Part 1 of 3 · Bangladesh water and wastewater careers. Search for ETP Operator, Assistant ETP Operator, WWTP/ETP Operator, WTP Operator, and Plant Operator (RO). A combined ETP/WTP job may cover two quite different systems. Read the duties and ask what you will run on shift.
A good operator answer says what you observed, what you checked first, what you were authorized to do, and what you wrote in the log. If you have worked on only one type of plant, say so and explain what you would learn from the other plant’s flow diagram and SOP.
ETP and shift operation
1. Walk me through an ETP. What does each stage do?
A typical industrial train may have screening, equalization, physical or chemical treatment, biological treatment, solids separation, and polishing where required. Follow the actual flow diagram, including return sludge and sludge handling. Explain what each step removes or controls.
2. What do you check when taking over a shift?
Read the last shift’s alarms and open actions. Walk the plant for abnormal level, leaks, noise, and standby equipment availability. Compare flow, pH, aeration-tank DO and relevant outlet readings with the site limits, then log and escalate deviations.
3. What do pH, DO, BOD, COD, and TSS tell you?
pH indicates acidity or alkalinity. DO is dissolved oxygen. BOD estimates oxygen demand from biological degradation under the test conditions; COD measures chemically oxidizable material as oxygen equivalent. TSS measures suspended solids. A clear-looking sample alone cannot establish compliance.
4. Effluent color or turbidity rises. What do you do?
Verify the reading and location. Trace the change upstream through influent, equalization, dosing and solids separation. Check recent production, pump and chemical changes. Follow the off-spec response in the SOP, notify the in-charge promptly, and record the action and follow-up reading.
5. How do you check whether a coagulant dose is appropriate?
Check influent variability, pH, actual dosing-pump output and the approved jar-test results. Compare settling or filtered quality, chemical consumption and sludge generation. Adjust only within the approved procedure and confirm the downstream result.
6. A pump or blower trips. Do you reset it?
Identify the alarm, protect people and the process, and follow the site’s restart and standby procedure. Repeated resets can conceal a fault. Escalate when required and leave electrical work, hazardous-energy isolation, or confined-space entry to authorized personnel under the site procedure.
WTP and reverse osmosis
7. What is the difference between a WTP, ETP, and RO system?
A WTP conditions source water for a defined use. An ETP treats industrial wastewater for authorized discharge or further reuse treatment. RO is a membrane separation step that can be used in either train. Name the actual feed, product requirement and disposal route for reject.
8. When should a media filter be backwashed?
Use the site criteria, which may include differential pressure, filtrate turbidity, or run time. Verify the flow path and backwash water availability, use the approved sequence, and check filtrate quality before putting the filter back into service.
9. Which readings belong in an RO log?
Record feed, permeate and reject flows, relevant pressures and pressure drops, feed and permeate conductivity, temperature, and pretreatment status. Trend them against a clean baseline. A pressure drop is meaningful only when you identify the measurement points and compare similar operating conditions.
10. Calculate recovery and apparent salt rejection.
Recovery = permeate flow ÷ feed flow × 100. At 7 m³/h permeate and 10 m³/h feed, recovery is 70%. Approximate conductivity-based rejection = (1 − permeate conductivity ÷ feed conductivity) × 100. At 20 and 1,000 µS/cm on a comparable temperature basis, it is 98%. They measure different things.
11. RO permeate flow falls or conductivity rises. What comes first?
Verify the meters and compare feed temperature, pressure, conductivity and pretreatment. Check normalized trends and stage pressure drops with the in-charge. A falling flow or rising conductivity has several possible causes. Protect product quality under the SOP and use the approved decision criteria before any cleaning or restart.
12. How do you hand over an unresolved fault?
State the time, equipment, readings, what changed, actions already taken, any isolation or off-spec water, who was informed, and the next check. If you sampled, leave the point, time and sample identifier. That is more useful than writing only ‘plant running.’
Practice before the interview
Practice drawing one plant you know and giving a one-minute shift handover. Bring a de-identified log example if you have permission to share it.
More in this series
- ETP In-Charge & ETP/WTP Manager Interview Questions
- ECR Officer & Environmental Compliance Interview Questions
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