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Plant problem

Power consumption is too high

On most treatment plants aeration is the largest single electrical load. It is also the one most often run at a fixed output regardless of demand.

Typically arises in

  • STP
  • ETP
  • RO
  • ZLD
Observation record
Reported
in the words of the person at the plant
5 signs
that often come with it
4 lines
of enquiry to check on site
Cause
not assumed from the symptom

Symptoms, not causes

You may also be seeing

  • Energy cost has risen without a change in treated volume
  • Blowers or aerators run continuously at full output
  • Power draw is unchanged when the plant is at part load
  • Equipment runs because switching it off has never been trialled
  • Motors run hot, or draw more than nameplate

What helps, if you have it

  • Electricity bills or sub-meter readings over several months
  • Blower, aerator and pump nameplate data
  • Dissolved oxygen readings, or the fact that none are taken

None of it is required to start.

What an investigation looks at.

Lines of enquiry, not conclusions. Which of them matters is decided at the plant, by evidence.

Line of enquiry01

Aeration

  • Actual dissolved oxygen against the set point the process requires
  • Fixed-speed operation where demand varies through the day
  • Diffuser fouling and the pressure penalty it creates
  • Blower sizing against real oxygen demand rather than design-day demand

Line of enquiry02

Pumping

  • Operating point against the pump's best efficiency point
  • Throttled valves and unnecessary recirculation
  • Oversized duty pumps running against a low head

Line of enquiry03

What is running and why

  • Equipment left in service that the process no longer needs
  • Sludge recirculation rates set once and never reviewed
  • Treatment stages operating when there is nothing to treat

Line of enquiry04

Electrical

  • Power factor and its effect on the billed figure
  • Where consumption is measured, and whether the plant is sub-metered at all
How an investigation runs, step by step

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