Extended mixed-culture biofilms (MCB) model to describe integrated fixed film/activated sludge (IFAS) process behaviour

摘要

This paper presents how, in a calibration process, different assumptions regarding the standardnMixed-Culture Biofilms (MCB) model were able to match the average results at a continuousnJohannesburg pilot plant (comprising two aerobic reactors, AE1 and AE2), but failed to match thenbatch test results of either the rate of endogenous carbonaceous oxygen uptake (OUR) or thenrate of nitrate production (NPR). Under the first assumption, where attachment and diffusion ofnparticulate components were not used, the OUR in the biofilm of the first aerobic reactor (AE1)nwas too low due to the absence of slowly biodegradable COD (XS) attachment flux. In a secondnassumption, where high diffusion and attachment coefficients were used, the NPR in the biofilmnof the AE1 reactor exceeded the experimental value due to the high attachment flux used fornnitrifiers (XA) and the low competition for space from XS and heterotrophic bacteria (XH). The onlynway to match all the experimental results was through the use of a higher attachment coefficientnfor XS in the first reactor (AE1), but this was considered unreasonable. Hence, an extended modelnwas developed where a colloidal state, which interacts at the same time with the flocs and thenbiofilm through attachment-detachment processes, is distinguished. This model allowed thenexperimental results to be matched, but using the same value for the attachment coefficientsnof all particulate components.