Study On Nitrogen Removal Performance In Pre-denitrification UBAF Treating Urban Sewage

The pre-denitrification Up-flow Biological Aerated Filter process is a new process that integrates the advantages of the UBAF and A/O processe and removel effective degradation of organic wastewater,at the same time , it has a better performance of nitrogen removal.This paper focuses on the pre-denitrification UBAF for municipal wastewater treatment. The objective of the experiments was to study the influence of hydraulic load,air/water ratio, reflux ratio, organic volumetric loading , NH₄⁺-N volumetric loading, influent temperature and pH. The experimental results showed that the reactor to remove pollutants with higher efficiency.The pre-denitrification UBAF process took about 20 days to succeed in cultivating biofilim using of the method of start-up with inoculate, CODCr and NH₄⁺-N removal rates were stable at 75%.It had remarkable effective to removal organic pollutant and had potential application for nitrogen removel. The experimental results showed that the removal rate of CODCr, NH₄⁺-N and TN in A/O in UBAF with pre-denitrification reactor could reach to 90.97% , 92.73%and 74.52% on average. The effluent quality met the first class standard of "urban sewage treatment plant pollutant discharge standard" (GB18918-2002).With the increasing of hydraulic loading,the removal of NH₄⁺-N and TN within a certain range, it had the best removal of NH₄⁺-N and TN when the optimal hydraulic loading was 1.11m/h. When air/water ratio was 3:1,the removel of TN was best.The increasing of reflux ratio was conducive to the removal of TN within a certain range, it had the best removal of TN when the optimal reflux ratio was 200%.With increased CODCr volumetric loading and NH₄⁺-N volumetric loading, nitrogen removal performance were dropt, but it had a strong resistance to impact load ability of organic volume.Water temperature was the most important factor of removal NH₄⁺-N and TN, when water temperature above 20℃, the removal rate of NH₄⁺-N and TN was better. According to the different influent, the pre-denitrification UBAF reactor needed to backwashing after 5⁷days. The backwashing procedure was: first, the individual air washing strength was 13¹7 L (m2·s), the separate air washing time was 4 min, second, air and water combination backwashing, washing strength with water was 5⁷L (m2·s) and air was 13¹7L (m2·s), the joint washed strength time was 3 min, last, individual water washing with 5⁷L (m2·s) and time was 4 min. For denitrifying bacteria the effect of washing was less than the nitrobacteria's. Pre-denitrifying UBAF was stable in running of treated the wastewater and the effect of denitrifying was smaller. So the capacity of treating would recover in short time. There was about 9 hours when the removing of NH₄⁺-N and TN became normal value. The dynamics equation of the denitrification in the pre-denitrification UBAF reactor as follows: C e = C0 ?e?kθand k = ?12 .204θ+10.239...