Culture Of Anaerobic Ammonium Oxidizing (Anammox) Bacteria By Using Cyclic Aeration In Anaerobic Membrane Bioreactor

At present, China is facing increasingly serious problem from wastewater rich in nitrogen. Among new nitrofen removal processes, anaerobic ammonia oxidation (Anammox) process gets more and more attention,owing to its high nitrogen removal rate, low aeration energy requirement,small sludge production, and no external organic carbon addition. However, the long startup period limits its development due to very low growth rate of Anammox bacteria.Aiming at the exising problems of Anammox, a submerged anaerobic membrane bioreactor (SAnMBR) on Anammox bacteria enrichment was developed in this study. The produced nitrogen gas from Anammox reaction was induced by a cyclic aeration system to purge membrane for fouling alleviatation, thus combined SAnMBR with Anammox process. The main experimental results are as follows.(1) The influence of inoculated sludge characteristics on membrane bioreactor startup was investigated, while the impact of self-cycle aeration rate on Anammox bacteria activity and particle size was also studied. The results show that in the membrane bioreactor, when circulating aeration rate reached0.2m3/h and inoculated Anammox granular sludge, the reactor operation could not be stable. While using Anammox flocculated sludge as inoculum, the reactor was successfully operated for69days at35℃. The maximum nitrogen loading rate was1.8kgTN/m·d and specific Aanmmox activity (SAA) was0.463kg TN/kg VSS-d. Total nitrogen removal rate remained at83%. Among the range of0-0.2m3/h for aeration rate, increased aeration had no significant effect on Anammox bacteria activity and particle size.(2) To understand membrane pollution in the anaerobic membrane bioreactor, membrane fouling situation was investigated at different cyclic aeration rates during the above operation. With the circulating aeration rates at0,0.1and0.2m3/h, the membrane cycles were4,9and37days, respectively. The results illustrate that the application of cyclic aeration system for online scouring the surface of membrane effectively relieved membrane fouling. Compared to without aeration, with the aeration rate at0.2m3/h, the extracellular polymeric substance (EPS) significantly reduced. Although aeration could not avoid membrane fouling, with the increase in aeration rate, membrane fouling could be effectively alleviated, and the optimum aeration rate was0.2m3/h. (3) The Anammox bacteria growth kinetics in the membrane bioreactor were also investigated by using Lawrence-McCarty model. Experimental results show that the real yield Anammox bacteria (YT) was0.17mg VSS/mg NO2-N, attenuation coefficient (Kd) was0.01d-1. Anammox bacteria could grow fast in the membrane bioreactor. Compared to other reactors (such as SBR, UASB), SAnMBR had the ability to increase sludge concentration shorten the startup time, thus achieve better enrichment. During the experiments of growth kinetics, with the circular aeration rate of0.2m3/h at room temperature, the system was successful operated in93days, and the maximum nitrogen loading rate was3.95kg TN/m3·d with the TN removal efficiency higher than80%. The successful startup at room temperature can further save operating cost.The sucessful operation of the SAnMBR for Anammox bacteria enrichment could provide a practical approach for engineering application. With the cyclic aeration using self-produced nitrogen gas could effectively alleviate membrane fouling.