Enhanced The Activity Of Anammox Biomass By Electrochemical Techniques

Recently, noval nitrogen removal processes based on anammox technology have become the research focus in nitrogen removal from varied wastewaters. Compared with the conventional nitrification-denitrification process, there are some advantages of anammox process, such as economic, energy-saving, high-efficiency and environment-friendly. However, extremely slow growth rate of anammox bacteria with a long doubling time causes the longer start-up period, which hinders the development of anammox process in the world. Hence, for the purpose of fast starting up the anammox reactor, it was vital to search for some kinds of technologies to enhance the activities of anammox biomass. In this study, the electrochemical techniques were designed to enhance the anammox activity. Moreover, both the mechanisms of reaction and operation conditions were studied in detail. The main reaserch achievements of this study have been made as follows.(1) External electric field could enhance the activities of anammox biomass under appropriate condition After 160 days cultivation, the external electric field increased the nitrogen removal rate of anammox biomass by 39% when the electric field was 2 V/cm with the application time of 18 h/day. In addition, the optimal application mode of electric field was continuous application of 9 h and the resting time of 3 h. The excess field intensity and application time could inhibit the anammox activity, but the activity could be recovery after the electric field was switched off Furthermore, transmission electron microscope (TEM) observation demonstrated that electric field resulted in the irregular shape of cell and submicroscopic structures, which generated more location of cytochrome c.(2) Three-electrode anammox system was designed to enhance the activity of anammox biomass. The activity of anammox biomass also could be enhanced with the appropriate electric potential difference (EPD) in a three-electrode reactor. The EPD of 0.08 V between the working and reference electrodes showed the best nitrogen removal performance. Under the optimal EPD of 0.08 V, the nitrogen removal rate of reactor 2 (R2, EP applied) reached 0.91 kg-N/m3/d on day 188, which was 25.3% higher than that of reactor 1 (R1, the control). Moreover, SEM observation and extracellular polymeric substance analysis proved that EP application was conducive to the cell growth of anammox bacteria attached onto the surface of cathode. Additionally, it was demonstrated that long-term EP application increased the crude enzymes (HDH, NIR and NAR) activities of 20%-50% and the cell quantities of 20.4% in the bio-electrode anammox reactor. Besides, TEM observation proved the morphological variation of anammox biomass under continuous EP pressure.(3) RGO was used for modifying electrode to apply in anammox reactor. Based on the experimental results, the activity of anammox biomass also could be enhanced with RGO addition. 100 mg/L RGO addition increased the activity of anammox biomass by 17.2% and HDH activity by 1.75 folds. Also, compared with coenzyme Q which was the electron shutter in the enzymatic reaction, RGO possessed the more efficient electron transfer ability. RGO could enhance even replaced coenzyme Q to participate the enzymatic reaction, which was the key reason to enhance the anammox activity with RGO addition. Moreover,100 mg/L RGO addition could accelerate the growth rate of anammox cells, further shorten the startup period of anammox reactor by 26.9%. Furthermore, RGO/PPy electrode applied in anammox reactor could enhance the nitrogen removal efficiency by 37.5%.(4) Electrode-anammox-autotrophic denitrification system was designed to enhance the nitrogen removal efficiency. The nitrogen could be removed successfully by the single electrode reactor coupled with anammox and autotrophic denitrifying process. The optimal voltage applied in coupling process was 1.5 V. The excellent nitrogen removal performance could be obtained by adjusting the ratio of inflent NO2--N/NH4+-N. The best nitrogen removal efficiency reached 99.1% with the influent NO2--N/NH4+-N ratio of 1.5. In the reactor, anammox biomass and denitrifiaction biomass took charge of the nitrogen removal of 79.4% and 19.7%, respectively. Based on the analysis of microbial community, the anammox and autotrophic denitrificationbiomass occupied 43.9% and 22.4% of the total microorganisms in the electrode-anammox-autotrophic denitrification system.