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Scenario · Wastewater Treatment

Assess and adjust the activated sludge process after a low dissolved oxygen event

You are a wastewater treatment operator on day shift at the Mooroopna plant.

Intermediate3 to 5 hours8 tasks
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The situation

What has happened

Reactor 2 dissolved oxygen fell to 0.6 milligrams per litre overnight and ammonia in the clarifier 2 effluent has risen from 0.8 to 2.4 milligrams per litre over two days. The inlet works recorded a 40-minute low pH slug of 4.8 this morning, suspected to be from the Merriwa Holdings food plant. Mixed liquor suspended solids in reactor 2 is 4,200 milligrams per litre and the sludge volume index has climbed to 160. One of the two blowers on reactor 2 has been running at reduced output since a bearing fault. The monthly effluent licence samples are due today. The Wastewater Treatment Manager wants a process assessment, adjustments and a shift summary.

Your brief. Assess the activated sludge process in reactor 2 using plant data and your own samples, identify why dissolved oxygen and nitrification have fallen, make and justify process adjustments within your authority, collect and log the effluent licence samples, and report to the Wastewater Treatment Manager.
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Tasks

Deliverables

  • Seven-day process data summary
  • Water Quality Sampling Register entries for the operational and licence samples
  • Adjustment log with reasons
  • Notification to the trade waste team
  • Shift summary to the Wastewater Treatment Manager

Documents to use

Systems to use

Water Quality Sampling Register

Records operational and verification samples, laboratory results and the result status for drinking water, recycled water, effluent and raw water.

WHS and Environmental Incident Register

Records injuries, near misses, hazards, chemical releases, sewage spills, water quality incidents and vehicle events with investigation and actions.

Trade Waste Approvals Register

Holds every commercial and industrial trade waste application and approval with its category, conditions, inspections, sampling and compliance status.

For trainers and assessors

Units of competency

Current on training.gov.au for the National Water Training Package as at 10 September 2026.

NWPTRT036Operate and control activated sludge processes
NWPTRT037Operate and control nutrient removal processes
NWPTRT027Monitor and operate wastewater treatment processes
NWPGEN022Perform laboratory testing
NWPGEN018Follow environmental and licensing procedures

Qualifications

NWP30222Certificate III in Water Industry Operations
NWP40120Certificate IV in Water Industry Operations
Assessor notes

What to look for

Evidence guide

The student must link low dissolved oxygen, sludge inventory, blower capacity and the pH slug to the loss of nitrification with reasoning, not just restate the readings. Adjustments must be within operator authority and recorded with reasons. Licence samples must be taken with chain of custody and logged. Look for the trade waste notification being made in writing and the manager decisions being flagged rather than assumed.

The student's evidence summary lists every record they created or changed in the systems named above, their notes and the tasks they ticked. Verify it against the deliverables and your own assessment tool.