CHEMICAL OXYGEN DEMAND (COD)

Chemical Oxygen Demand or COD is a measurement of the oxygen required to oxidize soluble and particulate organic matter in water. COD can be measured in rapidly or in real-time with Real Tech’s COD instruments to improve wastewater process control and plant efficiency.

HOW TO MEASURE COD IN REAL-TIME

To measure COD rapidly or in real-time, Real Tech’s innovative BOD/COD meter and BOD/COD sensors utilize patent-pending and proprietary technologies to provide superior measurement performance across multiple wavelengths of light using UV LEDs.

Many compounds absorb light in the UV-VIS spectrum including organic compounds. The instruments measure organics in a multi-dimensional way that results in improved correlations to aggregate organics water quality parameters, such as BOD and COD. This also allows the sensors to be able to detect changes in the composition of organics independently of their concentration.

To ensure the results are as accurate and predictive of the lab as possible, Real Tech’s Liquid Ai^® platform suite of services can be used in combination with our BOD/COD instruments

For rapid testing with our BOD/COD meter, the Liquid Ai^® Data Management PC software empowers users to create their own custom calibrations to capture site-specific water conditions in addition to various other sample and calibration management abilities.

For continuous, real-time monitoring with our BOD/COD sensors, the Liquid Ai^® data analytics services provide ongoing calibration health monitoring. The service enables continuous calibration improvements to be made as water quality composition changes or new contaminants are introduced. We ensure reliability and trust in the results, so our clients can make confident, informed decisions to improve their plants processes. The longer our systems are installed, the smarter and more insightful they become with our Liquid Ai^® services.

IMPORTANCE OF COD FOR WASTEWATER

Chemical Oxygen Demand is an important water quality parameter because, similar to BOD, it provides an index to assess the effect discharged wastewater will have on the receiving environment.

Higher COD levels mean a greater amount of oxidizable organic material in the sample, which will reduce dissolved oxygen (DO) levels. A reduction in DO can lead to anaerobic conditions, which is deleterious to higher aquatic life forms.

The COD test is often used as an alternate to BOD due to shorter length of testing time.

BENEFICIAL APPLICATIONS FOR COD MONITORING

Real-time or rapid COD monitoring is becoming increasingly popular, and it’s no surprise as the alternative is a 2-5 hour wait for lab results.

Continuous organics monitoring opens the door for many new treatment process control and optimization possibilities that can result in significant cost savings, improved water quality, and compliance peace of mind.

Wastewater applications for online COD measurement include:

LABORATORY DELAY FOR COD RESULTS LIMITS ACTION

A common method for Chemical Oxygen Demand analysis involves using a strong oxidizing chemical, potassium dichromate Cr₂O₇^2-, to oxidize the organic matter in solution to carbon dioxide and water under acidic conditions.

Often, the test also involves a silver compound to encourage oxidation of certain organic compounds and mercury to reduce the interference from oxidation of chloride ions.

The sample is then digested for approximately 2 hours at 150°C. The amount of oxygen required is calculated from the quantity of chemical oxidant consumed.

Relying on grab samples leads to significant delays. When results come back from the lab, the information is usually of little value for process control and improving plant performance.

Plants need a practical solution that delivers continuous information on wastewater composition and quality to operations personnel. Real Tech has the solutions to help our clients get the information they need, when they need it.