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

Abstract

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 flow 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.