Researches Of Anammox Iron Reduction And Quorum Sensing Phenomena

Anaerobic ammonium oxidation (Anammox) is a biological process in which ammonium is oxidized to nitrogen using nitrite as the electron acceptor. Compare to the traditional nitrogen treatment process, Anammox process has the advantages of no need of carbon source, no need of aeration and the low amount of surplus sludge, which has attracted considerable attention from the worldwide. However, the long doubling time and environmental sensitivity have become the choke point on the application of this process. To solve these problems, the iron reduction pathway of Anammox was investigated. New methods of enhancing the metableolic activity and accelerating the start-up of Anammox were developed through exploring the effects of quorum sensing on Anammox activity and preparing influent water from Anammox granular sludge reactor (AGSR) supernatants. The effects of quorum sensing signals on keeping the stability of Anammox granules and keeping the activity of preserved Anammox bacterias were also analyzed. The innovative findings in our research have been made as follows:(1) The iron-reducing capability of Anammox bacteria was investigated in this study. In this study, the highest iron-reducing activity of Anammox bacteira could be achieved with Fe(III)-NTA as electron acceptor and formate as the electron donor at pH7. Similar to other iron reducers, about 80% of the iron reductase in Anammox bacteria was located in the membrane fraction,20% iron reductase was located in the soluble fraction and 51% iron reductase was located on the anammoxosome. When the iron-reducing pathway and the nitrogen removal process of Anammox were coupled, the nitrogen removal process could not be affected. However, the Fe(II) content reduced by Anammox bacteria was only 7.06% of the control group.(2) Quorum sensing signaling molecule N-dodecanoyl homoserine lactone (C12-HSL) was detected in the supernatant of an Anammox granular sludge reactor (AGSR). Using C12-HSL containing AGSR biomass supernatant prepared influent water to domesticate bacteira could reduce the start-up time of Anammox process from 80 to 66 days. Moreover, the nitrogen loading rate (NLR) was also enhanced to 1.6 times of that in the control reactor. Additionally, AGSR supernatant could also enhance the secretion of extracellular polymeric substances (EPS) and the enrichment of Anammox bacteria. The microbial community parameters could also be effected.(3) Quorum sensing signal could affect the Anammox nitrogen removal activity. Moreover, the strength and stablilitiy of Anammox granules could also be affected through regulating the EPS secretion. Degradation of AHLs using vanillin and AHLs-acylse exposure could lead to the depression of specific Anammox activity from 178.48 mg N/g VSS·d to 156.66 mg N/g VSS·d. The crude enzyme activity of Anammox bacteria also decreased from 2.33μmol cytochrome c/min/mg protein to 1.63 and 1.47μmol cytochrome c/min/mg protein. The degradation of AHLs could lead to the depression of strength and stability of Anammox, which was mainly due to the EPS reduction and the changes of PN/PS ratio.(4) Quorum sensing signals could sustain the biomass activity and Heme c content of Anammox bacteria which were preserved for long-term period. With the preservation period of 90 days at 20℃, adding 10 mg/L C12-HSL into the Anammox flocs, the SAA and crude enzyme activity were higher (6.13% and 27.73%) than that in the control group. Similarly, adding 1 g/L porcine kidney acylase I into the Anammox granues, the SAA and crude enzyme activity of Anammox granules were only 86.24% and 86.44% of the control. Moreover, the quorum sensing signals could also help to keep the Heme c content in Anammox bacteria. The Heme c content of Anammox flocs adding with 10 mg/L C12-HSL was 27.03% higher than that in control group. However, the Heme c content of Anammox granules adding with 1 g/L porcine kidney acylase I was only 59.65% of the control.