Abstract
To identify the facilitation effect of a cool-season aquatic macrophyte (FEam) for use in effluent purification via constructed floating wetlands (CFWs) and to determine the possible pathways used during a winter period with an average temperature of less than 5 °C, pilot-scale CFWs were planted with the cold-season macrophyte Oenanthe clecumbens and were operated as batch systems. Although some leaves withered, the roots retained relatively high levels of activity during the winter, which had average air and water temperatures of 3.63 and 5.04 °C, respectively. The N and P removal efficiencies in CFWs decreased significantly in winter relative to those in late autumn. The presence of cool-season plants resulted in significant improvements in N and P removal, with a FEam of 15.23–25.86% in winter. Microbial N removal accounted for 71.57% of the total N removed in winter, and the decrease in plant uptake was the dominant factor in the wintertime decrease in N removal relative to that in late autumn. These results demonstrate the importance of cold-season plants in CFWs for the treatment of secondary effluent during cold winters.
Highlights
To identify the facilitation effect of a cool-season aquatic macrophyte (FEam) for use in effluent purification via constructed floating wetlands (CFWs) and to determine the possible pathways used during a winter period with an average temperature of less than 5 °C, pilot-scale CFWs were planted with the cold-season macrophyte Oenanthe clecumbens and were operated as batch systems
For constructed floating wetlands (CFWs) with aquatic macrophytes growing in a floating matrix[11], the conditions are different: the macrophytes generally act as the main CFW component that play a dominant role in pollutant removal[12]
Our experimental period featured both a warm autumn and a cold winter, suggesting the experimental period is appropriate for evaluating the purification ability of the cool-season aquatic macrophyte in FW in winter and comparing the performances between a cold winter and a warm autumn
Summary
To identify the facilitation effect of a cool-season aquatic macrophyte (FEam) for use in effluent purification via constructed floating wetlands (CFWs) and to determine the possible pathways used during a winter period with an average temperature of less than 5 °C, pilot-scale CFWs were planted with the cold-season macrophyte Oenanthe clecumbens and were operated as batch systems. Microbial N removal accounted for 71.57% of the total N removed in winter, and the decrease in plant uptake was the dominant factor in the wintertime decrease in N removal relative to that in late autumn These results demonstrate the importance of cold-season plants in CFWs for the treatment of secondary effluent during cold winters. For CWs with plants growing in a substrate, numerous studies have been conducted to quantify the purification function of aquatic macrophytes in the removal of pollutants and to understand the purification mechanism[8,18]. Little is known about the purification mechanism of CFWs in winter, such as whether the direct absorption by macrophytes or the activities of microbes play a more important role in the pollutant removal in winter?
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