Characteristic Research Of Baf For Municipal Wastewater Treatment And Process Inpeoment

Water pollution is one of the most serious environmental problems in China With the development of economy and the improvement of people's living standard, the contradiction between the polluted source water and people's demand for living has become increasingly obvious. Biological aerated filter (BAF), which includes biofilm and activated sludge, is a reactor with double functions. Therefore, BAF has great application potential in the secondary treatment of municipal wastewater.This purpose of my dissertation is to provide a comprehensive research on BAF. First, evaluation was conducted among different filter media. Structure characteristic parameters such as specific surface area, pore volume, connectivity rate, surface characteristic parameter, mechanical characteristic parameter, connectivity rate, surface characteristic parameter, mechanical characteristic parameter of 10 kinds of media were analyzed. The adsorption characteristic parameters including iodine adsorption parameter, sub-methyl-blue adsorption parameter and tannic acid adsorption parameter were also investigated. According to these adsorption parameters, a new characteristic parameters-water adsorption per unit and biological compatibility were obtained, which could truly reflect the ceramic parameters in practical operation and was repeatable in parallel tests. Filled with practical wastewater, the treatment efficiency of different kinds of ceramisites was studied. It indicated the pore volume, 2-50nm pore volume, water adsorption per unit have a preferable relevance with the the treatment efficiency. Further, Synthesis Index of Ceramics Evaluation (SICE) of the specific ceramic filter media that used in urban wastewater treatment was founded. The SCEI could be used as a basis for the choose and evaluation of ceramisite and thus promoting the establishment of the national BAF filter media standard and providing guidance for the development of BAF process.In order to determine the practical operational parameters of BAF, pilot-scale experimental model was established in Taiping wastewater treatment plant. First, the effects of different flow patterns and start-up methods on the efficiency of the BAF reactor were investigated. It was suggested that the method of artificial bacteria delivery was better than natural enrichment and activated sludge addition whether on start-up time or the subsequent treatment efficiency. For removal efficiency of various pollution indexes, it indicated that different removal efficiencies of BOD5, ammonia-nitrogen, total nitrogen, and total phosphorus appeared at different heights. Through the adjustment of operational parameters, removal efficiency variations caused by hydraulic loading, gas-water ratio and temperature were studied. It suggested that when the gas-water radio was 6:1 and upflow velocity was 3.0m/s, the best treatment effeciency was achieved. Also, with the investigation of design parameters, design parameters of BAF suitable for China was obtained, which provided solid theoretical guidance and relevant standards for BAF application. Finally, the effects of back washing on the whole running reactor were discussed. With 20 days running, the reactour requried back washing with gas rate 10 L/ (m~2·s), water rate 4 L/ (m~2·s) and back washing time 15min. Then the system recovered rapidly and performed the best.A microorganism, as an important component of the BAF system, has significant influences on the treatment efficiency of the BAF through their function and activity. Researches on the formation mechanisms of the biofilm demonstrated that interception and adsorption were closely relevant to biofilm formation. Investigation on the characteristics of microbial community pointed out that the succession pattern of indigenous microorganisms and foreign microorganisms after the inoculation of bacterial agent. Furthermore, the diversity and activity of microbial community of BAF were analysed and it showed that microbial community structure changed at different heights. Combined with the different removal efficiency at different heights, it presumed that different microorganism existed along different heights, which provided microbial basis for the design and operation of BAF.Based on the above results, ceramisite were modified Fe spreaded on its surface to enhance the removal of suspendeded solid (SS) and colloidal substances. As a result, the surface area, Zeta potential and pH were changed by chemical deposited to original ceramisite with Fe. The modified ceramisite was efficient for SS removal. Meanwhile, through increasing biological activity material , changing ratio of material composition and adjusting the method of ceramisite baking, microbe-promoting ceramisite was developed. This kind of ceramisite could improve the growth and reproduction of microbes, and could also promote the growth of aerobic denitrifiers and denitrifying phosphorus removal bacteria which were hard to grow and had narrower niche. Meanwhile, improved process for practial application was developed for two new types filter materials: two-stage BAF which had two stage water inflows. The first stage was to remove SS and COD by Feceramisite. The second stage was to remove total nitrogen and total phosphorus by microbe-promoting ceramisite. The effluent of this BAF process could meet Criteria B of LevelⅠof the national discharge standards of municipal wastewater and have a great application potentiaol.