Effect of soluble microbial products on microbial metabolisms related to nutrient removal

In this study, the effect of soluble microbial products (SMP) on the metabolisms related to phosphate or nitrogen removal of activated sludge was investigated. Two anaerobic–aerobic activated sludge processes were operated, one with a hydraulic retention time (HRT) of 48 h (RunL) and the other 6.4 h (RunS). The longer HRT of RunL was intended to promote the accumulation of SMPs in the supernatant. With the sludge from RunS and the supernatant from both of the runs, supernatant exchange batch experiments (SEBEs) were conducted, in which the acetate uptake rate and phosphate release rates under anaerobic conditions and the phosphate uptake rate under aerobic conditions were measured as these metabolisms are related to enhanced biological phosphorus removal. The nitrification rate was also measured. The statistical analyses of the results from the SEBEs showed that the supernatant from RunL had an inhibitory effect on the anaerobic acetate uptake and nitrification of the sludge from RunS. The cause of which was attributed to SMPs in the supernatant from RunL. As a result, the inhibitory effect of SMPs on nitrification and anaerobic acetate uptake was confirmed.