Study On Effects Of Pure Oxygen Aeration On The Performance Of Landfill Leachate A/O Treatment System And Its Microbial Community Structure

At present,most of the leachate treatment use the conventional activated sludge process,which has achieved good performances.However,there still exist some problems such as low oxygen utilization and large odor.Previous studies found that pure oxygen aeration activated sludge has the advantages of improving sludge activity,increasing dissolved oxygen,reducing odor and energy consumption.Pure oxygen aeration system has been widely applied in the treatment of domestic sewage and industrial wastewater and achieved good results.However,so far,it is rarely used in the waste incineration industry fresh leachate treatment process,which needs further research and improvement.Therefore,we conducted an experience to study effects of pure oxygen aeration on the performance of A/O leachate treatment process in the incineration plant leachate treatment station in Jiangsu,Changzhou,meanwhile,explore the influence on activated sludge microbial community structure and diversity.We also isolated a high efficient aerobic denitrifying bacterium from the functional bacteria in the avtivated sludge.In this paper,COD and NH₃-N were used as indicators to investigate the effect of pure oxygen aeration on the performance of A/O process.The results showed that pure oxygen aeration improved the sludge activity,and the average removal rate of COD and NH₃-N reached 87.20%and 98.30%respectively.Moerover,under the condition that the water quality of the leachate was unstable,the system showed a good ability to resist load impact,which indicated that pure oxygen aetation had a certain effect on maintaining the stable of the system.Then,by comparing the effluent quality of pure oxygen aetation tank and air aetation tank,the removal rate of COD and NH₃-N of pure oxygen aetation tank is higher than that of air aetation tank,and the pure oxygen aetation has higher volume load.In addition,we compared the operation costs of pure oxygen aeration and air aeration and the results showed that both are equivalent in operation costs considering the annual treatment capacity.Moreover,by comparing the microbial community structure and diversity of activated sludge in pure oxygen aeration tank and air aeration tank,we found that the microbial community structure in pure aeration tank was more rich and diverse than air aeration tank.Among them,the most dominant bacteria in pure oxygen aeration tank was phylum Proteobacteria.The most dominant bacteria in air aeration tank was phylum Bacteroidetes.In addition,the nitrifying bacteria community structure in the pure aeration aeration tank was more abundant than that in the air aeration tank.Meanwhile,the denitrifying bacteria diversity is also higher than that in the air aeration tank,and a large amount of aerobic denitrifying bacteria were found in both pure oxygen aeration tank and air aeration tank.Then,we obtained the activated sludge from the above pure oxygen aeration tank.Using BTB as indicator,an efficient aerobic denitrifying bacterium was screened by using the dilution coating plate method.The morphological,physiological and biochemical characteristics of the strain wer preliminaraily identified,combined with the 16S rDNA gene sequence analysis,the strain was identified as Bacillus cereus,named Bacillus cereus CZ1.And the strain CZ1 of aerobic denitrification and heterotrophic nitrification ability were determined.The results showed that the removal rate reached 97.69%of the NO₃^--N in 24h,and no NO₂^--N accumulation,indicating that the strain had good aerobic denitrification ability.The NH₄⁺-N removal rate within 48h reached 98.15%in the medium with NH₄Cl as the sole nitrogen source,and only a slight accumulation with NO₃^--N occurred in the whole reaction process.Moreover,NO₂^--N was not detected at all.Meanwhile,the effects of environmental factors such as carbon source,temperature and initial pH on the denitrification were investigated.The optimal aerobic denitrification conditions were as follows:temperature of 35℃,sodium succinate as sole carbon source,C/N ratio of 6,initial pH of 7.0⁷.5,rotating speed of160r/min.Futhermore,the denitrification efficiency of the strain was always higher than 90%at 60-200r/min,indicating that the strain had high oxygen-resistant range.