Nitrification and AOB/NOB Populations in Integrated Fixed Film Activated Sludge: Measurements and Modeling

A pilot integrated fixed film activated sludge (IFAS) system and a parallel non-IFAS control were operated for treatment of domestic wastewater primary effluent. They were analyzed for differences in the characteristics of the four biomass phases present (Control suspended, IFAS suspended, and IFAS attached phases in two sequential aerobic reactors) with respect to rates of nitrification (ammonia consumption and nitrite and nitrate production) and population structures. To our knowledge, this study represented the first application of quantitative polymerase chain reaction (qPCR) to study population structures in IFAS systems. The suspended phases of the control systems exhibited similar rates of nitrification (on a per mass basis) in terms of ammonia consumption, although the IFAS suspended phase had significantly higher rates of nitrate and nitrite production. The attached phase in the second aerobic IFAS reactor had significantly higher rates of ammonia consumption and nitrate production than any other biomass source, while the attached biomass from the first aerobic reactor had the lowest rates of ammonia consumption. Quantitative PCR measurements indicated the presence of the AOB Nitrosomonas oligotropha (targeting its ammonia monooxgenase gene, amoA) and the NOBs Nitrospira and Nitrobacter (targeting 16s RNA genes). Both BioWin modeling and qPCR results were in agreement in predicting greater concentrations of the AOBs and the sum of the two NOB populations in the attached phase of a downstream aerobic reactor relative to an upstream reactor attached phase, possibly because of higher biodegradable COD and increased competition from heterotrophs for space in the attached phase of the upstream aerobic reactor.