Skip to content

Plant problem

Treated water is not meeting the required standard

The plant is running, but the outlet will not hold the parameter you are measured against — either consistently, or at the moments that matter.

Typically arises in

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

Symptoms, not causes

You may also be seeing

  • One parameter (BOD, COD, TDS or another) fails while the others stay inside limit
  • The outlet holds at low load and fails when production is full
  • Failures cluster on particular shifts, days or seasons
  • Plant results and external laboratory results do not agree
  • Performance has drifted downwards slowly, with no single event to point at

What helps, if you have it

  • Outlet test results over recent months
  • Design basis or original process drawings, if they still exist
  • Daily operating log, dosing records and flow records

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

What is actually arriving

  • Real influent load and characteristics against the design basis
  • Shock loads, batch discharges and streams that were never in the original scope
  • Inhibitory or toxic constituents reaching a biological stage

Line of enquiry02

The biological stage

  • MLSS, F/M ratio and sludge age against what the process needs
  • Dissolved oxygen through the tank, not at one probe
  • Settleability, sludge structure and return sludge rate
  • Nutrient balance where the effluent is nutrient-deficient

Line of enquiry03

Hydraulics and retention

  • Actual retention time against design retention time
  • Short-circuiting, dead zones and uneven distribution
  • Weir levels, sludge blanket depth and clarifier surface loading

Line of enquiry04

Chemical and tertiary stages

  • Dosing point, sequence, mixing energy and pH window
  • Filtration media condition and backwash regime
  • Disinfection contact time and demand

Line of enquiry05

Measurement itself

  • Where and how samples are drawn, preserved and tested
  • Whether the reported failure is a treatment failure or a sampling artefact
How an investigation runs, step by step

Talk to an Expert

Show us this on your plant.

This problem is carried across to the form as your starting point. You can change it there.

Talk to an Expert

A specialist calls you and tells you the right next step and its cost.

Not quite it?

Last updated