Research Of Key Technologies And Their Mechanisms Of Anaerobic Ammonia Oxidation

Anaerobic ammonia oxidation (Anammox) process is a new type of biotechnology for nitrogen removal with high efficiency and low cost, which has a very good application prospect and high commercial value. But Anammox bacteria are chemoautotroph with long double time and low yield rate. Besides, they are sensitive to changes of environmental conditions. The large-scale application of Anammox process is often limited by the seeding Anammox sludge, substrates and exogenous toxicants (i.e. antibiotics). Therefore, some key technologies and their mechanisms are investigated to solve these problems. The main results are as follows:1) The start-up characteristics and sludge characteristics were revealed, and a method to solve the shortage of seeding sludge and a method to monitor the specific Anammox activity were established.It was proved that anaerobic methanogenic sludge (AMS), fresh Anammox sludge (FAS) and stored Anammox sludge (SAS) could be used to start up Anammox-EGSB bioreactors successfully (the reactors were named Rl, R2and R3, respectively). But the start-up progresses showed different characteristics. The start-up course of R1could be divided into three phases including autolysis phase (15d), lag phase (54d) and activity elevation phase (40d). The start-up courses of R2and R3only included lag phase (2d and12d, respectively) and activity elevation phase (15d and57d, respectively). The performance of R3was better than that of R1, but worse than that of R2. The physical parameters color value a*, particle diameters and settling velocities were raised. The chemical parameters extracellular polymeric substances (EPS) and heme contents are elevated. Besides, the biological parameters dehydrogenase activity (DHA) and specific Anammox activity (SAA) were also promoted. The color value a*, heme contents, DHA and SAA were closely related to each other. Under the condition without supply of Anammox sludge, AMS could be used as the seeding sludge for Anammox process. Bathing the Anammox sludge in the effluent of bioreactors was a convenient way to keep the activity of Anammox sludge. Seeding Anammox reactor with SAS was effective way to shorten the start-up time. Color value a*, heme content or DHA could serve as the parameters to monitor the SAA of Anammox sludge, whose measurements were more convenient than the batch test. Among them, color value a*was the simplest and most environmental friendly.2) The influence of two substrates on Anammox reaction and sludge characteristics was studied and the inhibition mechanism of endogenous toxicants was explored.The batch tests showed that the half inhibition concentrations (IC50) and their95%confidence interval of ammonia and nitrite were1670(1516.7～1820.0) mgN·L-1and585.6(241.1～912.1) mgN·L-1. Nitrite was more toxic than ammonia. The joint action of ammonia and nitrite was independent. The continuous cultivation tests showed that the performances of reactor Al, A2and A3were steady, which meant ammonia did not inhibit Anammox reaction under the setting ammonia concentrations. However, the performances of reactors B1, B2and B3were sharply down, which meant nitrite inhibited Anammox reaction under the setting nitrite concentrations. The physical, chemical and biological parameters of the sludge in A1, A2and A3did not have significant changes while the situation was totally different in B1, B2and B3. All the parameters declined sharply. All the changes of sludge characteristics were in accordance with the reactors’performances. The inhibition mechanism of nitrite is as follows:the excessive nitrite inhibited the activity of key enzyme hydrazine dehydrogenase (HDH), which led to the disturbance on substrate catabolism. On the other hand, the accumulated intermediate hydrazine (N2H4) could poison the Anammox cell.3) The influence of exogenous toxicants (four antibiotics) on Anammox performance and sludge characteristics was studied and the inhibition mechanisms of exogenous toxicants were explored.The batch tests showed that the half inhibition concentrations (IC50) and their95%confidence interval of penicillin G-Na, polymyxin B sulfate, chloramphenicol and kanamycin sulfate were2215.8(1972.2-2611.1)mg·L-1、39.1(35.7-42.4) mg·L-1441.2(431.8-445.5) mg·L-1and1188.6(1022.7-1318.1) mg·L-1. The antibiotics toxicities were as follows:polymyxin B sulfate> chloramphenicol> kanamycin sulfate> penicillin G-Na. The joint actions of antibiotics or the joint actions of substrates and antibiotics mostly belonged to additive effect. Only small part of treatment groups belonged to synergistic effect or independent effect. The continuous cultivation tests showed that the performances of reactors with different antibiotics dosage declined with the increase of antibiotics’concentrations. All the changes of sludge characteristics were in accordance with the reactors’performances. The inhibition concentrations got from continuous cultivation tests were much lower than those from batch tests. Under the exogenous toxicant stress, Anammox bacteria might produce much more EPS, especially extracellular protein to form the barrier to prevent the cell from the toxicants. This was similar to the self-protection mechanism of other bacteria.4)In order to solve the nitrogen pollution from strong-ammonium pharmaceutical wastewater, a full-scale short-cut nitrification process combined with Anammox process was investigated. The results showed that the short-cut nitrification process and Anammox process could successfully remove nitrogen from pharmaceutical wastewater. In the combined system, influent ammonia and effluent ammonia were (430.40±55.43) mg-L-1and (24.26±11.37) mgL-1, respectively. Ammonia removal efficiency was (81.75±9.10)%. Volumetric nitrogen loading rate and volumetric nitrogen removal rate of Anammox process were (4.31±1.07) kgN·m-3·d-1and (3.66±0.96) kgN·m-3·d-1, respectively. Two-step mode using synthetic wastewater and real wastewater was suitable for operations of the short-cut nitrification system which provided substrates for Anammox system. The start-up took about74d. Nitrite accumulation efficiency was (52.11±9.13)%. Maximum volumetric nitrogen loading rate and volumetric nitrogen removal rate were0.26kgN·m-3·d-1and0.15kgN·m-3·d-1, respectively. The combination of Anammox sludge growth with sequential biocatalyst addition was suitable for the operation of Anammox process. The start-up process took about145d. Maximum volumetric nitrogen loading rate and volumetric nitrogen removal rate were6.96kgN·m-3·d-1and6.35kgN·m-3·d-1, which were in the leading level in full-scale reactors.