EFFECT OF SIMULTANEOUS BIODEGRADATION OF MULTIPLE SUBSTRATES ON THE EXTANT BIODEGRADATION KINETICS OF INDIVIDUAL SUBSTRATES

A respirometric technique was developed to quantify the extant kinetic s for biodegradation of an organic compound by biomass that is simulta neously degrading a complex mixture of substrates. The technique uses a fed-batch feed to supply the mixture of substrates at a rate consist ent with the organic loading on the completely mixed activated sludge (CMAS) bioreactor from which the biomass was obtained. The results wer e compared to results from a batch test wherein the target compound se rved as the sole carbon and energy source. Results from the fed-batch technique showed that simultaneous biodegradation of multiple substrat es caused an increased ability for the removal of the target compound, phenol, although the increase was relatively small. A 7 to 12% increa se in the maximum specific growth rate was observed for biomass receiv ing 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 t o six times the CMAS rate caused a decrease from the maximum enhanceme nt, which was observed at the threefold rate, indicating that there wa s an upper limit on the stimulatory effect. Less extensive studies wit h acrylamide, 4-chlorophenol, ethylene glycol, and m-toluate gave simi lar results. Because the effects of simultaneous substrate biodegradat ion were small, single-substrate extant kinetic tests should be adequa te for describing the capabilities of a biomass for degrading a partic ular substrate in a multisubstrate environment.