oxygen Demand (BOD)
Additional parameters shall be tested whenever required by the applicable environmental consent, regulatory requirement or approved monitoring plan.
Important: The acceptance limits used in the current SOP should always be verified against the facility’s latest consent conditions and applicable requirements of the concerned State Pollution Control Board/environmental authority before the SOP is approved or revised.
Important Operational Checks for Effluent Treatment Plant Operation
The ETP operator should routinely verify the following:
- Equalization tank aeration is functioning properly.
- Effluent flow is within the approved operating range.
- Chemical dosing pumps are working correctly.
- pH is within the required operating range.
- Proper floc formation is observed.
- Tube Settler sludge is removed periodically.
- Surface Aerator is operating properly.
- MLSS is maintained within the established range.
- Sludge return from the secondary clarifier is adequate.
- Excess sludge is removed when required.
- MGF and ACF are functioning properly.
- Filter backwashing is performed as required.
- Treated water tank level is monitored.
- Flow meter readings are recorded.
- Centrifuge operation and sludge dewatering are monitored.
- Daily treated-effluent testing is completed.
- Any abnormal observation is recorded and reported.
Abbreviations
| Abbreviation | Extended Form |
| SOP | Standard Operating Procedure |
| ENG | Engineering |
| ETP | Effluent Treatment Plant |
| MLSS | Mixed Liquor Suspended Solids |
| BOD | Biochemical Oxygen Demand |
| COD | Chemical Oxygen Demand |
| TSS | Total Suspended Solids |
| TDS | Total Dissolved Solids |
| PE | Polyelectrolyte |
| TS | Tube Settler |
| AT | Aeration Tank |
| SA | Surface Aerator |
| EQ | Equalization Tank |
| SC | Secondary Clarifier |
| SV | Sludge Volume |
| MGF | Multi Grade Filter |
| ACF | Activated Carbon Filter |
| DAP | Diammonium Phosphate |
| TCCA | Trichloroisocyanuric Acid |
FAQ’s Frequently Asked Questions
What is an Effluent Treatment Plant (ETP)?
An Effluent Treatment Plant is a waste water treatment system used to collect and treat industrial effluent before the treated water is reused or discharged according to applicable environmental requirements.
What is the purpose of an Equalization Tank in an ETP?
The Equalization Tank collects incoming effluent and helps balance variations in flow, pH and pollutant concentration.
What is the role of MLSS in an ETP?
MLSS represents the concentration of suspended solids, including microorganisms, present in the mixed liquor of a biological treatment system.
Why is aeration required in an ETP?
Aeration supplies oxygen to microorganisms so that they can biologically break down biodegradable organic matter in the wastewater.