Study On Nitrogen Removal Characteristics Of Anaerobic-oxic Biological Filter Conbination Process For Municipal Sewage Treatment

With the urbanization intensifies in China, many municipal sewage treatment plants need to built inside the city. Most of the municipal sewage treatment plants built in China was adopted the activated sludge process. Activated sludge process was not suitable the municipal sewage treatment plants which need to built inside the city,because its area is too big and stink when running out. The effluent was demand to meet the National discharge standard of level 1-A (GB 18918-2002) in china for many municipal sewage treatment plants which need to built inside the city. It is impossible to reach for the general activated sludge process, especially its total nitrogen effluent limitations.Anaerobic-oxic biological filter conbination process was designed combined with the advantages of A/O biodenitrification technology and biological aerated filters. Its area is small, management is convenient, effluent is high standards, no odor and so on which was similar with biological aerated filters; it had a high removal efficiency to total nitrogen which was similar with A/O biodenitrification technology. The removal characteristics of anaerobic-oxic biological filter conbination process for municipal sewage treatment were in-depth studied in this paper, such as cultivation and acclimation of biofilm, the characteristics of biofilm and backwash sludge, efficiency factors of nitrogen removal, preparation of new filter, application efficiency of the process, fluid dynamics and substrate removal dynamics research. The main conclusion briefly described as follows:At first, the startup method and removal characteristics of pollutant in startup stage have been studied. The method of startup of intermittence inflow at first then continuous inflow, gradually increase the flow and reflux ratio was adopted. The effluent of the system achieved COD about 40mg/L, ammonia nitrogen about 4mg/L, total nitrogen about 15mg/L after 30days of cultivation.Then, the process parameters of anaerobic-oxic biological filter conbination process were systematic studied, such as DO, backwash, reflux ratio, temperature, hydraulicload, anoxia /aerobic volumetric ratio,and so on. Results were shown that: The removal efficiency of system to pollutants achieved the best, when the DO was controlled in 3.0~3.5mg/L, the reflux ratio was controlled in 130% and the anoxia /aerobic volumetric ratio was controlled in 1:1.5.When the hydraulicload was increased, the pollutants of effluent was increased.When the hydraulicload recovered, the pollutants of effluent would recovered in short time.The backwash cycle was 5 days (anaerobic biological filter) and 10 days(aerobic biological filter) in reactor test. Backwash had a great influence to both aerobic biological filter and anaerobic biological filter. But it could be basic recovery the level before backwash in a short time (130~150 minutes).When the temperature droped, the nitrification, denitrification and simultaneous nitrification denitrification were all had great influence, and the most heavily influence of low temperature was nitrification.The SND rate is low in anaerobic-oxic biological filter conbination process.It reached about 12.00% in the best condition taking above. DO, backwash, reflux ratio, temperature, hydraulicload and anoxia /aerobic volumetric ratio all had influence on SND. It has good removal efficiency for COD, ammonia nitrogen and total nitrogen in the system under the process conditions like that water flow 8.5L/h, eflux ratio 130%, dissolved oxygen 3.0~3.5mg/L and water temperature 19~25℃.The characteristics of biofilm and backwash sludge were studied. The biological membrane and biological phaser, microstructure of filter were analyzed. When the characteristics of backwash sludge were studied, the ability of adsorb ammonia nitrogen was found. The adsorption property of backwash sludge in aerobic filter was stronger than that in anaerobic filter. The liveness of backwash sludge had little influence to the adsorption of ammonia nitrogen. Metal salt coagulants had little influence to the adsorption of ammonia nitrogen,too.Temperature had a great influence to the performance of nitrogen removal. Improve DO (increased to 4.0mg/L), improve reflux ratio (increased to 150%) properly and extended backwash period (anaerobic filter 10d and oxic filter 17d) could improve the denitrification efficiency of system when the temperature was low. Using the three methods meanwhile in low temperature had even more significant improvement role to nitrogen removal. The effluent of the system achieved ammonia nitrogen about 7.70mg/L, total nitrogen about 15.25mg/L at that time.The anaerobic-oxic biological filter conbination process was applied in practical engineering project. Problem, reason and solution in operation period in application project were researched by the field experiment.Conversion ways and efficiency for nitrogen in practical engineering project were researched. The efficiency of adsorption of ammonia by backwash sludge was about 7.22%, the efficiency of nitrification in aerobic biological filter was about 72.30%, the efficiency of denitrification in anaerobic biological filter was about 46.97% and the efficiency of SND in aerobic biological filter was about 13.65% in practical engineering project.This technology had high removal rate of nitrogen to the municipal sewage. The effluent could meet the National discharge standard of level 1-A (GB 18918-2002) in china whatever low or normal temperature.At last, a fluid dynamics model was built based on filtering jams model in biological filter and capillary model in biological filter. The substrate removal dynamics models were built based on Monod equation and micro element method. And the models were analyzed and simulated.