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MATHEMATICAL MODELS FOR BIODEGRADATION OF CHLORINATED SOLVENTS: II. MODEL ESTABLISHMENT AND SIMULATION

Chlorinated solvents are degraded through cometabolism as secondary sub-strates due to the fortuitous affinity of the somewhat non-specific catabolic enzymes. Products of cometabolism may be further metabolized, but generally are not able to yield energy or be incorporated into the cell mass.

As a consequence of enzyme non-specificity, enzyme competition inevitably occurs between primary substrate and secondary substrate. Further studies show that non-specific enzymes are mostly inducible; these will not be produced in the absence of primary substrates and are degraded naturally over time. The enzymes are inactivated by the reactive intermediates of the cometabolism. Cometabolic biodegradation of chlorinated solvents may be limited by reducing power also. Hence addition of exogenous reductant can temporarily stimulate the cometabolic degradability.

However, improper control of exogenous reductant may also inactivate microbial system. A comprehensive mathematical model is established on the basis of non-specific enzyme pool and reducing power pool. Non-specific enzyme is considered as key enzyme that controls the whole degradation rate. Reducing power plays an important role in electron and energy transfer in biodegradation.

Major factors in models include production, consumption and regulation of key enzymes, and reducing power in cells. Model parameters were obtained from published literature. The comprehensive model and its simulation of critical cometabolic processes in oxidative biodegradation of chlorinated solvents by methanotrophs will be presented.

Key words: bioremediation, biodegradation, chlorinated solvents, cometabolism