Evapotranspiration versus oxygen intrusion: which is the main force in alleviating bioclogging of vertical-flow constructed wetlands during a resting operation?
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Clogging is the most significant challenge limiting the application of constructed wetlands. Application of a forced resting period is a practical way to relieve clogging, particularly bioclogging. To reveal the alleviation mechanisms behind such a resting operation, evapotranspiration and oxygen flux were studied during a resting period in a laboratory vertical-flow constructed wetland model through physical simulation and numerical model analysis. In addition, the optimum theoretical resting duration was determined based on the time required for oxygen to completely fill the pores, i.e., formation of a sufficiently thick and completely dry layer. The results indicated that (1) evapotranspiration was not the key factor, but was a driving force in the alleviation of bioclogging; (2) the rate of oxygen diffusion into the pores was sufficient to oxidize and disperse the flocculant biofilm, which was essential to alleviate bioclogging. This study provides important insights into understanding how clogging/bioclogging can be alleviated in vertical-flow constructed wetlands.
KeywordsConstructed wetland Bioclogging Resting operation Theoretical resting duration
Vertical-flow constructed wetland
Ordinary differential equation
Extracellular polymeric substances
The authors would particularly like to thank Dr. Chenming Zhang from the University of Queensland for his kind assistance during the preparation of the paper. The authors acknowledge financial support for this study from Natural Science Foundation of China (51509070, 91547206), Chinese Postdoctoral Science Foundation (2015M571779), and Fundamental Research Funds for the Central Universities (2015B15214). This study was also supported by the China Scholarship Council for a 1-year study at EPFL, Switzerland. The authors are grateful to Dr. Christine Watts for English corrections.
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