Most ETP failures are not sudden. They build up over two or three shifts — a DO reading that drifts low, a sludge blanket that climbs unnoticed, a chemical dosing pump that loses prime. A disciplined shift checklist catches these signals before they become consent violations.
This checklist is written for operators running ETPs in Indian industries — food processing, textiles, pharmaceuticals, chemicals. Adapt the parameters to your consent conditions, but the sequence and observation points apply broadly.
Morning Startup Checks
The first 30 minutes of a shift set the tone. Walk the plant before you touch any control panel.
| Check Item | What to Look For | Action if Abnormal | Done ✓ |
|---|---|---|---|
| Inlet screen / bar screen | Blockage, rags, overflow around screen | Clear manually; log if recurring | ☐ |
| Inlet flow meter | Totalized daily flow vs. design flow | Flag if >120% design; alert supervisor | ☐ |
| Inlet pH (online or grab) | Target 6.5–8.5 for biological systems | Adjust pH correction dosing immediately | ☐ |
| Equalization tank level | Within operating range; no overflow | Adjust feed pump speed or bypass | ☐ |
| All blowers / aerators running | Amp draw normal; no vibration or heat | Switch to standby; log fault | ☐ |
| DO instrument zero check | Check in air — reading should be ~9 mg/L at 25°C | Clean probe membrane; recalibrate | ☐ |
| pH meter calibration | Two-point calibration with pH 4 and 7 buffers | Replace electrode if drift >0.3 pH units | ☐ |
| Chemical storage levels | Coagulant, acid/alkali, anti-foam, chlorine | Raise purchase order if <3 days stock | ☐ |
| Visual odour assessment | Earthy/musty = normal; sulphur = septic inlet | Log and escalate H2S immediately | ☐ |
Biological Stage Parameters
The aeration tank is the heart of any ETP. These readings tell you whether your biomass is healthy, overloaded, or starving — and give you 24–48 hours of lead time before problems reach the effluent.
Dissolved Oxygen (DO)
Measure at the mid-tank position, away from diffusers. Target: 2–3 mg/L. Below 1.5 mg/L, aerobic bacteria are stressed and filamentous organisms begin to dominate. Above 4 mg/L, you are wasting power — reduce blower output or open bypass valve.
Record DO at the start and end of each shift. If DO is falling shift-on-shift despite constant blower output, organic load has increased — check inlet COD if possible, or reduce feed flow until DO recovers.
Mixed Liquor Suspended Solids (MLSS) and MLVSS
Run the MLSS test once per shift on day shift; at minimum daily. Normal operating range for activated sludge: 2,500–4,000 mg/L. MBBR hybrid systems may run lower (1,500–2,500 mg/L) because the biofilm carriers carry additional biomass.
MLVSS (volatile suspended solids — the living fraction) should be tested twice per week. A healthy system has MLVSS/MLSS > 0.75. Falling MLVSS/MLSS ratio signals accumulation of inert solids — check for inorganic inlet loads (sand, grit, high TDS).
Sludge Volume Index (SVI) and 30-Minute Settleability
Fill a 1-litre Imhoff cone or measuring cylinder from the aeration tank mixed liquor. Read the settled volume after exactly 30 minutes (SV30). Calculate:
SVI = (SV30 in mL/L) ÷ (MLSS in g/L)
| SVI Range (mL/g) | Interpretation | Action |
|---|---|---|
| <80 | Excellent settling | No action needed |
| 80–150 | Good settling — normal range | Maintain current WAS rate |
| 150–250 | Marginal — watch clarifier | Increase WAS; check DO and nutrients |
| >250 | Bulking — clarifier at risk | Escalate immediately; selective wasting |
pH and Temperature
Biological treatment operates best at pH 6.8–7.8 and temperature 20–38°C. Record aeration tank pH every shift. In summer months when tank temperature exceeds 38°C, biological activity becomes erratic — consider insulating exposed tank walls or increasing RAS flow to introduce cooler settled sludge.
Chemical Dosing Verification
Chemical dosing failures are silent — the pump runs, but the dose is wrong. These checks confirm actual dose delivery, not just pump operation.
| Chemical | Verification Method | Target / Accept Range | Done ✓ |
|---|---|---|---|
| Coagulant (alum / PAC / ferric) | Check daily tank draw-down vs. expected dose | As per jar test — typically 50–200 mg/L | ☐ |
| pH correction (acid / alkali) | Measure pH before and after dosing point | Inlet adjusted to 6.5–8.0 | ☐ |
| Anti-foam | Visual check — foam thickness in aeration tank | <2 cm surface foam acceptable | ☐ |
| Nutrients (urea / DAP) | Check dose rate in log; confirm pump stroke | BOD:N:P ratio ~100:5:1 | ☐ |
| Chlorine (if used for disinfection) | Residual chlorine test in contact tank outlet | 0.5–1.0 mg/L residual | ☐ |
| Polymer (if belt press / centrifuge used) | Check dilution water flow and polymer concentration | Per vendor recommendation; check cake dryness | ☐ |
Tip: Mark the level on each chemical tank with a permanent marker at shift start. At shift end, measure actual drawdown and compare with the expected dose. A discrepancy of more than 20% means a pump fault, line blockage, or dilution error — find it before it shows up in your effluent results.
Daily Sludge Management
Sludge management is the most neglected part of ETP operation — and the most common cause of clarifier upset. Maintaining the right sludge age requires consistent daily wasting.
Waste Activated Sludge (WAS) Rate
Calculate target WAS volume each day based on MLSS measurement:
- Target MLSS: 3,000 mg/L
- Current MLSS: from morning test
- If MLSS is above target: increase WAS rate for the shift. Rough rule — waste 5–10% of the aeration tank volume per day to maintain sludge age of 8–15 days for a standard system.
- Never skip WAS for more than 2 consecutive days — MLSS will climb above 5,000 mg/L and the clarifier will fail.
Sludge Thickening and Dewatering
| Step | Daily Check | Done ✓ |
|---|---|---|
| WAS pump operation | Record actual WAS volume pumped (m³); compare with target | ☐ |
| Sludge thickener (if applicable) | Thickened sludge concentration (>2% TS preferred) | ☐ |
| Filter press / belt press / centrifuge | Cake dryness (target >20% TS); cycle time | ☐ |
| Filtrate / centrate quality | Visual clarity — cloudy filtrate means polymer under-dose | ☐ |
| Dewatered cake disposal | Log quantity (MT or bags), vehicle number, disposal site | ☐ |
Dewatered sludge from ETPs treating industrial effluent is typically a Scheduled Waste under the Hazardous Waste Management Rules. Ensure disposal is only to an authorized facility and the transport document (Form 10) is retained on site for SPCB inspection.
Compliance Log Entries
The shift log is a legal document. These entries need to be complete, accurate, and signed — they form the basis of monthly SPCB Form submissions.
| Log Entry | Frequency | Required for |
|---|---|---|
| Inlet flow (m³) | Each shift (cumulative) | SPCB monthly return, CPCB OCEMS if applicable |
| Outlet flow (m³) | Each shift (cumulative) | SPCB monthly return |
| Inlet pH | Each shift | Process log; monthly report |
| Outlet pH | Each shift | Consent compliance; SPCB inspection |
| DO in aeration tank | Each shift | Process log; troubleshooting reference |
| MLSS | Daily (day shift) | WAS rate calculation; monthly report |
| WAS volume pumped (m³) | Daily | Sludge balance; monthly report |
| Chemical consumption (kg or L) | Daily | Chemical register; SPCB inspection |
| Lab results (BOD, COD, TSS, etc.) | Per consent frequency (weekly/fortnightly) | SPCB Form submission; consent compliance |
| Sludge disposal quantity and destination | Every disposal event | Hazardous waste register; SPCB Form 4 |
| Equipment faults and downtime | As they occur | Maintenance record; bypass event reporting |
If your plant has an online continuous emission / effluent monitoring system (OCEMS) with SPCB data transfer, ensure the data logger is online and the connectivity light is green every shift. A gap in OCEMS data is treated by some SPCBs as an unauthorised bypass.
Warning Signs That Predict Failures
These are the most common early-warning signals seen in Indian ETPs. Every operator should know what each symptom means and what to do in the next 30 minutes.
| Symptom You See | Likely Problem | Immediate Action |
|---|---|---|
| White or grey foaming in aeration tank | Surfactant shock (detergent-containing effluent), or nutrient deficiency causing filamentous growth | Dose anti-foam; check inlet for soap/detergent surge; verify N and P dosing |
| Thick brown or chocolate-coloured froth | Nocardia/Microthrix filamentous bacteria; often linked to nitrification in high-SRT systems | Increase WAS to reduce sludge age; add chlorine to return sludge at low dose (2–5 mg/L Cl₂) for 3–5 days |
| Pin-floc: effluent turbid with tiny particles, SV30 very low | Sludge age too low (young biomass); dispersed growth; over-wasting | Stop or sharply reduce WAS for 3–5 days; maintain DO 2.5–3 mg/L; add RAS |
| Sludge rising in clarifier, floating clumps on surface | Denitrification in clarifier causing nitrogen gas bubble lift; sludge blanket too deep; SVI rising | Increase RAS; reduce HRT in clarifier if possible; increase WAS to lower sludge blanket depth |
| H2S odour at inlet, pump sump, or equalization tank | Septic wastewater arriving — anaerobic conditions in collection network or long retention in equalization | Increase equalization mixing; dose hydrogen peroxide or nitrate at inlet; evacuate nearby personnel; check confined space entry protocol |
| DO dropping despite blowers running at full load | Organic load surge; diffuser fouling; MLSS too high consuming O₂ faster | Reduce feed flow by 20–30%; increase WAS; check diffuser backpressure for fouling |
| Effluent colour change (dark brown, grey, reddish) | Dye, chromium, or other industrial chemical discharge from process — not biological | Do not discharge. Hold in equalization; alert supervisor; collect inlet sample for analysis; notify process plant |
| High outlet TSS but normal MLSS and SVI | Short-circuiting in clarifier; surface weir uneven; scum baffle damaged | Check weir levels; inspect baffles; reduce feed rate; increase RAS |
The golden rule: when you see something unusual, log it with the exact time and take a photograph on the plant camera if available. Early documentation helps engineers diagnose intermittent problems that do not repeat during site visits.
If you are unsure whether a situation needs escalation, err on the side of calling your supervisor. A 15-minute conversation is far cheaper than a consent violation or compensation to the downstream CETP.
Need operator training or a structured ETP monitoring programme?
Spans Envirotech provides on-site operator training, shift log templates, and monthly performance review support for ETPs across India. Write to us at bd@spans.co.in or use the contact form to describe your plant and requirements.
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