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Plant problem

Chemical consumption is too high

Chemical cost is usually a utilisation problem before it is a price problem. The same reagent, dosed differently, frequently does more.

Typically arises in

  • ETP
  • WTP
  • 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

  • Chemical or polymer dosing has risen with no change in influent load
  • Consumption is set to a worst case and never reduced
  • Sludge volume has increased in step with dosing
  • pH control hunts, overshoots, or is corrected by a second chemical
  • Different operators dose differently, and both appear to work

What helps, if you have it

  • Chemical consumption records against flow and load
  • Dosing set-points as actually operated, including manual overrides
  • Any jar-test data, however old

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

How the chemical is delivered

  • Dosing point, and whether the reagent reaches the reaction it is meant for
  • Mixing energy and mixing time — rapid mix and flocculation are separate duties
  • Dosing sequence where more than one reagent is in use

Line of enquiry02

Whether the dose is the right dose

  • Jar-test basis, and whether current practice still reflects it
  • Reagent strength, dilution and age
  • pH window at the point of reaction, not at the outlet

Line of enquiry03

Control

  • Instrument calibration and control loop behaviour
  • Manual dosing set for the worst hour and left there
  • Flow-proportional dosing where flow itself is not measured

Line of enquiry04

What the dosing is compensating for

  • An upstream stage not doing its work, corrected downstream by chemistry
  • Two reagents working against each other
How an investigation runs, step by step

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