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Wastewater Management – Chemical Oxygen Demand (COD) Testing

Written by Janice M on . Posted in Water & Environmental

What is COD?

The COD Test is commonly used to indirectly measure the amount of organic compounds in water. Most of the waste in effluent / waste water comes from organic compounds, primarily lost product. As these substances oxidise or stabilise, they combine with some of the oxygen dissolved in the water. Atmospheric oxygen can replenish the dissolved oxygen supply, but only at a slow rate. If there is not enough dissolved oxygen in the water, the aquatic life can die. Under extreme conditions, the water may turn black and produce a foul odour.

The amount of oxygen used is therefore a good indicator of the amount of organic waste present. It is expressed in mg / litre, which indicates the amount of oxygen consumed per litre of solution.

Why Measure COD?

This is a very good indicator of water quality and a check commonly used by Municipalities and governing bodies to assess water quality. The requirements for effluent / waste water to be discharged to other areas by DWA (Department of Water Affairs) in South Africa are as follows:

SUBSTANCE / PARAMETER SPECIAL LIMIT ~ WATER TO RIVERS ~  MAXIMUM CONCENTRATION GENERAL LIMIT ~WATER TO OTHER AREAS ~ MAXIMUM CONCENTRATION
Chemical Oxygen Demand (COD) less than 30 mg/l after corrective Chlorine less than 75 mg/l after corrective Chlorine

* DWA – Requirements for the Purification of waste water or effluent, Act No. 991 – 18 May 1984

Industries are required to monitor the organic loading (wastes produced in food, beverage and various other industry’s processing operations) of their waste / effluent water. Companies that do not comply with the regulations can harm the environment and receive fines, surcharges, or civil and criminal penalties.

Routine COD testing will enable companies to determine their compliance and where their greatest waste originates. The COD test takes up to 2 hours to show results can also be a tool for measuring lost product and wasteful practices.

Greater numbers of manufacturers are taking steps to reduce waste water and save water because of rising treatment costs and increased environmental standards.

cod_setup lgLOVIBOND® VARIO REQUIREMENTS FOR MEASURING COD

  1. Add sample to a Lovibond® COD Vario test tube.
  2. Heat it in the Reactor to allow sample digestion.
  3. Analyse in a handheld Lovibond® MD photometer; or using a benchtop Lovibond® MultiDirect or SpectroDirect.

Requirements: COD tube tests, available in 3 ranges: low, middle, high; test tube stand; Reactor; Lovibond® photometer.

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Historical comments (9)

    • Janice

      |

      The limit of sewage water is usually 100 mg/l.

    • Janice

      |

      You are testing how much Oxygen is in the water to support life. This also equates to the level of pollution in the water. Is the water safe or should you take corrective measures to purify the water? Please let me know if you need any further information.

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