Chemical Oxygen Demand (COD) Testing, Instruments and More

Why Measure Chemical Oxygen Demand (COD)?

When treated wastewater is discharged into the environment, it can introduce pollution in the form of organic content to receiving waters. High levels of wastewater COD indicate concentrations of organics that can deplete dissolved oxygen in the water, leading to negative environmental and regulatory consequences. To help determine the impact and ultimately limit the amount of organic pollution in water, oxygen demand is an essential measurement.

At Hach^®, find the testing equipment, resources, training and software for COD measurement and management during water treatment.

Featured COD Product Categories

Online COD Analyzers

COD Meter

Complete online solutions for your water analysis needs.

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Benchtop COD Instruments

DR8200

Benchtop instruments can provide fast, accurate COD measurements when quick results are needed.

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Portable COD Instruments

Dr1900

Easy to use, field testing equipment for your COD needs.

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Water COD Reagents and Consumables

TNT

Hach’s quality test kits, reagents and chemistries are quick, accurate and easy to use.

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Which Processes Require Chemical Oxygen Demand Monitoring?

Influent waters entering wastewater plants are high in organics and the wastewater plant must reduce the “organic loading” before discharging water to a receiving body.

Knowledge of oxygen demand is useful throughout the treatment for measuring waste loading, evaluating the efficiency of the process and ensuring compliance with regulations for the oxygen demand of effluent.

Primary Treatment:
Clarifiers, or sedimentation basins, slow the flow of the wastewater to allow suspended solids to settle. Surface skimmers collect any floating fats, oils and greases. With the use of this mechanical and physical means, approximately 30% of organic matter is removed from the wastewater and is routed to the solids management area of the plant.
Secondary Treatment:
This process uses living organisms to aid in reducing organics. In the aeration basin, bacteria and microorganisms convert biodegradable organic matter to carbon dioxide and water. With this conversion, organics are reduced, thereby reducing oxygen demand.
Discharge Limits:
Discharge limits vary from plant to plant depending on the characteristics of the receiving water, effects on aquatic life, recreational uses and other factors. Discharge permits may stipulate a specific maximum concentration for BOD or COD, or a percent removal. Some plants require achieving as much as 90% removal of oxygen demand.

For compliance, it’s necessary to measure BOD or COD in the influent water as it enters the plant, before mechanical screening processes and at the end of the treatment at the discharge point.

When selecting a method for analyzing oxygen demand, it’s important to consider the following:

Specific testing application
Oxidant that will be used
Completion time
Accuracy and precision of the measurement

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This sedimentation basin slows the flow of wastewater to allow suspended solids to settle.

How is Chemical Oxygen Demand Monitored?

Laboratory Testing

US EPA Method 8000 TNTplus ^® Vials

Online Process Testing

EZ Series COD Analyzers

COD Testing Advantages

COD is most suitable for rapid and frequent monitoring of treatment plant efficiency and water quality.
This method is more accurate than BOD (with a 5-10% relative standard deviation) and it offers a relatively short analysis time (2-hour digestion time), compared to the 5-day BOD test.
The COD oxidant is not affected by toxic materials in the sample.
Changes in the COD value between influent and effluent may parallel BOD content and supplement BOD results.