Study On Advanced Treatment And Optimization Control Of Secondary Effluent From Municipal Sewage Plant

The contaminated secondary effluent of WWTP was chosen as raw water in thisresearch. The combined process of advanced treatment was used on removing pollutantfor the standard of landscape water by analyzing secondary effluent. The processoptimization of coagulation sedimentation-O₃-biological sand filter-GAC wasdetermined by contrasted different experiment between front ozone and rear ozone，ordinary sand filter and biological sand filter. The influences of hydraulic loading, modeand intensity of back-washing, initial concentration were analyzed in differenttemperature, pH and dosage of O₃, and definite optimal parameter. Research resultswere as follows.Polyaluminium Chloride （PAC） was used as coagulant in this test. The secondarycoagulation precipitation on pollutants removal effect to achieve the best performanceby the optimal dosage was determined as75mg/L through jar test.Removed of biological sand filter on NH₄⁺-N, CODMnand turbidity was80%,15%,80%achieved stability during the natural biofilm formation. The stable removal rate ofNH₄⁺-N, CODMnand turbidity was the symbol of mature of biological sand filter.Opposite experiment between front ozone and rear ozone，ordinary sand filter andbiological sand filter was researched. Degradation property of front ozone on organicmatter removal better than rear ozone was analyzed. Biodegradability of biological sandfilters on organic matter removal better than ordinary sand filter. Coagulationsedimentation-O₃-biological sand filter-GAC was the best combination process forremoving secondary process was contrasted.Influence of water temperature, pH, back-washing, dosage of O₃, initialconcentration and hydraulic loading on reduction pollutant removal performance bycombined process. It can be get better treatment effect, when hydraulic loading was6m3/（m²·h）, ozone dosing quantity was3mg/L, initial concentration of CODMnwas11mg/L, initial concentration of NH₄⁺-N was15.64mg/L by combination process control.In addition, the backwash mode of biological sand filter adopts the air-water combinedbackwash: the intensity are14L air/（m²·s）, lasting4min, the intensity are14L air/（m²·s）,lasting4min, combined backwashing intensity are12L water/（m²·s）, combinedbackwashing intensity are8L air/（m²·s）, lasting6min, the intensity are12L water/（m²·s）, lasting5min. The hydraulic loading of GAC was5m3/（m²·h）, and the backwash mode ofthe intensity are4L air/（m²·s）, lasting2min, the intensity are8to10L water/（m²·s）,lasting3to4min.The average removal of Coagulation sedimentation-O₃-biological sand filter-GACon CODMn, turbidity, NH₄⁺-N, TN were52.39%,72.44%,93.9%,40.95%，and theconcentration in effluent were5.17mg/L,7.4NTU,2.72mg/L,13.40mg/L. The qualityof effluent conforms to landscape water environment of the urban sewage recycling andbetter than it（GB/T18921-2002）.