Abstract
Dynamics of bacterial community abundance and structure of a newly established horizontal subsurface flow (HSSF) pilot-scale wetland were studied using high-throughput sequencing and quantitative polymerase chain reaction (PCR) methods. Bacterial community abundance increased rapidly within one month and stabilised thereafter in three replicate HSSF constructed wetland (CW) mesocosms. The most dominant phylum was Proteobacteria, followed by Bacteroidetes in wetland media biofilms and Firmicutes in influent wastewater. CW bacterial community diversity increased over time and was positively related to the wastewater treatment efficiency. Increase in the abundance of total bacteria in the community was accompanied with the abundance of denitrifying bacteria that promoted nitrate and nitrite removal from the wastewater. During the 150-day study period, similar patterns of bacterial community successions were observed in replicate HSSF CW mesocosms. The data indicate that successions in the bacterial community in HSSF CW are shaped by biotic interactions, with a significant contribution made by external abiotic factors such as influent chemical parameters. Network analysis of the bacterial community revealed that organic matter and nitrogen removal in HSSF CW could be, in large part, allocated to a small subset of tightly interconnected bacterial species. The diversity of bacterial community and abundance of denitrifiers were good predictors of the removal efficiency of ammonia, nitrate and total organic C in HSSF CW mesocosms, while the removal of the seven-day biochemical oxygen demand (BOD7) was best predicted by the abundance of a small set of bacterial phylotypes. The results suggest that nitrogen removal in HSSF CW consist of two main pathways. The first is heterotrophic nitrification, which is coupled with aerobic denitrification and mediated by mixotrophic nitrite-oxidizers. The second pathway is anaerobic denitrification, which leads to gaseous intermediates and loss of nitrogen as N2.
Highlights
Constructed wetlands (CWs), known as treatment wetlands, are engineered systems designed to utilise the natural processes of biological wetlands to remove pollutants from wastewater [1,2].Over the last decade, constructed wetland (CW) have become widely used for wastewater treatment as they represent a cost-effective, ecologically-friendly, and simple alternative to conventional technologies for wastewater purification [3,4,5]
The results show that the bacterial community in Horizontal subsurface flow (HSSF) CW can be described as a complex adaptive system, in which exogenous factors impact the endogenous dynamics of the community
The results of this study show that the abundance of HSSF wetland media biofilm system (WMB) bacterial community reached a maximum after two months of system operation and remained stable despite the drop in temperature of the system
Summary
Constructed wetlands (CWs), known as treatment wetlands, are engineered systems designed to utilise the natural processes of biological wetlands to remove pollutants from wastewater [1,2].Over the last decade, CWs have become widely used for wastewater treatment as they represent a cost-effective, ecologically-friendly, and simple alternative to conventional technologies for wastewater purification [3,4,5]. Constructed wetlands (CWs), known as treatment wetlands, are engineered systems designed to utilise the natural processes of biological wetlands to remove pollutants from wastewater [1,2]. There is the increasing trend of using HSSF CW for other types of wastewater including industrial, agricultural, and landfill leachates [6,7,8,9]. While the removal mechanisms of physical and chemical pollutants in CWs are well known [10], the understanding of microbial processes related to pollutant removal is still insufficient [11].
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