Comparison of conventional and integrated fixed-film activated sludge systems: attached- and suspended-growth functions and quantitative polymerase chain reaction measurements.

Pilot-scale integrated fixed-film activated sludge (IFAS) and non-IFAS control systems were compared, with respect to overall performance and functional behaviors and microbial population composition in the attached and suspended phases. The suspended phases of the control and IFAS systems exhibited similar rates of ammonia consumption; the attached phase in the second aerobic IFAS reactor had significantly higher rates of ammonia consumption and nitrate production than any other biomass source, and the attached biomass from the first aerobic reactor had the lowest ammonia consumption rates. Quantitative polymerase chain reaction (qPCR) indicated the presence of the ammonia-oxidizing bacteria Nitrosomonas oligotropha and the nitrite-oxidizing bacteria Nitrospira spp. and Nitrobacter spp. Mathematical modeling and qPCR both indicated greater concentrations of nitrifiers in the attached phases of a downstream aerobic reactor relative to the upstream reactor, possibly because of increased competition from heterotrophs for space in the attached phase of the upstream aerobic reactor.