Study On Enhanced Depth Denitrification Of Sewage By Woodchip-Sulfur Packed Bed Denitrifying Biofilter

In order to further decline the nitrogen concentration of secondary effluent in sewage plant and recover the self-purification capacity of the receiving water,the discharge standards of nitrogen pollutants in China has been more strengthened.Nowadays,since the advanced denitrification treatments are limited by high operation cost,inefficient denitrification rate and easier generation of secondary pollutions,how to develop an efficient,energy-saving and non-polluting denitrification treatment is a quite significant problem to be dealt with in future water treatment.According to the characteristics of secondary effluent with the lack of carbon source,an improved denitrifying biofilter,filled with a mixture of woodchip and sulfur,was established to measure the nitrate removal in denitrification process and confirm the optimal operating conditions.Furthermore,this study provided an alternative technology for the enhanced treatment of secondary effluent with a lower ration of carbon to nitrogen.The results indicated that the best HRT of the improved denitrifying biofilter was 10 h.Under the condition of optimal HRT and the concentration of the NO3--N in the inflow was 30 mg/L,while the lowest concentration of NO3--N and NO2--N in the effluent could reach 11.5 mg/L and 1.4 mg/L,respectively.It was worth to mention that the accumulation of ammonia process was not occurred.Moreover,the highest SO42-concentration was about 73.8 mg/L.The removal efficiency was 62.3±0.3%,80.1±0.6% and 98.4±0.3% with the influent concentration of NO3--N at 20.5±0.1 mg/L,15.1±0.1 mg/L and 10.1±0.1 mg/L,respectively.The removal efficiency of NO3--N in the improved denitrifying biofilter increased with the reduction of the concentration of NO3--N,which was consistent with that in autotrophic denitrifying biofilter.The cost of their medicaments was similar.Although the removal capacity of the heterotrophic denitrifying biofilter was higher for NO3--N with different concentration conditions,the chemical was also much larger due to the request of sodium acetate.After the water meeting ? A standard was treated by denitrifying biofilter,the effluent could reach the request of ?–level national standard of surface water and its cost was much lower comparing to heterotrophic denitrifying biofilter and reaction products,such as sulfate,reduced substantially comparing to autotrophic denitrifying biofilter.The technique of high throughput sequencing was applied to explore the microbial community structure in three groups of denitrifying biofilter.The microbial diversity in the improved denitrifying biofilter was the highest,as well as its overlap of microbial OTU in biological membrane of woodchip was higher than other samples.The highest abundance of heterotrophic denitrifying bacteria appeared at the bottom,while it was gained at the middle for the autotrophic denitrifying bacteria in the woodchip-sulfur packed bed denitrifying biofilter.In heterotrophic denitrifying biofilter,Thauera,Meiothermus and Acidovorax had the highest abundance,and the abundance increased with the height of the filter.While in autotrophic denitrifying biofilter,it was autotrophic denitrifying bacteria,such as Thiobacillus,had the highest abundance and with the minimum at the top of reactor.Compared to the conventional denitrifying biofilter with the dominance of heterotrophic or autotrophic denitrifying bacteria,the depth denitrification efficiency of the denitrifying biofilter in the woodchip-sulfur packed bed denitrifying biofilter was enhanced under the common efficiency of different denitrifying bacteria.