|Project:||Analysis of routine biodegradation tests|
Biodegradation can play an important role in the removal of chemicals from the environment and influences the predicted environmental concentration. Therefore, biodegradation of chemicals in sewer systems, waste water treatment plants and surface water is an important factor in the procedure of admitting new chemicals. The OECD and EEC regulations require biodegradability of new chemicals to be tested. Test results are divided in three categories: persistent, ready biodegradable and inherent biodegradable. Due to the variety of test methods available, biodegradability may vary significantly among tests. These tests generally do not measure the rate and kinetics of degradation. However, the rate of biodegradation in the environment is crucial in estimating the accumulation of a chemical and in risk assessment. Furthermore, models of e.g. waste water treatment plants are often very sensitive to variations in the assumed biodegradation rate. This explains the need to extrapolate the test results to different environmental compartments. If it is possible to determine and extrapolate a biodegradation rate (and kinetics) from a model and a test under suitable conditions, it might be possible to come to risk assessment schemes based on sound model.
Biodegradation models will be formulated in terms of the Dynamic Energy Budget (DEB) theory. The DEB theory describes substrate uptake, population growth, microbial mass and energy fluxes. It will be used to develop process-oriented models describing biodegradation in different environments (such as waste water treatment plants, surface water or sea).
The aim is to quantify biodegradation in a way that is applicable to a large class of organic compounds. Processes like co-metabolism, sequential use of several substrates as well as growth on multiple substrates will be modeled. Bio-availability and mass-transfer limitations will also be included. The model will analyze the results of standardized biodegradation tests.
A DEB-based model for the degradation of a compound by one species will be formulated. This model will be extended to bacterial consortia and multiple substrates. Adaptation (a selection process) will be included by varying parameters for energetics among species. Different biodegradation tests will be examined to look for important DEB parameters. To model biodegradation according to the DEB theory a test will be chosen or developed to validate the model and estimate DEB parameters. The resulting model will take into account co-metabolism, di-auxic effects, cryptic growth (growth on dead biomass) as well as mass-transfer limitations. The environmental and biological processes will be kept strictly separated. Environmental compartments will be separate model modules.