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?:abstract
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Vietnam, like many developing countries, is facing serious water quality issues due to discharging wastewaters without treatment or with improper treatment, which can constitute a potential risk for aquatic ecosystems, food safety and human health. Hybrid constructed wetlands with four substrate layers (HCW) and modified hybrid constructed wetland (MHCW-1 and MHCW-2) with seven substrate layers were designed to evaluate the enhanced treatment capacity for wastewaters. To this end, we carried out an outdoor experiment at the Vietnam Academy of Science and Technology, Vietnam to treat its wastewaters from April to August 2019. All constructed wetland units were planted with reed Phragmites australis and cyperus Cyperus alternifolius; and specifically wetland MHCW-2 was cultured with earthworm Perionys excavates. Results indicated that MHCW-1 and MHCW-2 with seven substrate layers had higher removal efficiencies of NO3--N, TKN and TP than HCW system. More substrate layers in MHCW-1 and MHCW-2 also resulted in increase of Cu and Pb removal efficiencies, with 73.5%, 79.4%, 71.5% and 67.8%, respectively. Particularly, earthworm addition in MHCW-2 was more efficient in decreasing the concentrations of biochemical oxygen demand (BOD5), with removal efficiency over 70%.
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