ETP discharge monitoring — what to measure and record

Short answer: Discharge compliance usually requires continuous monitoring with records, not occasional sampling. The parameters typically monitored online are pH, flow and turbidity or TSS, with COD and BOD by laboratory analysis.

Requirements vary by state pollution board, industry and discharge point, so confirm your specific consent conditions rather than assuming.

Why continuous monitoring

Occasional sampling only tells you about that moment. Continuous monitoring:

• Provides the record that compliance requires
• Alerts you before a limit is breached, so you can act
• Shows the plant is working, which matters during inspection
• Helps diagnose problems, since you can see when things changed

What is typically monitored online

Why an electromagnetic flow meter for discharge

Effluent contains solids and is often corrosive, which rules out mechanical meters with moving parts. An electromagnetic meter has no obstruction in the flow path, so:

• Nothing to block or wear
• Solids pass through without affecting the reading
• It gives a 4-20mA or RS485 output for recording
• Accuracy is maintained over time

See our electromagnetic flow meter guide.

Telemetry

Many pollution boards now require data to be transmitted directly to their server. A telemetry modem (₹13,650) takes the 4-20mA or RS485 outputs from your instruments and transmits them.

What this means practically: your readings are visible to the board continuously, so instrument reliability and calibration become important. An uncalibrated sensor transmitting wrong data is worse than no data.

Data logging

Even where telemetry is not required, a datalogger (₹18,900) keeps a local record. This is useful for:

• Demonstrating compliance during inspection
• Investigating what happened when something went wrong
• Showing trends over months

Laboratory parameters

Some parameters cannot be measured online and require laboratory analysis:

Keep the laboratory reports filed with your online records — together they form the compliance file.

Sensor calibration matters here

Calibrate monthly and record each calibration — the record itself is part of demonstrating good practice. See our calibration guide.

ETP grade sensors

Standard sensors do not survive in effluent. A standard pH sensor typically lasts two to four months in an ETP, while an ETP grade sensor lasts twelve to eighteen.

Where compliance depends on the reading, sensor reliability is not the place to economise. See our ETP sensor guide.

Keeping the record

A compliance file should contain:

1. Continuous instrument records (logger or telemetry)
2. Laboratory analysis reports
3. Calibration records for each instrument
4. Maintenance log for the plant
5. Chemical consumption records
6. Any incident reports and what was done

The maintenance and calibration records matter more than people expect — they demonstrate the monitoring itself is trustworthy.

Keeping a spare sensor

If the pH sensor fails, you have no compliance record until it is replaced, and a new sensor can take several days to arrive. On a plant where discharge is monitored, keeping a spare is a straightforward precaution.

What to check with your pollution board

• Which parameters must be monitored online
• Whether telemetry is required
• The specific limits for your industry and discharge point
• Required record retention period
• Laboratory analysis frequency

These vary considerably, so confirm your own consent conditions rather than relying on general guidance.

Frequently asked questions