Study On Process And Mechanism Of Simultaneous Methanogenesis And Denitrification Using Hybrid Anaerobic Biofilm And Sludgereactor

Simultaneous methanogenesis and denitrification (SMD) as a novel nitrogen removal process has been payed worldwide attention because this process has many advantages such as less need of extra carbon source, short process, easy operation and resistance to high carbon and nitrogen loading. Previous research showed that granular sludge was a feasible approach to realize the coupling of denitrifiction and methanogenesis functional bacteria, but the granular sludge was easily broken up and the reactor was even crashed, when the reactor was run under high nitrogen loading for a long time. In this study, a new hybrid anaerobic biofilm and sludge reactor (HABSR) which was independent developed by us was employed to achieve SMD reaction, at the same time, an upflow anaerobic sludge blanket (UASB) was also comparatively to study the SMD performance of HABSR and UASB. The influence of nitrate concentration on the degradation mechanism of nitrite and COD in HABSR and UASB reactor, and the microbial properties of the sludge and bifilm were also investigated by batch experiments and molecular biological analysis.The experimental result showed that UASB and HABSR can both be used to realize SMD reaction, and the HABSR had stronger resistance ability to the high nitrogen loading. The removal effciency of COD and nitrate were kept around90%and99%, respectively. And the effluent ammonia nitrogen and nitrite nitrogen concentration was stably at about0.5-1mg/L and0.1-1mg/L, respectively.The accumulation of nitrite was proved as the main reason for the inhibition of the SMD performance. The accumation amount of nitrite in granular sludge was found about10times the biofilm in the batch experiments, and the biofilm showed stronger nitrate removal ability.By SEM obervasation and molecular biological analysis, the stratification phenomenon was found in granular sludge of UASB after operation for a period time. The outer layer of the granular sludge consisted of the denitrification bacteria and facultative anaerobic fermentation bacteria, while the inner layer consisted of methanogens and the obligate anaerobic syntrophic acetogen. But for the HABSR, the reaction area was divided into suspended sludge at the buttom and biofilm on the top. The fermentation bacteria and the denitrification bacteria was the only two kinds of fuctional bactoria remained in suspended sludge while the fermentation bacteria, syntrophic acetogen and methanogens was found in biofilm. The dominant population of methanogens was changed from acetic acid nutritional methanogens to hydrogen nutritional methanogens in granular sludge, while the hydrogen nutritional methanogens was also found in biofilm besides the acetic acid nutritional methanogens.