ANAMMOX-based Nitrogen Polishing Process And Its Microbiological Mechanism

ANaerobic AMMonium OXidation(ANAMMOX)has become the focus in the field of biological nitrogen removal from wastewater,due to its high-efficiency,low-cost and environmental friendly features.Although the successful application of ANAMMOX in the treatment of high-strength nitrogen wastewater,its further expansion into the nitrogen polishing of low-strength nitrogen wastewater or slightly polluted surface water faces some serious challenges.In this study,several types of ANAMMOX seeding sludge were compared;the process characteristics of ANAMMOX-based nitrogen polishing were investigated;an enhanced nitrogen polishing process was established by periodic biomass addition;and the microbiological mechanism of ANAMMOX-based nitrogen polishing was analyzed.The main results are as follows:1)Different types of ANAMMOX sludge were compared for nitrogen polishing,and the sludge with high performance as well as its cultivation way were discovered.All the five different types of ANAMMOX seeding sludge(denoted as AS-1?AS-5),which originated from eutrophic,facultatively eutrophic and oligotrophic habitats,could be applied to nitrogen polishing,reducing the Total Nitrogen(TN)concentration from?15 mg·L^-1to lower than 3 mg·L^-1.The specific nitrogen polishing activities of seeding sludge from the facultatively eutrophic habitats(AS-2 and AS-3)were significantly higher than those from the eutrophic(AS-4 and AS-5)or oligotrophic(AS-1)habitats.AS-2 and AS-3 displayed their high specific nitrogen polishing activities of4.65±0.07 and 4.22±0.18 mg·g^-1-VSS·h^-1,respectively.The good bacterial communities endowed AS-2 and AS-3 with the high efficiency for nitrogen polishing.The dominant Anaerobic Ammonium-Oxidizing Bacteria(An AOB)of AS-2 and AS-3were An AOB-ZJU and Ca.Brocadia sapporoensis,respectively.The abundance of An AOB inside AS-2 and AS-3 was 55.41%and 43.48%,the cell numbers of An AOB(on the basis of 16S r RNA gene number)inside AS-2 and AS-3 were(1.87±0.24)×10¹²and(1.23±0.02)×10¹²copies·g^-1-VSS,and the metabolic activities(on the basis of ribosome number)of An AOB inside AS-2 and AS-3 were(9.51±1.30)×10¹²and(7.10±0.58)×10¹²copies·g^-1-VSS,respectively.It was a feasible way to cultivate ANAMMOX sludge in the facultatively eutrophic habitats for the supply of seeding sludge with high polishing performance.2)ANAMMOX-based nitrogen polishing system was established,and the process characteristics of nitrogen polishing were revealed.The high efficiency of nitrogen polishing was successfully achieved in the polishing Sequencing Batch Reactor(p SBR)system,with AS-2 as seeding sludge and Sequencing Batch Reactor(SBR)as reaction vessel.During the 79-day operation,the concentrations of NH₄⁺-N and NO₂^--N in the influent were 6.20±0.45 mg·L^-1 and 7.96±0.59 mg·L^-1,the TN in the effluent was less than 3 mg·L^-1,and the average Nitrogen Removal Rate(NRR)was 0.054 kg·m^-3·d^-1.However,the long-term operation of p SBR demonstrated that the high effluent quality could not be maintained by itself at the set loading rate.After 80 days,the performance of p SBR deteriorated,whose effluent TN exceeded 3 mg·L^-1 and NRR reduced to 0.045 kg·m^-3·d^-1.The decrease of sludge concentration was the main reason for performance decay.With the aid of process stimulation,several strategies were put forward to maintain the long-term efficiency of p SBR.For instance,the periodic addition of exogenous seeding sludge was proposed to keep the sludge concentration between 0.69 and 0.89 g-VSS·L^-1 and the NRR at 0.05kg·m^-3·d^-1.3)Enhanced nitrogen polishing process was developed,and its high efficiency and stability were verified.The enhanced nitrogen polishing system(p SBR-2 system)was constructed of SBR and AS-2.With the previously proposed strategy(periodic addition of exogenous seeding sludge;adding frequency of once a week;adding intensity of 0.2 g-VSS·L^-1),the high efficiency and stability of p SBR-2 were successfully achieved in polishing synthetic effluent of wastewater treatment plant(TN,?15mg·L^-1).The effluent TN was lower than 3 mg·L^-1,and the average NRR was 0.059 kg·m^-3·d^-1.During the 71-day operation,the contribution of ANAMMOX reaction to the TN removal was 95.85%±3.22%.ADF test and coefficient of variation(CV)analysis indicated the stability of apparent efficiency after 28 days.Periodic addition of AS-2 with a rate of 0.029 g-VSS·L^-1·d^-1could keep sufficient ANAMMOX sludge in the p SBR-2,which was the mechanism for the stability of apparent efficiency.4)Dominant An AOB in the nitrogen polishing system were identified,and the kinetic characteristics of An AOB-ZJU as well as the microbiological mechanism of polishing process were revealed.The dominant An AOB inside the nitrogen polishing system was identified as An AOB-ZJU.The 16S r RNA gene of An AOB-ZJU shared less than 94.5%sequence similarity with those of known An AOB,which suggested a new genus of An AOB.An AOB-ZJU was closed to Ca.Jettenia and Ca.Anammoxoglobus in the phylogenetic tree.The maximum specific growth rate,half-saturation constants for NH₄⁺-N and NO₂^--N,biomass yield,decay coefficient,activation energy of An AOB-ZJU were 0.0034 h^-1,0.20±0.03 mg·L^-1,0.11±0.02 mg·L^-1,0.069±0.010 g-C·g^-1-NH₄⁺-N,0.0012?0.0017d^-1 and 33.71 k J·mol^-1,respectively.The p H and temperature ranges of ANAMMOX activity were 7.5?9.5 and 15?55?,respectively.An AOB-ZJU was featured with moderate affinity for substrates and was therefore classified into facultatively eutrophic An AOB.An AOB-ZJU could tolerate higher temperature(55?)and higher alkalinity(p H,9.5),indicating their survival and possible dominance in the habitats with high temperature and alkalinity.An AOB-ZJU were covered with pili-like appendages,which might help their survival and dominance in the oligotrophic habitats.The nitrogen polishing processes of p SBR and p SBR-2 systems were stimulated by calling the determined kinetic parameters of An AOB-ZJU.The result verified the validity of polishing process model.