Model sewage treatment plant

Principle

Determination of biodegradability in a model sewage treatment plant via DOC/COD-measurement and substance specific analysis. Experiments with laboratory-scale sewage treatment plants are performed to simulate the complex behaviour of substances or wastewater in biological treatment plants.

Abstract

Two laboratory treatment plants are inoculated by an activated sludge taken from a municipal treatment plant, and receive synthetic wastewater in a flow-through mode. One laboratory treatment plant will receive the test substance (= test system), and one plant operates without test substance (= control system). The DOC value of the composite samples is determined daily in the effluent of both treatment plants. From the difference of the DOC obtained in the outflow, the different degradation and elimination extents are calculated in relation to the carbon content of the test substance.

The mean value of the outliner-free elimination extents within the plateau phase (for a period of at least 21 days) is defined as the test result.

Test substance properties

The method is used for substance which are soluble in water, not toxic and which have a low volatility.

The DOC value of the composite samples is determined daily in the effluent of both treatment plants. In order to obtain about the same composition of microorganisms in both systems, they are connected by daily exchanging 1.5 litre of activated sludge between both plants (=Coupled Units Test). From the difference of the DOC obtained in the outflow, the different degradation or elimination extents, respectively, are calculated in relation to the carbon content of the test substance, thereby considering the transfer of the test substance into the control systems by sludge exchange. The mean value of the outliner-free elimination extents within the plateau phase (for a period of at least 21 days) is defined as the test result. In parallel, the nitrification of the treatment systems is determined by means of nitrogen analysis, to identify any disturbances to the test performance that may be caused by the test conditions or the test substances.

The test procedure can be combined with ecotoxicity tests, to determine the aquatic toxicity of test substance residuals or of degradation products, respectively, in the effluents. As an example, this particular test is recommended for water leaching from landfills (Appendix 51 of the German Wastewater Ordinance).