Effect of vapor-phase bioreactor operation on biomass accumulation, distribution, and activity: Linking biofilm properties to bioreactor performance

Excess biomass accumulation and activity loss in vapor-phase bioreactors (V PBs) can lead to unreliable long-term operation. In this study, temporal an d spatial variations in biomass accumulation, distribution and activity in VPBs treating toluene-contaminated air were monitored over a 96-day period. Two laboratory-scale bioreactors were subjected to a toluene loading rate of 45.8 g/m(3)-h with one VPB operating in a unidirectional (UD) mode and a second identical VPB operating in a directionally switching (DS) mode. In the UD bioreactor, the contaminated air stream was continuously fed to the bottom of the reactor, while, in the DS bioreactor, the direction of the co ntaminated gas flow was reversed every three days. Overall, the DS system p erformed better with respect to biomass distribution and microbial activity across the bioreactor, resulting in more stable bioreactor performance. In contrast, most of the biomass accumulation and activity was confined to th e front half of the UD bioreactor column which caused high pressure drops, rapid activity loss and eventually toluene breakthrough. A carbon balance r eveals that excess biomass accumulated continuously in both bioreactors, an d biomass yield coefficients were very similar (0.59 g dry biomass/g toluen e for the UD and 0.63 g dry biomass/g toluene for the DS). The viable bioma ss population remained relatively constant in both bioreactors over the ope rational period, while the inactive biomass fraction steadily increased ove r the same time frame. Biodegradation activity determined by the dehydrogen ase enzyme activity assay was found to be a function of biomass accumulatio n and reflected pollutant removal profiles along the columns. In addition, biomass activity correlated well with the toluene-degrading fraction of the total bacterial population. (C) 2000 John Wiley & Sons, Inc.