| Nitrogen pollution in aquatic bodies, which is considered as one of the main causes to the water quality deterioration and biodiversity shrinkage, has become an increasingly serious environmental issue and has been addressed worldwide. Compared to the conventional biological nitrogen removal process, anaerobic ammonium oxidation (Anammox) is more promising due to its advantages of absence of additional carbon source and avoiding secondary pollution as well as saving energy. However, in an attempt to put Anammox into practical engineering application, many problems still remain unsolved, i.e., the instability issue caused by influent loading shock and the nitrate production in the Anammox-treated effluent as well as the long start-up length for large-scale reactor. In order to pay the way for applying Anammox process to practical application, therefore, our work aims to explore the solutions to the abovementioned critical issues.The influence of nitrogen loading and instant high-temperature shock on Anammox process was investigated in a 3.2 L up-flow anaerobic sludge blanket (UASB) reactor. It was shown that nitrogen loading shock has noticeable impact on nitrogen removal efficiency. Up to 99.8% of NH4+-N and NO2--N removal were both achieved when nitrogen loading rate is 0.136~0.142 kg TN·(m3·d)-1. Both NH4+-N and NO2--N removal efficiencies decreased when nitrogen loading rate is raised slightly to 0.136~0.142 kg TN·(m3·d)-1, with 92% removal of ammonia and 95% of nitrite. Although the nitrogen removal efficiencies declined substantially to 72.8% when nitrogen loading rate is raised to 0.255~0.280 kg TN·(m3·d)-1, the reactor can still work steadily. The TN removal efficiency increased to 85% when nitrogen loading rate is decreased to 0.099~0.111 kg TN·(m3·d)-1. However, an obvious impact was observed when an instant high-temperature shock occurred, the nitrogen removal performance improved rapidly and reached to a steady state, indicating that this UASB-Anammox reactor has strong shock resistance ability.In order to solve the issue of nitrate production in the Anammox-treated effluent and to apply Anammox to treat the organic wastewater, the feasibility of combining Anammox and denitrification in single reactor was investigated. By continuously adding organic matter, the Anammox-Denitrification reactor was successfully started-up within 35 days in conditions of an organic loading to total nitrogen (TN) ratio of 1 and the influent nitrogen loading rate at 0.26 kg·m-3·d-1. During the stable phase, the removal efficiencies of ammonia, nitrite, TN and COD were found high up to 95.3%, 99.1%, 94.0% and 93.2%, respectively; the average ratio of removed ammonia, removed nitrite and generated nitrate was 1﹕1.32﹕0.03, Effluent alkalinity and pH value were slightly higher than influent alkalinity. The synergism between Anammox and denitrification could reduce the nitrogen production, it is of importance to improve the quality of the effluent from the Anammox reactor, and it is also essential for treating the nitrogenous organic wastewater. On the basis of the stoichiometry, the ratio of the removed ammonia to the removed nitrite in the Anammox process is 1︰0.77. Equilibrium of the competition of electron donor between Anammox and denitrification was obtained by the inhibition mode of metabolism mechanism for the Anammox organisms. To achieve an efficient nitrogen removal performance by using the synergism between Anammox and denitrification, the ratio of organic COD to ammonia should not be less than 1.0. The inhibition mode of metabolism mechanism coupled with the completation of metabolic product from Anammox and denitrification were proved to be the two prerequisites for synergistic nitrogen removal. Further study was needed due to the complexity of the mechanism on the synergism between Anammox and denitrification. The effect of organic loading shock on the Anammox-Denitrification reactor was also investigated. Results obtained indicated that the Anammox- Denitrification reactor has strong organic loading-resistance ability.Scaling-up strategy was used to start-up a new Anammox reactor. Sludge obtained from a sequencing batch reactor (SBR) treating landfill leachate and a small amount of Anammox sludge from another Anammox reactor were mixed and then seeded into an anaerobic sequencing batch reactor (ASBR) with a working volume of 50 L. The Anammox sludge constituted 3.2% of the total seeded sludge. The ammonia and nitrite removal efficiencies was found high up to 95.58% and 99.29% by the 46th day, respectively, indicating that Anammox has become the dominant reaction in the reactor. As a result, this scaling up strategy could accelerate the start-up of Anammox reactor.
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