| With the increase of urbanization and people's living standards in China,the number of domestic garbage has increased significantly.The main treatment method of domestic garbage in China is landfill.During the process of stacking and landfilling,pollutants contained in the garbage leach out with water to generate landfill leachate under the action of fermentation and soaking of rainwater and surface water.Landfill leachate is characterized by its complex composition,including a large amount of refractory organics,high concentrations of ammonia nitrogen,heavy metals,and other toxic substances.Failure to effectively treat landfill leachate can cause serious environmental damage.Therefore,the development of a process for the efficient treatment of landfill leachate is of great importance to the protection of the environment.For large amounts of organics in landfill leachate,this study proposed multi-stage biological contact oxidation processes.During the operation of the reactor,the COD and ammonia nitrogen removal were examined and analyzed.During the start-up period,a mixture of glucose and landfill leachate with a COD concentration of 2000 mg/L was used to acclimate bacteria,and the adaptability of the bacteria to landfill leachate was gradually improved by continuously increasing the proportion of landfill leachate.With the increase of landfill leachate,the COD removal rate showed a steady decline from 90.74%to 80.1%.After acclimation and stable operation,the system was highly adaptable.The COD concentration in the process from 2000 mg/L to 5000 mg/L was always stable at over 80%.In order to investigate the optimum process parameters of the multi-stage biological contact oxidation method,response surface analysis was performed in the system and the optimal parameters were as follows:influent COD concentration 4000 mg/L,aeration volume 9 L/min,temperature 35?,HRT 24h.Under this condition,the COD removal rate reached 91.28%,which ensured both the removal rate and the processing rate.It could be seen that the process parameters had a significant impact on the processing efficiency of this method.In order to deal with the ammonia nitrogen in the effluent of multi-stage contact oxidation,this study proposed that the effluent was regarded as wastewater containing a certain amount of hard-degradable organic matter and high-concentration ammonia nitrogen,and treated by single-stage autotrophic nitrogen removal using anammox and nitrification.In this study,artificially simulated wastewater was used to simulate the ammonia nitrogen in the effluent of multi-stage biological contact oxidation with ammonium sulfate,and the remaining refractory COD was simulated with humic acid and biooxidized humic acid,respectively,to explore the effect of COD on ammonia nitrogen removal.Firstly,this study discussed the removal of ammonia nitrogen when using humic acid as a COD source.When the nitrogen removal rate of ammonia nitrogen was over 1 kgN/m3/d,and the influent concentration of ammonia nitrogen was about 700 mg/L,humic acid began to be added,when the removal rate of ammonia nitrogen was about 84.3%.The experimental results showed that humic acid could promote the removal of ammonia nitrogen in the SNAP reactor.Under the condition of influent ammonia nitrogen of 800 mg/L,when the COD concentration reached 200 mg/L,the removal rate of ammonia nitrogen exceeded 90%;the COD concentration reached 550 mg/L,the ammonia nitrogen removal capacity reached its maximum,and the removal rate was stable at about 98%;when COD concentration exceeded 700 mg/L,the ammonia nitrogen removal capacity gradually decreased,but even if the COD concentration reached 1500 mg/L,the removal rate of ammonia nitrogen also exceeded 90%.This discovery provided a reference for the improvement of the biological activity of anammox bacteria.Secondly,when biooxidized humic acid was used as the COD source,the nitrogen removal ability of the reactor was not significantly reduced as influent COD increases from 0 to 500 mg/L,but the system became very stable.This discovery laid the foundation for multi-stage biological contact oxidation and SNAP technology to treat landfill leachate.Through high-throughput sequencing,the bacteria community structures of multi-stage contact oxidation reactors and SNAP reactors were analyzed.The dominant genus of the multi-stage contact oxidation reactor was the non-culturable spirochetes and the unclassified Connexa.According to the analysis,the impact of COD concentration on the bacteria community was greater than that of COD type.The COD changed from 0 to 2000 mg/L,from 2000 mg/L to 5000 mg/L and from 2000 mg/L mixed liquor to 2000 mg/L landfill leachate,respectively.Compared with landfill leachate,the proportion of each species changed greatly,and the community structure had undergone significant changes.For the SNAP reactor,humic acid had little effect on the overall bacterial population abundance and diversity,but it had an impact on the activity of each strain,almost all the proportion of bacteria changed,especially the larger bacteria.Through analysis,it could be confirmed that a certain concentration of humic acid played a significant role in promoting the enrichment of anammox bacteria in the SNAP system,and the dramatic increased in systemic denitrification capacity was closely related to changes in anaerobic ammonia-oxidizing colonies.The biological oxidation of humic acid had almost no effect on the colony of the SNAP system.Based on the above findings,this study proposed a method for efficient treatment of landfill leachate:a multi-stage biological contact oxidation process was used to treat the leachate,and SNAP was used to treat its effluent.At the same time,a potential method of promoting the culture of anammox bacteria was also found. |
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