Biomass control in waste air biotrickling filters by protozoan predation

Two protozoan species as well as an uncharacterized protozoan consortium we re added to a toluene-degrading biotrickling filter to investigate protozoa n predation as a means of biomass control. Wet biomass formation in 23.6-L reactors over a 77-day period was reduced from 13.875 kg in a control biotr ickling filter to 11.795 kg in a biotrickling filter enriched with protozoa . The average toluene vapor elimination capacity at 1 g/m(3) toluene and 64 m(3)/(m(3).h) was 31.1 g/(m(3).h) in the control and 32.2 g/(m(3).h) in th e biotrickling filter enriched with protozoa. At higher toluene inlet conce ntrations, toluene degradation rates increased and were slightly higher in the biotrickling filter enriched with protozoa. The lower rate of biomass a ccumulation after the addition of protozoa was due to an increase of carbon mineralization (68% as compared to 61% in the control). Apparent biomass y ield coefficients in the control and enriched trickling filter were 0.72 an d 0.59 g dry biomass/g toluene, respectively. The results show that protozo an predation may be a useful tool to control biomass in biotrickling filter s, however, further stimulation of predation of the biomass immobilized in the reactor is required to ensure long-term stability of biotrickling filte rs. (C) 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 62: 216-224, 1999.