LimsPulse
Environmental monitoring

COD Digestion Reactor

A dry heating block that holds sealed glass tubes at 150 °C for two hours so that potassium dichromate can oxidise the organic matter in water and wastewater samples. It is the heart of the closed reflux COD test.

  • Environmental testing laboratories
  • Municipal water and wastewater utilities
  • Chemical and pharmaceutical effluent treatment
  • Food and beverage processing
  • Textile, pulp and paper, and distilleries
Illustration of COD Digestion Reactor
TROUBLESHOOTING

Common problems, causes and fixes

KHP standard recovers low
Likely causes
  • • Block temperature below 150 °C
  • • Digestion time too short
  • • Old or wrongly prepared digestion reagent
What to do
  • • Check block temperature with a calibrated thermometer
  • • Confirm the timer runs a full 2 hours
  • • Prepare fresh reagents or use a new vial lot
Results erratic between replicate tubes
Likely causes
  • • Sample not homogenised
  • • Poor mixing of tube contents before digestion
  • • Uneven temperature between wells
What to do
  • • Blend samples with solids before sub-sampling
  • • Invert tubes thoroughly after capping
  • • Run a well-to-well temperature uniformity check
Tube cracks or leaks during digestion
Likely causes
  • • Scratched or reused damaged tube
  • • Cap not tight or liner damaged
What to do
  • • Discard damaged tubes
  • • Replace caps or liners; tighten firmly
Positive bias in saline effluents
Likely causes
  • • Chloride not fully masked
What to do
  • • Check mercuric sulphate dose against chloride content
  • • Dilute the sample or use a high-chloride method
Block will not reach set point
Likely causes
  • • Heater or sensor fault
  • • Controller set wrongly
What to do
  • • Check set point and program
  • • Call service to check heater and sensor
In LimsPulse · Calibration Management

Keep every COD digester in control: usage logs, calibration and maintenance schedules, and automatic blocking of overdue instruments.

See how