Effective Attenuation of Nutrients in Mixed Wastewaters Using Mineral-Based Waste Materials As Reactive Substrate in Constructed Wetlands.

Constructed wetlands with reactive mineral substrate for enhanced contaminant attenuation may provide effective low-cost treatment of wastewaters, particularly in rural areas with limited access to centralised treatment facilities.  Poyang Lake in Jiangxi Province is China’s largest freshwater lake and safeguarding of Poyang Lake water quality is critical to ensure the long-term sustainability of water resources in Jiangxi Province.  Use of locally-available waste materials as reactive substrate in constructed wetlands potentially offers a cost-effective treatment option for agricultural and domestic wastewaters entering Poyang Lake.  In the present study, mineralogical, geochemical and radiochemical characterisation concomitant with ecological toxicity testing and laboratory column trials facilitated identification of locally-sourced iron- and steel-making and titanium mineral processing residues with high nutrient and/or metal sorption capacities.  A pilot-scale hybrid constructed wetland system consisting of free water surface flow, horizontal subsurface flow, and vertical subsurface flow wetland modules, all planted with locally-available vegetation, was constructed at the Poyang Lake Modelling Experiment and Research Base.  Detailed assessment of nutrient removal efficiency and effluent water quality were undertaken under controlled field conditions to facilitate optimization of the constructed wetland design prior to full-scale implementation of constructed wetlands for wastewater treatment.  The hybrid constructed wetland system removed 55% of the inorganic nitrogen in influent wastewater and was particularly effective for phosphorus attenuation, removing 81% of the total phosphorus.  The environmentally-acceptable pH of constructed wetland system effluents along with low concentrations of dissolved metals and the absence of potential for either N- or P-limitation indicated that the hybrid treatment wetland system examined is suitable for wastewater treatment in Jiangxi Province.  The mineral-based residues used as reactive substrate in the hybrid constructed wetland system demonstrate suitability for use as treatment media in constructed wetlands, drain liners, permeable reactive barriers or similar applications in areas without access to centralised wastewater treatment facilities.