In a wastewater treatment system, it would be valuable if one could learn in advance how operational changes such as the addition of certain chemicals, nutrient, or bioaugmentation products might affect the biological wastewater treatment plant. It would also be beneficial if a plant could determine the biodegradable fractions of a stream or the optimal food to mass (F/M) ratio and sludge retention time. This knowledge would allow one to make better business and operational decisions, minimize upsets and prevent potential compliance issues.

EBS utilizes a laboratory method known as respirometry to answer these questions. Respirometry is a versatile tool that allows us to conduct studies aimed at evaluating and optimizing treatment plant performance. Respirometry testing is an ideal technique for evaluating the effects of chemical and biological additives in biological wastewater treatment systems. Other process control factors that can be measured include the kinetics of wastewater treatment, oxygen utilization rates, and the impact of toxic shock events.

What is respirometry?

Respirometry is a technology used to measure and interpret oxygen consumption in the biomass as total consumption or rate of consumption in a biological wastewater treatment plant. This oxygen consumption, or respiration, is proportional to the biodegradable fraction of the COD where the more substrate available to the bacteria, the more oxygen is consumed. In other words, oxygen uptake is proportional to bacterial activity in the sludge. Changes in oxygen uptake can occur in the presence of a toxicant or any inhibitory condition that specifically affects the biomass. Respirometry can take the form of more advanced tests utilizing computer-controlled tests spanning hours to days that are run on our  Challenge systems to simple tests run on dissolved oxygen meters.


Computer-controlled respirometers can be used for more advanced BOD testing, biodegradation assessments, bioremediation testing, and toxicity screening studies. These instruments precisely supply and measure oxygen concentrations needed to sustain biological reactions in liquids or semi-solids within reactors over extended periods of time.

Challenge Respirometer

The Challenge Respirometer System facilitates precision measurement and continuous recording of respiration rates on up to 32 reactors simultaneously for both aerobic and anaerobic lab-scale cultures. This system can be operated in the aerobic mode in which oxygen uptake is measured or in anaerobic mode in which the production of biological gasses is measured.

Challenge AER200

Dissolved Oxygen Testing via DOUR/SOUR

The Dissolved Oxygen Uptake Rate (DOUR; mg O2/L/h) test measures the respiration rate of microorganisms by calculating how quickly the biomass consume the oxygen. This test can be completed in a matter of minutes and gives us an idea about how much BOD is available for respiration.  The Specific Oxygen Uptake Rate (SOUR) is the DOUR standardized to the biomass of the solution; it is defined as the milligram of oxygen consumed per gram of volatile suspended solids (VSS) per hour (mg O2/g VSS/h). DOUR/SOUR can be used as a real-time monitoring approach to improve process operation and troubleshoot a variety of treatment issues.

DOUR/SOUR is used for:

•Daily performance monitoring

•Identifying toxicity

•Determining viability of lightly loaded systems

•Balancing loading and flows in parallel basins

•Monitoring recovery from upsets


Learn about the microorganisms in your wastewater treatment system.