Study On Preparation Of Sulfur Autotrophic Suspended Carrier And Denitrification Of Wastewater By Mixed Culture

The removal of nitrate from domestic sewage with low C/N ratio in our country is a major technical challenge to the industry.In order to meet the total nitrogen requirement,many Sewage Treatment plants add organic carbon sources to enhance the denitrification efficiency.However,this has led to a significant increase in sludge production and carbon emissions,which is contrary to the low-carbon green concept.The sulfur autotrophic denitrification technology has the advantages of low cost,low sludge yield and no secondary pollution.In this study,the sulfur autotrophic suspended carrier was prepared,and the denitrification efficiency of mixed culture of wastewater was studied under different conditions,such as the amount of bacteria in the carrier and the temperature,and the change of carrier structure and the mechanism of nitrogen removal in mixed culture system were analyzed,the high mass transfer performance and high denitrification efficiency of sulfur autotrophic suspended carrier were verified,and a new principle of sulfur autotrophic denitrification was put forward.The main innovative conclusions of this study are as follows:1)The polyvinyl alcohol sodium alginate(PVA-SA)sulfur autotrophic suspension filler was prepared by cross-linking-embedding method with sublimation sulfur(s0)as the sulfur source.It was found that the optimum composition of the fillers was PVA(9wt%),SA(0.12%),Bentonite(2wt%),and bacterial count(25wt%).The PVASA@Bentonite packing has a density of 1.1746-1.2496 g/cm3,a porous network structure with an average pore size of 7.5 mm,and a specific surface area of 3.315 m2/g.It is suitable for fluidized bed reactor and microbial attachment growth,increased the rate of microbial mass transfer.2)The denitrification of PVA-SA@Bentonite packing was evaluated in a continuous batch anoxic tank.The results showed that the denitrification rate of PVASA@Bentonite was 1.5% when the influent temperature was 25 ℃,COD was 60 mg/L,NO3--N was 40 mg/L,C/N was 1.5%,the denitrification efficiency was the best,the nitrate removal rate was 94.41%,the sulfur autotrophic denitrification contribution rate was 27%,and the sulfate formation rate was 78.23 mg/L.After 8 hours denitrification operation,PVA-SA@Bentonite packing density did not change,mechanical strength kept at 100%,sulfur consumption of about 2.03%,packing structure was not damaged,fluidized operation was stable.3)A continuous-flow denitrification experiment was carried out using PVASA@Bentonite suspended carrier to simulate AAO wastewater treatment process in anoxic zone.It was found that the denitrification efficiency of autotrophic-heterotrophic mixed nitrogen removal system was 46.4% higher than that of heterotrophic denitrification system,and the mixed culture system can achieve acid-base complementary,the effluent quality can meet the level a discharge standards.After long-term operation,the density,mechanical strength and S content of the packing decreased,the mass consumption of S was 15.49%,the specific surface area and pore diameter of the packing increased,and the swelling rate was about 25%,the working life of the filler is determined to be about 15 days.