Bioassays for the determination of nitrification inhibition

Sammanfattning: Requirements for nitrogen reduction in wastewater treatmentplants were introduced in Sweden in the early 1990?s. Thiswas a governmental move to reduce the nitrogen discharges tothe Baltic and Kattegatt in order to prevent eutrophication.The nitrification process in wastewater treatment plants isperformed by nitrifying bacteria. These are susceptible toinhibition and it is of great importance that the influentwater does not contain toxic compounds. Therefore, there is aneed for assays for the determination of nitrificationinhibition. This thesis describes the development andapplications of such bioassays.Pure cultures ofNitrosomonassp. andNitrobactersp. were isolated from activated sludge of awastewater treatment plant. These cultures were used as testorganisms in the development of bioassays for nitrificationinhibition measurements. The assays are based on two differentprinciples; cell suspensions of the bacteria, performed in testtubes, and mediated amperometric biosensors with the bacteriaimmobilised. Ammonia oxidation and nitrite oxidation arestudied separately without interference from other organisms,which makes it easier to interpret the results.The cell suspension assays were applied to samples ofindustrial and municipal wastewater. TheNitrosomonasandNitrobacterassays showed to have different inhibitionpatterns. A large percentage of the Swedish municipalwastewater treatment plants were found to receive inhibitoryinfluent water, but the inhibition level was generally low.Compared to an assay based on activated sludge, the screeningmethod, the pure culture assays found more samples of influentwater strongly inhibitory or stimulating. The highestcorrelation was found between the screening method and theNitrosomonasassay. TheNitrobacterassay was found to be the most sensitivemethod. Assessment of toxicity of a number of chemicalsubstances was studied using the biosensors, together with thecell suspension assays.Nitrobacterbiosensors showed to be more sensitive thantheNitrobactercell suspension assay.In addition, the pure cultures ofNitrosomonasandNitrobacterwere used for development of aquantification method for nitrifying bacteria. Applied to theflows in a wastewater treatment plant, a large amount ofnitrifiers were shown to be present in the influent water.Key words: nitrification inhibition, pure cultureassays,Nitrosomonas,Nitrobacter, mediated amperometric biosensor, wastewatertreatment, quantification.