Biodegradation tests involve testing samples in response to various parameters: dilution, nutrient addition, pH, temperature, and others. The pattern of oxygen uptake in aerobic tests; nitrogen gas production in anoxic denitrification tests; methane production in methanogenic tests; hydrogen production during glycolysis; and carbon dioxide production during fermentation reactions gives a measure of the rate and extent of biodegradation of the organic constituents of the test sample.
Pulse-Flow respirometers can be used to assess biomass activity for aerobic and anaerobic reactions. In aerobic tests, cultures are combined with nutrients, trace minerals, and an organic substrate – such as acetic acid or ethanol. The maximum oxygen uptake rate reflects the amount of active biomass in the test culture.
Toxicity of pure chemicals is assessed using respirometers by adding increasing concentrations to an active culture. The concentration at which oxygen uptake or gas production begins to decrease is known as the “threshold toxicant concentration.”
Intrinsic kinetic tests involve adding relatively high concentrations of organic substrate to small concentrations of acclimated microorganisms so that the COD/VSS ratio typically is greater than 10. Kinetic parameters are then determined by non-linear modeling using well-known relationships between biological growth and oxygen uptake.
Anaerobic biodegradation tests – often referred to as Biochemical Methane Production (BMP) tests – involve addition of known amounts of a chemical or wastewater to anaerobic cultures. The quantity of methane production – relative to that from a control – indicates the biodegradation potential. This case study shows methane production for a Control reactor and three test reactors that were operated at 20-, 30- and 45-day retention times and received three doses of industrial wastewater....
Pulse-Flow respirometers can be used to assess biomass activity for aerobic and anaerobic reactions. In aerobic tests, cultures are combined with nutrients, trace minerals, and an organic substrate – such as acetic acid or ethanol. The maximum oxygen uptake rate reflects the amount of active biomass in the test culture. Examples are shown below:
This example shows the results of dosing an anaerobic culture with three concentrations of an industrial cleaning agent followed by respirometric measurement of methane production. The threshold toxic concentration was less than 80 mg/L of product and 600 mg/L produced a 50% decrease in methane production rate.
This example shows the results of respirometer tests in which three concentrations of cyanide were added to a aerobic test culture that received phenol as an organic substrate. The threshold toxic concentration of cyanide was 1 mg/L
The pattern of oxygen uptake– relative to that for a control substrate – gives a measure of the rate and extent of biodegradation of the organic constituents of the test sample. In this case, samples #2 and #3 showed a much lower biodegradation rate than the Control.
This case study shows how respirometers can be used to measure the impact of an industrial wastewater on the nitrification reaction in a treatment plant. In this case, samples containing up to 60% wastewater by volume showed evidence of nitrification inhibition.
Anoxic denitrification requires the presence of an organic substrate to serve as an electron donor. This case study shows how respirometry was used to determine the effect of C/N ratio on denitrification rates. Such testing can be used to determine optimum internal recycle rates or supplemental carbon addition to biological denitrification plants.