Study On Three-Stage AO-Advanced Process For More Stringent Standard Sewage Treatment

Shenzhen requires that the effluent pollutants from sewage plants reach the quasiclass IV in Surface Water Quality Standard.In other words,the indicators except for TN and SS reach class IV in Surface Water Quality Standard.Therefore,the sewage plant urgently needs a cost-effective scheme for upgrading the process.The three-stage AO process is a new attempt.Although it has been applied in engineering,its process mechanism,process potential,operational stability and regulation strategies lack systematic research.This paper taken urban sewage treatment with high discharge standard in Shenzhen as the goal,systematically studied the three-stage AO process mechanism and pollutant treatment performance,and tapped process potential.The study screened the appropriate subsequent post-processing units and verified the effectiveness of the combined process.Through laboratory test,the main parameters of the three-stage AO process segment were optimized.The results showed that when the Influent COD,NH₄⁺-N,TN and TP concentrations were 250±30 mg/L,40±5 mg/L,46±5 mg/L and 3.5±0.5 mg/L,respectively,only the COD and NH₄⁺-N can reach the standard in the three-stage AO process under the optimal operating conditions.The results showed that the optimal hydraulic retention time was 12 h,the inlet ratio was 5:3:2 and the sludge reflux ratio was 80%,respectively.The process used a one-stage nitrating solution reflux and the reflux ratio was 50%.In order to ensure that other indicators?TN,TP and SS?of the effluent reach the standard,the paper researched the deep nitrogen removal,phosphorus removal and SS removal units to match the three-stage AO process section.The deep bed filter was supplemented with methanol as a carbon source for denitrification.The influent C:N and hydraulic retention time were 3:1 and 0.3 h,respectively.Simultaneously,the deep-bed filter system's TN effluent concentration was less than 10 mg/L.Deep phosphorus removal process was chemical phosphorus removal.The study compared the operating efficiency of simultaneous chemical phosphorus removal and post chemical phosphorus removal.The results showed that simultaneous chemical phosphorus removal had obvious advantages.Adding 20 mg/L of poly aluminum chloride in the aerobic III zone of the three-stage AO process,the effluent TP concentration was less than 0.3 mg/L.Adding cloth media filter after the three-stage AO combination process.The flux was 5 L/?m2·h?to ensure that the effluent SS concentration was lower than 5 mg/L.A "three-stage AO process+simultaneous chemical phosphorus removal+deep-bed filter+cloth media filter" combined process was constructed.The study examined the removal effect of the combined process on the pollutants and the changes in sludge properties.After 30 days of continuous running experiments,the results showed that the combined process was stable.The effluent concentrations of COD,TN,NH₄⁺-N,SS and TP were 17.6±2.2 mg/L,8.40±0.73 mg/L,0.28±0.14mg/L,4±1 mg/L and 0.19±0.06,respectively.The effluent water quality reached the requirements of Shenzhen for more stringent wastewater discharge standards.