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).

Aerobic and anaerobic transformation in soil
OECD 307, Regulation (EC) No 440/2008, C.23

Soil samples are treated with the test substance and incubated in the dark in biometer-type flasks or in flow-through systems under controlled laboratory conditions. After appropriate time intervals, soil samples are extracted and analysed for the parent substance and for transformation products. Volatile products are also collected for analysis using appropriate absorption devices. Using ¹⁴C-labelled material, the various mineralisation rates of the test substance can be measured by trapping evolved ¹⁴CO₂ and a mass balance, including the formation of soil bound residues, can be established.

Aerobic and anaerobe transformation in aquatic sediment systems
OECD 308, Regulation (EC) No 440/2008, C.24

The aim of the study is to measure the transformation and/or mineralisation rate of the test substance and/or its transformation products in aquatic sediment systems, the identification and quantification of transformation products and phase distribution including a mass balance (when labelled test substance is used). For this, two aerobic and two anaerobic sediments are used. The test duration usually is 100 days.

Aerobic mineralisation in surface water - simulation biodegradation test
OECD 309, Regulation (EC) No 440/2008, C.25

Determination of the time course of biodegradation of a test substance at environmental realistic concentrations (< 1 µg/l to 100 µg/l) in a shake flask batch test with natural surface water (fresh, brackish or marine). The low concentrations ensure that the biodegradation kinetics obtained in the test reflect those expected in the environment. The test flasks are incubated in the dark at ambient temperature while shaking under aerobic conditions in at least two levels. At appropriate time intervals either the residual ¹⁴C or the residual concentration of test substance are measured. The test duration usually is up to 60 days.

The laboratory of Hydrotox does not maintain a radionuclide laboratory. Simulation tests are carried out in co-operation laboratories.