Study On Nitrogen Transport And Transformation In Biological Aerated Filter

Wastewater biological denitrification is based on the changes of nitrogen valence and nitrogen form in the treatment plant. Finally, nitrogen detaches form water in the form of gas. At present, biofilm denitrification researches mostly focus on macro field, such as filler selection or operating conditions optimization. Due to the lack of test methods, it is difficult to research on micro field in the biofilm. Microelectrode can provide detection on the micron level and high measurement accuracy. It provides strong technical support for in situ detection of biofilm. And that has important significance to establish method of biofilm microcosmic theory.This paper is based on the nitrogen transformation in up-flow biological aerated filter. After installation, it explores the typical optimization conditions of BAF through the control of reactor in different conditions. Then according to the biological aerated filter on typical conditions, it analyses on nitrogen distribution in liquid phase and in biofilm along flow direction using microelectrode technique. At last, it explores the microbial law by electron microscopy and PCR-DGGE technology. The result will provide a theoretical basis for the nitrogen removal process and optimization of biological aerated filter and all the biofilm process.Until the biofilm in the reactor reaches a mature condition, it concludes the typical conditions of BAF reactor: hydraulic retention time is 4h, air/water ratio is 5; carbon/ nitrogen ratio is 3, alkalinity is 50mg/L(Ca CO3) by testing COD, NH4+ and TN concentration under different conditions.By drawing the glass capillary and injecting e ion exchange membrane at its tip and injecting electrolyte internal, the ion selective membrane microelectrodes are made. The Ag/Ag Cl is installed as communication signal wire. Through five concentration gradient tests, it shows that the linear correlation coefficients of NH4+, NO2-and NO3-ion selective membrane microelectrodes Nernst response curve are 0.9947, 0.9939 and 0.9966, which achieves the quantitative analysis requirement.Through the nitrogen distribution test on BAF macro liquid and micro biofilm, it shows that the inner structures of biofilms along flow direction are different. Total nitrogen concentration and COD concentration do not change uniformly with the height change but region differently, which means that different interval contributions of differently on pollution degradation. The biofilm at influent part is at hypoxia or anaerobic environment, which is not suitable for the growth of nitrifying bacteria. The removal of pollutants in this part is mainly on organic matter absorption. There are anoxic zone and aerobic zone in the biofilm at middle part. And it enhances the SND(simultaneous nitrification and denitrification) reaction. The degradation rate of TN reached the maximum at this part. The dissolved oxygen penetrates the biofilm at posterior part. It is under aerobic condition in biofilm at posterior part, which is not suitable for the growth of denitrifying bacteria. SND reaction is gradually stopped. Because of the air and water contacting fully, dissolved oxygen increased to larger value and nitrification is enhanced gradually. NH4+ degradation rate reaches the maximum in this part. Water shows strong oxidation resistance at the effluent part. But the degradation rates of pollutants are slow down due to the reduced amount of filler. Concentrations of pollutants gradually stabilize to the effluent concentration.After the electron microscope observation on the surfaces morphology of different ceramists along flow direction, it concludes microbial biomass on different ceramists shows a decreasing trend. The representative microbial at influent part, middle part and posterior part are filamentous bacteria, bacillus and aureus respectively. According to biofilm population diversity, diversity index at BAF forepart is the highest. The biofilm microbial structure at forepart is the most abundant, which is based on PCR-DGGE.Based on the analysis of biofilm population Dice coefficient, cluster and PCA, it shows that micro environment and microbial population structure in BAF forepart is similar. And the posterior part is similar, too. In the construction of the system of BAF development tree, the main advantage floras of BAF forepart are genus Lacibacterium, genus Lacibacterium, genus Sulfurimonas and genus Epistylis. To the middle part, the main advantage floras are dominant bacteria for Nitrosomonas, genus Epistylis and genus Lysobacter. To the posterior part, the main advantage floras are genus Epistylis, genus Lysobacter and genus Reyranella.