Modeling simultaneous autotrophic and heterotrophic growth in aerobic granules

A mathematical model has been developed to describe the simultaneous autotrophic and heterotrophic growth in granule-based sequencing batch reactors (SBRs). Experimental results of a laboratory-scale granule-based SBR are used to calibrate and validate the model. The model is able to simulate the reactor performance and gain insight in autotrophic and heterotrophic growth in the granules. With the established model, the fractions of active biomass (autotrophs and heterotrophs) and inert biomass are predicted to be 55.6% and 44.4% of the total mixed liquid volatile suspended solid, respectively, at a solids retention time (SRT) of 20 days. Biomass content increases with increasing SRT, but active biomass ratio decreases. Autotrophs have no significant effect on the total biomass content, although they play an important role in nitrogen removal. Simulation results also demonstrate the key role of the influent substrate and NH4+-N in governing the composition of heterotrophic and autotrophic biomass in a granule-based SBR. The autotrophs are mainly located on the outer layer of granules, whereas the heterotrophs are present in the center of granules, or on the outer layer of granules.