In this study, a high organic loading rate of 58–146 g BOD5/m2 day with a hydraulic loading rate (HLR) of 1.63 m3/m2 day and retention time (RT) of 16 h was achieved to maximize the treatment capacity of a four-stage alum sludge-based constructed wetland (CW) system. An alternative operation strategy, i.e., the first stage anaerobic up-flow and the remaining stage tidal flow with effluent recirculation, was investigated to achieve the goal with good treatment performance of 82% COD, 91% BOD5, 92% SS, 94% NH4-N, and 82% TN removal. Two kinetic models, i.e., first-order model and Monod plus continuous stirred-tank reactor (CSTR) flow model, were employed for predicting the removal dynamics. The results showed that the tidal flow strategy enhances oxygen transport and diffusion, thus improving reduction of organics and NH4-N. Effluent recirculation could further increase elimination of organics by extending the interaction time and also benefit the denitrification process. In addition, denitrification could be further enhanced by anaerobic up-flow in the first stage.
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The authors greatly acknowledge the research financial support from the National Natural Science Foundation of China (grant numbers: 41302208 and 41572235). The first author would like to thank University College Dublin for the Ad Astra scholarship.
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1.Key Laboratory of Water Supply and Drainage, Ministry of Housing and Urban-Rural DevelopmentChang’an UniversityXi’anPeople’s Republic of China
2.Key Laboratory of Urban Stormwater System and Water Environment/R&D Centre for Sustainable Wastewater TreatmentBeijing University of Civil Engineering and Architecture, Ministry of EducationBeijingPeople’s Republic of China
3.UCD Dooge Centre for Water Resources Research, School of Civil EngineeringUniversity College DublinDublin 4Ireland
4.Department of Soil Water Land Engineering and Management, Vaugh School of Agricultural Engineering and TechnologySam Higginbottom Institute of Agriculture, Technology & SciencesAllahabadIndia