Production of soluble microbial products (SMP) in an anaerobic baffled reactor: Composition, biodegradability, and the effect of process parameters

The composition and biodegradability of effluents from biological treatment plants is of increasing interest due to tightening effluent standards. One of the main constituents of effluents are soluble microbial products (SMPs) produced in the reactor during metabolism and endogenous decay. The objective of this preliminary work was to examine the influence of operating parameters such as temperature, hydraulic retention time (HRT), and organic loading rate (OLR) on the production of SMPs in a compartmentalised anaerobic baffled reactor (ABR) fed a simple sucrose-nutrients substrate. In addition in order to gain greater insight into the SMPs produced, the composition and anaerobic biodegradability of various molecular weight fractions were analysed. It was found that deceasing operating temperature resulted in slight increases in SMP production, a decreased rate of degradation, and hence increases in effluent SMPs. In addition, decreasing HRTs, and increasing OLRs, also resulted in increased effluent SMPs. Quantitatively, between 26 and 48% of the incoming feed COD was converted to SMPs in the first compartment of the ABR more than double that previously reported. Molecular weight (MW) fractionation revealed a bimodal distribution with 25% > 100kDa, and 30% < 1kDa, and all MW fractions were between 62 and 82% degradable. Analysis revealed most of the high MW fraction to be primarily an excreted heteropolysaccharide.