Enhanced treatment of reclaimed water using functional manganese-sand media in constructed wetlands

Reclaimed water is an alternative water source that can help replenish natural lakes and rivers， alleviating issues such as water scarcity， flow disruptions， and poor water flow. Residual pollutants in reclaimed water could pose an ecological danger. Therefore， a pilot-scale hybrid vertical flow constructed wetland system， filled with manganese ore sand， quartz sand， and cobblestones， was constructed and operated for about 140 days. During this operation period， the efficiencies in removing nitrogen， phosphorus， and organic matter were studied. Also， the potential ecotoxicological effects exhibited by the purified reclaimed water were investigated. The practicality for the use of manganese ore sand as a functional filler was also assessed. The results demonstrated that after 2 to 3 months of operation， the removal efficiencies for ammonia and phosphate maintained above 90% and 80%， with their influent concentrations below 0.4 mg/L and 0.2 mg/L， respectively. With influent concentrations of 4 to 8 mg/L for nitrate and below 30 mg/L for oxygen-consuming organic matter （measured as COD）， their average concentration reductions remained below 1.0 mg/L and 5 mg/L， respectively. The manganese ore sand enhanced the decomposition and removal of residual organic matter， achieving 48% of reduction in 3D fluorescence intensity， a 38% decrease in UV254， and 70.8% in the removal of four target antibiotics. The reclaimed water after treatment exhibited no significant genotoxicity， its cell micronucleus rate approached that of tap water levels， and non-concentrated samples showed no acute biotoxicity. This study provides technical support for enhancing reclaimed water quality and controlling associated ecological risks.