Accelerating the rate of cometabolic degradations requiring an intracellular electron source-model and biofilm application

This paper applies our recently acquired knowledge of the large and systematic changes in internal reducing power to controlled changes in the cell's primary electron-donor and -acceptor substrates. The systematic cellular responses of the NADH/NAD ratio is incorporated into kinetic equations for reductive dehalogenation and oxygenation reactions. Results show that the external donor and acceptor concentrations strongly affect the percentage removal of hazardous compounds. The simplest strategy for maximizing the efficiency of reductive dehalogenation is to maintain a saturating concentration of the primary electron donor, or, as a next best alternative, to minimize the concentration of electron acceptors. For mono- or dioxygenation reactions, consistently high percentage removals can be achieved when the concentrations of both primary substrates are high. Removals of carbon tetrachloride in denitrifying biofilm experiments are in perfect accord with the model predictions for reductive dehalogenation. They show a dramatic increase in percentage removal when the primary electron acceptor (NO₃^-) is removed from the reactor and a substantial decrease when the electron donor (acetate) is removed. Thus, the biofilm experiments verify that biodegradation reactions can be accelerated dramatically by manipulation of primary donor and acceptor concentrations and in a manner consistent with modeling predictions based on the internal reducing power.