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
Follow your site SOP
This is a typical operating sequence for learning. Your instrument model and approved SOP take precedence.
STAGE 1

Before you start

  1. 1Check the reactor is within its temperature check due date.
  2. 2Inspect tubes for chips or scratches; discard any damaged tube.
  3. 3Switch on and set 150 °C. Allow the block to reach set point (often 20–30 minutes).
  4. 4Homogenise samples with suspended solids in a blender so a small aliquot is representative.
  • Damaged tubes may crack under heat and acid. Always use the safety shield.
STAGE 2

Loading

  1. 1Pipette the digestion solution and the sulphuric acid–silver sulphate reagent into each tube as per the method (or use pre-filled vials).
  2. 2Add the sample carefully down the inside of the tube so it forms a layer, then cap tightly.
  3. 3Invert each tube several times to mix. The tube becomes very hot because acid is mixing with water.
  4. 4Prepare a reagent blank (purified water) and a KHP check standard with each batch.
  • Hold tubes by the cap and wear a face shield and acid-resistant gloves when mixing.
  • Never add sample to an uncapped tube and then shake.
STAGE 3

Digestion

  1. 1Place tubes in the pre-heated block and start the 2-hour timer.
  2. 2Keep the safety cover closed.
  3. 3At the end, switch off or let the timer end the program.
  • Do not open hot tubes; pressure builds up inside.
STAGE 4

Cooling and measurement

  1. 1Move tubes to a rack and let them cool to room temperature (some methods invert once while still warm).
  2. 2Wipe the outside of tubes before placing them in a spectrophotometer, or transfer contents for titration.
  3. 3Record block temperature, start and end times in the log.
In LimsPulse · Calibration Management

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

See how