Performance of treating wastewater and anti-shockloading in oxic-settling-anaerobic (OSA) process for minimization of excess sludge

Efficiency of pollution degradation, performance of activated sludge, effect of temperature fluctuation and recalcitrant organic compounds on system stability were investigated in OSA process for minimization of excess sludge. CAS process and OSA process were run with synthetic wastewater for 240 d. The results indicate that the OSA process excels the CAS process as a whole. COD removal efficiency in OSA process was slightly more than that in CAS. Removal efficiency of nitrogen and phosphorus could be enhanced to 42.58% and 53.84% respectively. Biological phosphorus accumulation in aerobic sludge from OSA and CAS were 2.69g and 1.11 g per 100 g dry sludge, which further approved biological phosphorus removal in OSA process. Because of alternative aerobic and anaerobic environment in OSA process, sludge settleability and activity are improved. SVI in OSA process was 97 averagely. SOUR and dehydrogenase activity of sludge in OSA were higher appreciably than those in CAS. Protein concentration was higher above 1.69 mg · g^-1 and polysaccharide concentration was lower 6.7 mg · g^-1 in OSA sludge than those in CAS, which confirms the effect of anaerobic tank on sludge performance and microorganism diversity. Lower polysaccharide concentration in OSA sludge improves the settleability. Contrasting to CAS process, OSA process is more sensitive to impact of p-nitrophenol(PNP) and more inactive to temperature fluctuation. Temperature fluctuation led to an increase of the concentration of GOD, NH₄⁺-N, SS in effluent while sludge production Y_MLSS/COD) was reduced to 0.403 mg · mg^-1 and 0.227 mg · mg^-1 in CAS and OSA. When concentration of PNP was increased abruptly to 10 mg · L^-1, biological nutrient removal was ceased in OSA process. Once OSA system is impacted, it is difficult to restore.