Recent advancements in pressure sensor technology have allowed for a new, simplified method for BOD measurement.
Biochemical Oxygen Demand (BOD) is the measurement of the amount of oxygen consumed by the decomposition of organic matter in a biochemical process over a defined period of time. It is an important analytical tool in determining the effects of effluents on water treatment plants and surface water systems. The most common method for measuring BOD is the dilution method. However, this method takes a considerable amount of time and preparation to complete.
The new Oxi700TM BOD System by Orbeco-Hellige Inc. is a manometric respirometer that directly measures the oxygen consumed by microorganisms in wastewater. The instrument measures the pressure changes that occur as microbes consume the organic matter in the sample.
The process is simple: the water sample is placed directly into a sample bottle which is then sealed and kept at a constant temperature (20°C). During the measurement cycle, the microorganisms consume oxygen in the sample. The reduction in oxygen in the water creates a concentration gradient which causes oxygen in the headspace to dissolve into the water sample. Carbon dioxide, which is released by the microorganisms during the decomposition of the organic matter, can interfere with oxygen measurement and is therefore eliminated by reacting with potassium hydroxide. The resultant decrease in pressure (from the consumption of oxygen and the elimination of carbon dioxide) corresponds to the oxygen uptake of the microorganisms and is measured by the instrument and then displayed as a BOD value.
One advantage of manometric respirometers is that no sample dilutions or seeding of the sample are required. A common source of error with the dilution method comes from the preparation of sample dilutions and from seeding the sample with microorganisms. Since dilutions and seeding are not required, the total set up time for the measurement also is reduced.
Another source of error occurs during the daily dissolved oxygen measurements that are required in the dilution method. The Oxi700 BOD System automatically takes BOD readings at regular intervals over the 5-day measurement period without any operator intervention. Since the respirometer displays results directly in mg/L BOD, no calculations or conversion charts are needed.
The Respirometric BOD method is approved by Standard Methods for the Examination of Water and Wastewater (Method 5210 D). It is an easy-to-use tool for process control monitoring and other non-USEPA reporting purposes. For more information on the Orbeco-Hellige system, visit www.orbeco.com.
