Effect of simultaneous biodegradation of multiple substrates on the extant biodegradation kinetics of individual substrates

A respirometric technique was developed to quantify the extant kinetics for biodegradation of an organic compound by biomass that is simultaneously degrading a complex mixture of substrates. The technique uses a fed-batch feed to supply the mixture of substrates at a rate consistent with the organic loading on the completely mixed activated sludge (CMAS) bioreactor from which the biomass was obtained. The results were compared to results from a batch test wherein the target compound served as the sole carbon and energy source. Results from the fed-batch technique showed that simultaneous biodegradation of multiple substrates caused an increased ability for the removal of the target compound, phenol, although the increase was relatively small. A 7 to 12% increase in the maximum specific growth rate was observed for biomass receiving a fed-batch feed at a rate of one to three times the specific mass how rate to the CMAS system. An increase in the fed-batch feed rate to six times the CMAS rate caused a decrease from the maximum enhancement, which was observed at the threefold rate, indicating that there was an upper limit on the stimulatory effect. Less extensive studies with acrylamide, 4-chlorophenol, ethylene glycol, and m-toluate gave similar results. Because the effects of simultaneous substrate biodegradation were small, single-substrate extant kinetic tests should be adequate for describing the capabilities of a biomass for degrading a particular substrate in a multisubstrate environment.