Use of anaerobic respirometers for measuring gas production in toxicity and treatability tests


Anaerobic processes are used widely for stabilizing domestic sludges, treating industrial wastes, and converting biomass to methane. These processes frequently receive complex organic chemicals that are classified as being hazardous or toxic. Despite advances in our understanding of anaerobic reactions, there is limited information regarding the impact of toxic chemicals on the kinetics of anaerobic reactions. One means of determining these impacts is to measure the volume and rate of gas produced in anaerobic reactors. Laboratory tests designed for this purpose usually are based on the use of small bench-scale reactors, typically 50 to 500 mL, containing anaerobic cultures that are dosed with various amounts of test waste or chemical. The decrease in the rate or volume of gas production indicates the adverse effect of the test substance. The challenge of such tests is to measure the gas production accurately and precisely. Previous means have included use of volumetric displacement devices, wet test meters, calibrated pressure manometers, or manual removal with syringes. Either method is time-consuming or subject to numerous sources of error or both.

A new device - named the anaerobic respirometer - has been developed to help correct these deficiencies. This device measures gas production in incremental volumes as small as 0.10 mL. Tests with the device show precisions better than 3% coefficient of variability including natural biological variations. Calibration error is less than 1%. The anaerobic respirometer saves considerable test time and provides output in the form of a computer file that can be transported directly to spreadsheets or other data processing software.

The objective of this paper is to review the operating characteristics of gas flow measuring methods and to show how automatic respirometers that provide essentially instantaneous response to changes in gas flow rate allow much greater insight into the reaction of an anaerobic culture to a change in environmental or input conditions.

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