Enhanced Denitrification Of The Secondary Effluent From Municipal Wastewater Plant By Combined MBBR And Nanofiltration Technology

As we all know,China is a typical agricultural country,and ammonia nitrogen is the primary pollutant in Chinese surface water pollutant.With upgrading the effluent quality standard during China's "Twelfth Five-Year Plan" aimed at the sewage treatment plant,the water quality standards of urban sewage treatment plants have been gradually increased now,which put forward higher and higher requirements for the treatment process of urban sewage treatment plant,urgent looking for a cost-effective treatment process in order to making the effluent quality suits the national emission standards.In this paper,we made MBBR(Moving Bed Biofilm Reactor)-nanofiltration combined bioreactor technology,studied the denitrification performance of secondary sedimentation effluent from urban sewage treatment plant.According to analyzing the basic properties of the fillers used in MBBR,we studied the effecting factors of the oxygen transfer efficiency,and believed the best filling rate was 40%.In addition,the proper operating parameters for nanofiltration membrane were also acquired,and we studied the effect on the operating pressure to the membrane flux and rejection rate at the same time.It shows that the nanofiltration membrane has effect on the removal to COD and NH4+-N,whose rejection rate was definitely relied on the membrane's pore size and the concentration of contaminants,which means increasing the concentration of COD and ammonia nitrogen to a certain extent can conducive help the pollutants removed.On the basis of the above results,the MBBR reactor was used in the start up experiment,and the operating parameters were optimized by real-time monitoring the concentration of COD,the nitrogen and also total phosphorus in the effluent,simultaneously,studied the effect of denitrification to the reactor by adjusting the Dissolved Oxygen concentration and Hydraulic Retention Time.The results showed that when the DO concentration reached 3 mg·L-1and the HRT was 8 h,the MBBR biofilm reactor had the best affect,when we can find the thickness of biofilm in fillers was increased through the microscope clearly,and the respective removal rate to sewage of COD and ammonia nitrogen were 80% and 65%.Finally,the MBBR-nanofiltration combined biological denitrification reactor was designed and operated for a period time,when we continuously monitored the effect of COD and total nitrogen concentration.Besides,the denitrification operation condition in every single period was also been studied,which was found has a better removed affect comparing with the traditional MBBR technology.The removal rate of COD in this reactor can be more than 90% and the removal rate of ammonia nitrogen is 80%,which reached the emission standards of national level A though monitored effluent for a long time.