| During the process of sanitary landfill treatment of domestic waste, it will produce leachate, which has complex composition and extremely high content of nitrogen. Especially the mature leachate landfill, in which organic matter is decomposed and C/N becomes imbalance, making it hard to remove nitrogen by traditional nitrification-denitrification. Anaerobic ammonia oxidation (Anammox) is a new means for nitrogen removal with no carbon source, and there exists certain complementarity with denitrification, which make it possible for the coordination for Anammox and denitrification during leachate treatment. However, the effect of leachate quality conditions, such as organic load and different nitrogen forms, etc., to Anammox and denitrification is unknown. In addition, how to start anaerobic ammonia oxidation process quickly and keep it operating stably is also should be researched, which has practical meaning for actual leachate treatment.In this research, aged refuse from a landfill in Shanghai was adopted as filler to build landfill bioreactors. Then we explored the effect of leachate quality, such as organic load, BOD/TN and NO2-/NH4+, to Anammox and denitrification in nitrogen removal through orthogonal test. By selecting the suitable inoculation sludge source, we researched the effective strategies to start landfill bioreactors quickly. In addition, the efficiency and contributions rate of Anammox and denitrification were detected by 15N isotope tracer technique. The conclusions were shown as follows:(Ⅰ) Affects of landfill leachate characteristicsWithin the parameters of this study, we found:(ⅰ) In the 9 reactors in this research, leachate quality of organic load, BOD/TN and NO2-/NH4+ inthe reactor with optimal removal effect were 0.04 kg/(m3·d),0.20and 1.5, of which total nitrogen and ammonia nitrogen removal rates were 92.66% and 81.67%, respectively. And leachate quality of organic load, BOD/TN and NO2-/NH4+ inthe reactor with poor removal effect were 0.02 kg/(m3·d),0.05 and 0.5, of which total nitrogen and ammonia nitrogen removal rates were only 43.82% and 41.80%.(ii) Organic load, BOD/TN ratio were positively related with bioreactor effect, which showed that the increase of organic load and BOD/TN ratio is beneficial for the effect of leachate. When NO2-/NH4+ ratio were 0.5 or 1.5, it showed poor correlation with reactor effect. But when NO2-/NH4+ ratio was 1.0, the correlation is high, which means 1.0 was the suitable NO2-/NH4+ rate for this study.(iii) According to the results we got, the optimal leachate quality was suggested during nitrogen removal process, of which organic load, BOD/TN and NO2-/NH4+ ratio was 0.04～0.07 kg/(m3, d),0.20 and 1.0, respectively.(II) Strategy for bioreactor quick launchResults showed:(i) Using the aged refuse as filler, which mixed with anaerobic activated sludge and the rate was 6%, could improve the effect of reactors quickly. During the early stage, the total nitrogen and ammonia nitrogen removal rate in the experimental group were significantly higher than that of control group. And it was earlier for the experimental group to reach a stable state, reduced about 42.86%, which means it could shorten the time of the reactor domestication and speed up the reactor startup. In other words, adding the anaerobic activated sludge into reactor was an effective strategy to realize the acceleration of reactor operation. (ii)Compared with the experimental group, while total nitrogen and ammonia nitrogen removal rate of control group could maintain the same level as experimental group, but it needed more time to reach the stable state.(III) Mechanism of denitrification and Anammox for nitrogen removalBy using 15N isotope tracer technology, the contributions of denitrification and Anammox during nitrogen removal were researched. Results showed:(i) The contribution rates of Anammox were in this study was 7.50%～26.95%. (ii) In the same reactor, contribution rates of Anammox in the lower parts (about 11.02%～26.95%)were significantly higher than the upper (approximately 7.5%～11.86%).It meant that the condition of lower parts in reactors were more suitable for Anammox to remove the nitrogen. (iii) Adding the anaerobic activated sludge used in this research could significantly increase the denitrification efficiency, but it would reduce the contribution of Anammox. (iv) The contribution rate of Anammox is closely related to NO2-/NH4+ rate, with the correlation coefficients of 0.997. The growth rates of Anammox contribution with NO2-/NH4+ of 1.5 were significantly higher than that of 0.5 or 1.5, which showed that the suitable rate of NO2-/NH4+ effect the growth of Anammox contribution.To sum up, the leachate quality had important effect on nitrogen removal of the landfill bioreactors. Anammox could cooperate with denitrification to remove nitrogen, and the highest contribution rate of Anammox could reach 27%.In addition, though the inoculation of anaerobic activated sludge, the acceleration of reactor operation could be realized. |
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