Search Of Simultaneous Denitrification And Methanogenesis In A Single Reactor

Denitrification is an important biological process of the process of the nitrogen cycle on the earth. It is a process that denitrifying microorganism use oxynitride as electron acceptor and eventually change nitrate into nitrogen gas under anaerobic conditions. Due to this biological properties, denitrification plays an important role in the prevention and control of eutrophication of lakes, high nitrate content of groundwater management industrial wastewater treatment. Methane-producing action is a kind of anaerobic respiration. It is the last step of the organic matter degradation, and is the foundation of the anaerobic biological treatment technology. Building in a simultaneous denitrification and methanogenesis system in a single reactor can shorten the wastewater treatment process in high nitrogen wastewater treatment, reduce the amount of processing structures, cut down the cost of disposal, and is of great significance for wastewater treatment.In this paper, we designed several different intermittent experiment, to explore more suitable initial COD/NO3--N ratio and carbon source material for simultaneous methanation and denitrification reaction, so as to further illuminate the mechanism of the competition and coupling between denitrification and methanation. We conducted degradation kinetics analysis on NO3--N and COD degradation process respectively and discussed the specific methane production rate and the specific COD degradation rate. Anaerobic activated sludge taken from wastewater anaerobic treatment technology of the China resources snow brewery was inoculated into the UASB reactor to build up the simultaneous denitrification and methanogenesis system. Then we built a genomic library to analyze the change of the microbial species of the sludge in the reactor before and after building up the SDM system. We ran two reactors at the same time with different carbon sources in the inlet to compare the influence of carbon source on SDM system building processes and final treatment effect under continuous flow conditions. We got the following conclusions:(1) The ratio of the initial COD/NO3--N influenced the SDM system obviously. We compared8:1,10:1,20:1,30:1and40:1, and we found that when the initial COD/NO3--N was10:1the best ratio. The degradation rate of nitrate was over99%, the degradation rate of COD was more than84%and it showed a higher cumulative production of N2and CH4. In addition, denitrification showed a low suppression on methanogenesis at this ratio.(2) The sort of carbon source has a certain influence on the treatment effect. We took sucrose, glucose, sodium acetate and propionic acid as the carbon source of each SDM system, and we found that glucose and sucrose were more suitable as carbon source. The degradation rate of nitrate was more than99%, the degradation rate of COD could reach92.2%and87%respectively, and they both had good gas collection effect. And sucrose is cheaper and more easily to produce.(3) We used a dynamic model proposed by Eckenfelder describing the relationship between the rate of substrate utilization and time under low substrate concentration. After fitting with Origin8.5, we got that the degradation rate constant of nitrate was5.210×10-3(L/mg N03--N)·d-1and the degradation rate constant of COD was3.81×103(L/mg COD)·d-1.(4) We adopted the second Lawrence-McCarty fundamental equation evolved from Monod equation to determine the parameters in the equation. After nonlinear fitting, we got that the maximum specific substrate degradation rate of nitrate nitrogen and COD was5.61mg N03--N/(mg VSS·d) and11.44mg COD/(mg VSS·d) respectively and the rate constant for nitrate nitrogen and COD degradation was462.42mg NO3--N/L and665.65mg COD/L respectively. The yield coefficient of CH4was3.741mL CH4/g COD.(5) We built the SDM system in the UASB reactor by periodically improving the concentration of nitrate in the inlet. System with sodium acetate as carbon source could build SDM system quickly while the degradation rate of TOC and nitrate were high and the gas production effect was good. But sodium acetate system showed a high concentration of TC. System with sucrose as carbon source showed a relatively low degradation rate of TOC and nitrate, but it showed a much lower concentration of TC. The final degradation rate of TOC and nitrate and gas production effect was desirable. Sucrose system may be better with longer processing time. (6) We analyzed the change of the microbial populations in the reactor before and after the simultaneous denitrification and methanogenesis system was constructed using molecular biology methods. The results show that the microbial species in the reactor has undergone great changes. Dominant spieces of archaea changed from Methanobacterium to Methanosarcina. Bacteroidetes dominated in eubacteria instead of Proteobacteria. Biodiversity of eubacteria is significantly higher than archaea.