Inhibition Tests

Our inhibition toxicity tests measure the impact of trade waste on the rate of oxygen uptake by biomass from a WwTP. The result is provided as a percentage inhibition. e.g. if a wastewater completely inhibits oxygen uptake, the test result would be 100% inhibition. If the wastewater has no toxic effect on oxygen uptake, the test result would be 0% inhibition. The test differentiates between inhibition of the total biomass, and inhibition of the nitrifying component of the biomass.

If you have several trade waste discharges, we can run a screening test to determine the relative impact of the different trade wastes on wastewater biomass. This will determine whether one or more of the trade waste discharges are likely to significantly impact on the performance of your WwTP. In this way, we can rapidly screen the toxicity of up to five different trade waste samples in a single test run.

If a screening test identifies a trade waste which may have a significant impact on the performance of your WwTP, or if you have a particular trade waste discharge you suspect may impact the biological treatment processes, we can run a more detailed inhibition test on a range of dilutions to determine the EC10, EC20 and EC50. These are the concentrations of the trade waste that cause 10%, 20% and 50% inhibition of total biomass activity and nitrification respectively.

To test for inhibition, we run two sets of tests. The first is a standard respirometry test to determine the total oxygen uptake by the biomass, and the inhibition of the trade wastes on this respiration. In the second test we add a nitrification inhibitor, usually Allylthiourea (ATU), to the biomass. Oxygen uptake measured during this second test represents oxygen used by non-nitrifying bacteria. By subtracting the results of the second test from the results of the first, oxygen uptake due to nitrification, and inhibition of nitrification, is determined.