Researches On The Biological Denitrification Process By Anoxic/Aerobic Membrane Bioreactor

A/O-MBR biological denitrification process is a new combination type of watertreatment process. Compared with the traditional biological denitrification technology,due to the efficient intercept feature of MBR, generation cycle longer nitrifyingbacteria to get trapped in membrane bioreactor and enrichment. So it has a morecomplete nitration reaction and a better denitrification effect. This subject based onthe principle of treating ammonia nitrogen containing heavy metal chemicalwastewater in Zhuzhou, and researched on the biological denitrification process ofA/O-MBR. Research conclusions have a important guiding significance for the actualproject operation, and also play a positive and promoting role to protect the waterenvironment and water balance of xiangjiang river.First of all, research on the start of A/O-MBR system. The results show that formbasically no nitrification to have significant nitrification need a process, this processlasts for more than a week at least. In the process of the operation of A/O-MBR, youcan observe the changes of pH in the aeration tank to determine the presence anddegree of nitration reaction. Further, by observing the ratio of sludge settling, thesupernatant absorbance, the changes of the concentration of dissolved oxygen in theaeration tank, as well as the sludge flocs observation, in a certain extent, reflect thebiological activity of the sludge in the reactor, and then to determine the effect ofaerobic microbial on the degradation of organic pollutants.Then focuses on researching the running characteristics of A/O-MBR biologicaldenitrification process. The results show that A/O-MBR process has a very goodremoval efficiency of organic matter. Membrane for removal of organic pollutants hascertain contribution, but the biodegradation rate is higher than the membrane in theremoval rate of COD. A/O-MBR process has a high removal rate of ammonianitrogen, the maximum value of99.8%, and in most of the time the water stablebelow1mg/L. Interception of membrane on the removal rate of ammonia nitrogencontributes little, but it can strengthen the nitration reaction in the system, so as toimprove the removal rate of ammonia nitrogen. A/O-MBR process for total nitrogenremoval also can be obtained very good effect, the average total nitrogen removal ratewas about68%. Through experimental analysis, determine the optimum operating parameters of the A/O-MBR process: aeration tank DO is2.5³.5mg/L, anoxic poolDO is0⁰.5mg/L, MLSS is2300²800mg/L, C/N is6.0⁶.7, the IR is300%.The third stage investigated the effects of heavy metal to the A/O-MBR processoperation. The results show that with the increase of metal concentrations, theremoval rate of COD, NH₄⁺-N, TN all showed a trend of decline. Studies also havefound that four kinds of heavy metal toxicity is different for different kinds ofmicroorganisms. The size order of heavy metal toxicity to aerobic heterotrophicmicroorganisms is: composite metal＞Cd²⁺＞Zn²⁺＞Fe³⁺＞Mn²⁺. The size order ofheavy metal toxicity to denitrification bacteria is: composite metal＞Zn²⁺＞Cd²⁺＞Fe³⁺＞Mn²⁺. Heavy metal has a strengthening and promoting effect on membranefouling. When handing the actual wastewater containing heavy metal, transmembranepressure increases rapidly, the backwashing effect is not obvious and rebound soon.Analysis of the reason is that a large number of massive scale metal material attachedto the surface of membrane, resulting in clogging of the membrane.Finally, through reasonable assumptions, established the dynamics model ofpollutants removal by biological denitrification process of A/O-MBR. The dynamicsmodel of COD removal is C_e=C₀/（0.001343*θ_pX_p-1）, The dynamics model ofNH₄⁺-N removal is N_e²+[15.01*V_pθ_p+10^0.051T-1.158-N₀]·N_e-10^0.051T-1.158N₀=0, The dynamics model of TN removal is n_e=（（1+R）n_A+0.007397X_Aθ_A-n₀）/R.