E. Szczyrba1, A. Gąszczak1, G. Bartelmus1, D. Janecki2
1) Polish Academy of Sciences Institute of Chemical Engineering, Gliwice, PL; 2) University of Opole Department of Process Engineering, Opole, PL
MODELLING THE PROCESS OF COMETABOLIC DECOMPOSITION OF 4-CHLOROPHENOL BY THE STENOTROPHOMONAS MALTOPHILIA KB2 STRAIN IN THE PRESENCE OF PHENOL AS THE GROWTH SUBSTRATE
Chlorinated organic compounds make up one of the main groups of environmental pollutants. They were placed on the list of priority pollutants by the American Agency of Environment Protection due to toxicity which they show even in very small concentrations and the ability to bioaccumulate. An example of such a compound is 4-chlorophenol (4-CP). It is a toxic compound, first of all, to the nervous system causing demyelinization of nerve fibres and lowering the concentration of every neurotransmitter. 4-CP is used in industry as a semi-finished product in the synthesis of insecticides, herbicides, preservatives, antiseptics and disinfectants. Its presence in the environment is mainly caused by waste water chlorination and bleaching in textile and paper industries as well as decomposition of herbicides. Information on microbiological decomposition of chlorophenols can be found in literature, however, only very few microorganisms are able to use them as the only source of carbon and energy; most often they are transformed in cometabolic processes. Kinetics of cometabolic transformations can be a limiting stage in the sewage treatment processes and soil bioremediation, thus, the necessity to develop mathematical models describing the rate of the process. The kinetics of co-metabolic transformation is often very complex and therefore difficult to describe since the active sites of the enzymes catalyzing the cometabolic reactions can bond with both substrates and therefore various types of interactions can occur among them. A big group of models available in literature was analyzed; starting with the simple models describing cometabolite transformation by resting cells and finishing with very complex models taking into consideration various types of interactions between substrates and biomass. Our own experimental database was the comparative basis for the analyzed models. It refers to cometabolic biodegradation process of 4-CP by the Stenotrophomonas Maltophilia KB2 strain (coming from Faculty of Biology and Environment Protection of the Silesian University of Katowice) in the presence of phenol as the growth substrate. It required 4 series of research: biodegradation of various doses of pure phenol, biodegradation of various doses of pure 4-CP, biodegradation of 4-CP in the presence of phenol at various concentrations of both substrates and biodegradation of 4-CP by resting cells initially induced by phenol. The growth substrate transformation yield and average growth yield coefficient of phenol were calculated on the basis of this database. Next, using the Runge-Kutt 4th order method, the system of three differential equations (describing the changes in time concentrations of phenol, 4-PC and biomass) was solved and constants of the tested models were estimated by fitting experimental and computational profiles. It was stated that the model taking into consideration the competition inhibition between substrates describes the experimental data best.
Keywords: cometabolism, kinetics ,4-chlorophenol, phenol