Abstract
Plants can remove pollutants through direct absorption and by providing habitats for microbes to stimulate their activities. The aboveground plant biomass is usually harvested to remove pollutants absorbed in plant tissues. However, the effect of plant harvesting during summer on the performance of constructed wetlands and microbial abundance is unclear. In this study, three types of microcosms were set up, including: cleared group (both shoots and roots were harvested), harvested group (only shoots were harvested) and unharvested group. The concentrations of ammonia nitrogen and chemical oxygen demand in the effluent of the harvested group were the lowest. The nitrogen mass balance showed that summer harvesting improved nitrogen absorbance by plants, which was 1.24-times higher than that in the unharvested group. Interestingly, the other losses were taken up by the highest amounts in the cleared group, which were 1.66- and 3.72-times higher than in the unharvested and harvested group, respectively. Quantitative polymerase chain reaction revealed that harvesting of shoots during summer increased the microbial abundance. Additionally, Proteobacteria was the dominant phylum among all bacteria according to pyrosequencing analysis. These results indicate that harvesting of shoots during summer has positive effects on pollutant removal and microbial abundance.
Highlights
Constructed wetlands (CWs) have been widely used for wastewater and heavy metal treatment [1]due to their low cost and energy consumption [2]
Found that harvesting in late autumn had a negative effect on chemical oxygen demand (COD) and ammonia nitrogen (NH4 + -N) removal with lower plant radial oxygen loss, microbial abundance and activity
Summer harvesting showed a positive effect on COD and NH4 + -N removal, and there is a positive correlation between the removal efficiency of pollutants and dissolved oxygen oxygen (DO) concentrations in effluent (r2 > 0.635)
Summary
Constructed wetlands (CWs) have been widely used for wastewater and heavy metal treatment [1]. Wang et al [5] found that harvesting in late autumn decreased the oxygen release rate in CWs and showed a negative effect on pollutant removal. Summer harvesting may postpone subsequent plant growth and affect plants radial oxygen loss (ROL) and nutrient transfer from stems to rhizomes [5,10]. Found that harvesting in late autumn had a negative effect on chemical oxygen demand (COD) and ammonia nitrogen (NH4 + -N) removal with lower plant radial oxygen loss, microbial abundance and activity. Microbes play the main role in pollutant removal, and plants could enhance microbial activity and abundance by providing oxygen and a carbon source from root-system [12].
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