The Research Of Start-up Optimization And Operation Regulation Of Anaerobic Ammonium Oxidation (Anammox) Reactors

Anaerobic ammonium oxidation (anammox) process can convert ammonium to nitrogen gas under anaerobic conditions with nitrite as the electron acceptor. There is no need for adding external carbon sources or oxygen, avoiding an incomplete conversion of organic matters and resulting in a conspicuous saving in operational costs. As a novel and promising technology for sustainable development and recycling economy, anammox process also could reduce the production of N2O and CO2.Despite the numerous advantages of anammox process, its widespread and large-scale applications are seriously constrained by two disadvantages. Firstly, the start-up time of anammox process is quite time-consuming, which is attributed to the relatively slow growth rate (λmax=0.065 d-1) of anammox bacteria (a doubling time about 11 days). Secondly, the harsh requirement of environmental conditions is needed particularly dissolved oxygen (DO), temperature, pH and organic matter. For instance, a DO value above 0.50 mg/L in the anammox reactors would usually inhibit the activity of anammox bacteria.Great efforts have been devoted to seek a strategy to fast the start-up of anammox, mainly focusing on (1) applying suitable reactors to reduce the loss of sludge, (2) controlling the optimum operational conditions to promote the proliferation of anammox bacteria and (3) inoculating appropriate seed sludge to improve the quality of sludge. However the time, which was necessary for the start-up of anammox process, was still much longer than that of traditional nitrification-denitrification process.Therefore, basing on the perspectives of minimizing the sludge loss and maximizing the cultivation conditions, this research aimed to indicate the optimum start-up method and operation control of anammox process, which was necessary for widely application as supports and references. One aspect, ZVI enhanced reactor was set up by adding zero-valent iron in UASB to provide a more appropriate condition. Another aspect, novel non-woven MBR was set up to minimize the sludge washout and realizebiomass retainment. Aimed to slove the problems of sludge washout and low total nitrogen removal simultaneously, novel ZVI assembled reactors of which top is polyester sponge and bottom is sponge iron were also employed. The main research results are as follows.(1) The addition of ZVI could shorten the start-up time of anammox process, especially the reactor with ZVI, could complete the start-up in 84 days, shortening about 33.4%. The addition of ZVI, especially nZVI, could promote the secretion of extracellular polymeric substances (EPS) in anammox stage. With mZVI and nZVI, the secretion of EPS reached to 142.8 and 149.3 mg/g VSS on day 150. Adding ZVI also could accelerate the proliferation of anammox bacteria. The abundance of anammox cells in control reached 1.82×107 copies/ml, while the copy numbers in reactors with mZVI and nZVI were about one order of magnitude upper, reaching 1.09×108 and 1.44×108 respectively.(2) Adoption of MBRs could reduce the loss of biomass significantly. During the operation time, the effluent SS of tMBR was less than 15 mg/L, while that in nMBR was less than 35 mg/L. However, the effluent SS in nMBR could reach 7 mg/L after the formation of biofilm. The tMBR could accomplish anammox process in 56 days with unstable nitrogen removal performance, while nMBR could accomplish the start-up of anammox in 44 days, and obtain a nitrogen removal rate of 245.4 mg N/L/d with a shortened HRT. Employing nMBR also could enhance the formation of biofilm with little suspended sludge in comparison with tMBR.(3) Adoption of this novel ZVI assembled reactor could accomplish the recovery of anammox bacteria in 16 days under the low nitrogen loading rate. Employing this novel UASB, especially the R1 with sponge iron, could resist the influence of low temperature and mutational nitrogen loading rate. The nitrogen removal rate could reach 1100 mg N/L/d in R1.In conclusion, this paper would provide new way and solution to solve the nitrogen pollution in Chinese aqueous environment, as well as offering theoretical reference and technological support to the wide application of anammox process.