SMP variation during endogenous digestion of activated sludge from a MBR process

Under the circumstance of high sludge concentration and low F/M ratio, part of the microorganisms will suffer the shortage of nutrition in the MBRs. The experiment of activated sludge endogenous digestion was conducted to simulate the real existed phenomenon of nutrition shortage. Endogenous digestion performance of sludge taken for a practical A²O+MBR process and variations of soluble microbial products (SMP) were compared between two methods adopting aerobic digestion (AD) and aerobic/anoxic digestion (A/A/D). The results indicated that MLVSS removal could reach 50% and 42% after 20 days' aerobic/anoxic and aerobic digestion, respectively, which meant that A/A/D improved the release and removal of organic substances and nutrients. The concentration of SMP firstly decreased obviously and then increased gradually until reaching a steady level. EEM spectra showed that different fluorescent substances of SMP demonstrated different variation tendency. GPC showed that the range of molecular weight distribution of SMP increased with digestion time, and the amount of organic matter with low molecular weight significantly improved, which indicated that A/A/D was more efficient for the degradation of SMP.