| Rural swine wastewater?SW?contains high concentrations of pollutants,including suspended solids,organic material,and nutrients?i.e.,nitrogen and phosphorus?with large discharge volume,which must be treated prior to its discharge into water bodies.SW will cause increasingly serious environmental problems and serious harm to human health without proper treatment.Compared with conventional sewage treatment processes,constructed wetlands?CWs?have the advantages of easy construction,low operating costs,low energy consumption,high processing efficiency,and convenient maintenance and management.As one of the main types of CWs,the surface-flow constructed wetlands?SFCWs?are usually used for SW treatment in large-scale pig farms and rural decentralized swine breeders due to their obvious characteristics of simple structure,low infrastructure cost,not easy to be plugged and the relatively abundant rural land resources.Microorganisms undertake the task of degrading pollutants in water.It is the main mechanism of pollutant removal and plays an indispensable role in CW systems.However,little is known about the spatiotemporal change patterns of microbial communities and their response to environmental factors in SFCWs.The research is of great significance to construct and optimize more efficient wastewater treatment CWs and carry out comprehensive environmental management.Nitrogen is one of the dominant pollutant in SW and the removal of nitrogen is one of the key issues in the design of CWs for SW treatment.It is particularly important to study the functional microbials associated with the nitrogen removal processes.So far,nitrification-denitrification and anaerobic ammonia oxidation?anammox?are two important microbial nitrogen removal pathways.Most studies have focused on nitrification-denitrification and their associated microorganisms in SFCWs for treating SW.However,whether anammox bacteria are widely present and their nitrogen removal contribution in CW systems are not fully understood yet,which need in-depth analysis and evaluation.By studying the abundance,community structure and activity of anammox bacteria with the change of environmental conditions as well as its driving effect of anammox process in the high-nitrogen SW CW treatment systems,it is helpful to increase the understanding of nitrogen-removing microbial driving mechanism in CWs.Moreover,it will provide scientific basis for follow-up studies to optimize and regulate microbial nitrogen transformation processes in CWs to increase the removal rate and reduce N2O emissions.The application and promotion of CWs technology in rural SW treatment has a very positive significance.Therefore,in this study,based on the long-term positioning pilot-plant-scale CW system for treating SW of varying strengths,we studied the spatiotemporal changes of microbial community diversity and the ecological characteristics of anammox bacteria and their nitrogen-removing contributions in SFCWs.Firstly,we studied the spatiotemporal variation of the microbial?bacteria and archaea?diversity and composition in SFCWs under different strength of SW treatment.Based on Illumia Miseq high-throughput sequencing technique,we systematicly analyze and compare the microbial community diversity and composition and the relationship between sediments physicochemical factors and microbial community diversity in SFCW systems.Our results revealed that highly diverse prokaryotic communities were present in the SFCWs,with Proteobacteria?16.44–44.44%?,Acidobacteria?3.25–24.40%?,and Chloroflexi?5.77–14.43%?being the major phyla,and Nitrospira?4.14–12.02%?,the most dominant genus.The microbial communities in the sediments varied greatly with location and season,which markedly altered the microenvironmental conditions.Principal co-ordinates analysis indicated that SW strength significantly influenced the community structure in sediments of the SFCWs,and canonical correspondence analysis illustrated that the shifts in microbial communities were strongly related to NO3--N and TN in winter;and in summer with NH4+-N,NO3--N,NO2--N,TN,TP,SOM,and pH.In conclusion,the use of high-throughput sequencing greatly enhanced our understanding of microbial communities with different functional groups in SFCWs.Secondly,we mainly investigated the ecological characteristics and distribution of anammox bacteria and nitrogen-removing effect and mechanism on wastewater associated with sediments from SFCWs treating SW of varying strengthsto analyze the diversity,activity,and role of anammox bacteria in sediments of SFCWs.We found that anammox bacteria were abundant in SFCW sediments,as indicated by 7.5×105 to 3.5×106 copies of the marker hzs B gene per gram of dry soil.Based on stable isotope tracing,potential anammox rates ranged from 1.03 to 12.5 nmol N g-1dry soil h-1,accounting for 8.63-57.1%of total N2 production.We estimated that a total N removal rate of 0.83-2.68 kg N year-1 was linked to the anammox process,representing ca.10%of the N load.Phylogenetic analyses of 16S ribosomal RNA?rRNA?revealed the presence of multiple co-occurring anammox genera,including“Candidatus Brocadia”as the most common one,“Ca.Kuenenia,”“Ca.Scalindua,”and four novel unidentified clusters.Correlation analyses suggested that the activity and abundance of anammox bacteria were strongly related to sediments pH,NH4+-N,and NO2--N.In conclusion,our results confirmed the presence of diverse anammox bacteria and indicated that the anammox process could serve as a promising N removal pathway in the treatment of swine wastewater by SFCWs. |
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