The Effect Of Sulphate Reduction On Sludge Settleability In Biological Selector In Sewage Treatment System

There contains more or less sulfate in landfill leachate or industry waste water, while the concentration of sulfate was about 20～100mg/L commonly in the sewage wastewater, and the industry wastewater will increase the concentration of sulfate. The sulfate will deoxidize to sulfide in the anaerobic treatment which will increase filamentous bacteria and cause filamentous bulking in the following aerobic stage. The anaerobic biological selector combined with the aerobic sequencing batch reactor(SBR) was employed in this experiment to study the effect of sulphate reduction on sludge settleability .The results were as shown:(1) Filamentous bulking of actived sludge was often influenced by many factors, such as sludge load, dissolved oxygen, nutrient as well as influent sulfide concentration. The floc settleability of actived sludge was perfect with the SVI lower than 100mL/g and MLSS 2000mg/L at 3h aeration phase, 1h settle phase. Meanwhile, the removal efficiency of COD, ammonia and phosphate were 86.7%, 99.2%, 98%, respectively.(2) Sarcodina, Ciliated protozoa, Rotifer, Vorticella and Epistyl were observed in turn during the cultivated of sludg which demonstrated that well treating efficiency can be achieved. But increasing the DO concentration to some extend, the aeolosma hemprichii can occur in the reactor, which effected biomass and treating efficiency.(3) With the increasing of influent sulfate and HRT, the effluent concentrate of sulfide increased in the anaerobic biological selector. The in the anaerobic biological selector was influenced by influent sulfate and HRT. The optimal effect of sulfate reduction could be obtained when influent sulfate was 250mg/L and HRT was 60min with the effluent sulfide concentration was 16.83mg/L and sulfate reducing rate was lower than 20.20%. (4) Activited sludge filamentous bulking will be influenced by influent sulfide concentration, while anaerobic biological selector was followed by the aerobic biological reactor. There was a sign of filamentous bulking if the influent sulfide concentration was 1 ～2mg/L and the SVI was 150mL/g. With the increasing of the influent sulfide concentration continuously upwards 3mg/L, lots of filamentous bacteria can be observed by microscopy and the SVI was over 300mL/g. When the sulfide concentration was above to 5mg/L, the SVI was higher than 900mL/g and owing to this high concentration of sulfide, the sludge settleability got worse leading to a high effluent SS and badly treating efficiency.(5) The settle performance can be affected by the influent sulfate concentration and HRT. At the same HRT 60min, When the sulfate concentration was 85mg/L, filamentous bulking became appeared and the sulfate concentration increased to 125mg/L, there was a great lot of filamentous bacteria in the reactor; when the sulfate concentration was 250mg/L and HRT reduced to 20min, biomass was lossed seriously and the treating efficiency declined(6) Vorticella and Epistylis were still existed in the filamentous bulking reactor, but the treated efficiency was decreased, and the MLSS was lower than 1000mg/L. The removal efficiency of COD, ammonia and phosphate were lower than 80%, 90.8%, 68%, respectively.