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.

Simulated workplaceIntermediate missionCAQA ClearFlow Water

What is going on

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.

Greg Tan, Wastewater Treatment Manager
Subject: Low dissolved oxygen in reactor 2 and a low pH slug at the inlet

Reactor 2 dissolved oxygen dropped to 0.6 milligrams per litre overnight and the ammonia in the clarifier effluent is creeping up. On top of that the inlet works picked up a low pH slug this morning, which we think came from the Merriwa food plant. I need you to assess the activated sludge process this shift: review the aeration, sludge age, mixed liquor and settleability data, sample the reactor and clarifier, work out what to adjust and by how much, and make sure the effluent licence samples are taken. Log the samples in the Water Quality Sampling Register and write a shift summary for me.

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.

Work through it

You do not need to do it all. Doing a few of these will show you what the work is like. Your ticks and notes stay on this device.

Read the Environmental Management Policy section on licence compliance and list the effluent parameters and limits you must protect today.
Review the reactor 2 data for dissolved oxygen, mixed liquor suspended solids, sludge age, wasting rate, blower output and inlet flow and pH over the last seven days and summarise the trends.
Sample reactor 2 mixed liquor and clarifier 2 effluent, run settleability and a microscopic check for filaments, and record the results in the Water Quality Sampling Register.
Assess the causes of the low dissolved oxygen, including sludge inventory, blower capacity and the low pH slug, and explain how each affects nitrification.
Decide the adjustments to wasting rate, blower setpoints or flow split between reactors that are within an operator's authority, apply them and record the time and reason for each.
Collect the effluent licence samples at the licence point with chain of custody, enter them in the register and confirm the report deadline in the calendar.
Notify the Customer and Trade Waste Manager of the pH slug evidence in writing so it can be investigated under the Trade Waste Policy, and record the notification.
Write a shift summary for the Wastewater Treatment Manager with the data, the adjustments, the expected response time and what needs a manager's decision, such as the blower repair.

My notes: what did I enjoy, and what surprised me?

What someone in this role would produce

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

Printing this is a record of what you explored. It is not a certificate or a qualification.