The Typical Inhibition Of Anammox And Its Control Strategy

Anammox is a novel and cost-effective biotechonology for nitrogen removal from wastewater. However, the difficulty of Anammox sludge cultivation and the inhibition of inhibitor, such as phenol, copper (Ⅱ), oxytetracycline (OTC) and S2-in wasterwater hinder the commercial applications of Anammox process. In this study, the effluent sludge from a high-rate Anammox granular reactor after storage for different time was used to seed Anammox reactors, a maximum nitrogen removal rate (NRR.) of more than20kg-N·m-3·d-1was achieved in a relatively short period by optimizing the process start-up strategies. Scanning electron microscopy (SEM) observed the spherical and ellipsoid Anammox bacteria which were dominant in the Anammox granular sludge. The values of half inhibitory concentration (IC50) of phenol, copper (Ⅱ), OTC and S2-on Anammox of861.7,14.6,682.6and288.3mg·L-1, respectively were calculated by batch test. In continuous flow tests, the NRR of control reactor was stably increased from10.5to21.3kg-N·m-3·d-1. As the inhibitory effect of phenol, the NRR dropped by12.1kg-N·m-3·d-1in a short period of23days, the nitrogen removal ability only recovered to the original level at a low influent phenol concentration (12.5mg·L-1) within86days. SEM observed a bacillus in the Anammox granular sludge exposed to phenol, but not found in the sludge of control reactors. The Anammox nitrogen removal ability was reduced by98.0%at a copper (Ⅱ) concentration of5mg·L-1, and only recovered to13.1kg-N·m-3·-d-1after an operation for more than100days feeding an influent without any copper (Ⅱ). Copper (Ⅱ) could destroy the cell integrity rapidly by damaging the cell membrane, and SEM observed the cell-lysis phenomenon. Influent with50mg·L-1OTC made the NRR decreased from12.4±1.3to2kg-N·m-3·d-1within26days; the Anammox nitrogen removal performace was not improved remarkably within nearly two months even gradually reducing influent OTC concentration to0mg·L-1. An agglomerate phenomenon on the surface layer of the granular sludge with a significant increment of exocellular polymeric substance was observed by SEM. The nitrogen removal ability of non-acclimatized Anammox mixed culture reduced by50%within a short period of13days in the presence of32mg·L-1S2-in the influent; while the nitrogen removal ability only reduced by17.2%within18days at the S2-concentration of40mg·L-1after sludge acclimatization under the same NLR. In addition, cell-lysis phenomenon caused by the four inhibitors mentioned here was all observed in the Anammox mixed culture by TEM. Anammox inhibition can be controlled by proper measures. Substrates concentration and loading rate control, pH adjustment and free ammonium regulation, sludge acclimatization as well as inhibitors concentration regulation are all effective at recovering and stablizing the Anammox performance. The joint toxicity of OTC and copper (Ⅱ) on Anammox mixed culture was antagonistic, while the interaction between OTC and S2-, or phenol and S2-was generally toxicity enhancement. The joint toxicity of phenol and copper (Ⅱ) was phenol level-dependent, at a high phenol level of300mg·L-1, the joint toxicity was antagonistic, at a low phenol level of75mg·L-1the toxicity was enhancement. The joint toxicity tests of OTC, copper (Ⅱ) and NO2--N found that the primary and secondary order of the Anammox active inhibition factors was NO2--N>Cu (Ⅱ)> OTC.