Mineral processing residue use as substrate in a modular engineered wetland for wastewater treatment

Safeguarding the water quality of Poyang Lake, China's largest freshwater lake, is essential for long-term regional water resource sustainability. The use of locally-available mineral processing residues as reactive substrate in engineered wetlands may provide a cost-effective treatment alternative for mixed agricultural and domestic wastewaters entering Poyang Lake. In this study, Chinese iron- and steel-making slags and a titanium mineral processing residue with high nutrient removal capacity were identified in laboratory experiments. A pilot-scale modular wetland system consisting of free water surface, and vertical and horizontal subsurface flow units, all planted with locally-available vegetation, was constructed at the Poyang Lake Modelling Experiment and Research Base in Jiangxi Province. Assessment of nutrient removal efficiency and effluent water quality was undertaken to inform upscaling and optimization of the modular unit process wetland design. The pilot-scale wetland system removed 55% of inorganic N in influent wastewater and was particularly effective in P attenuation, removing 81% of total P. The environmentally-acceptable pH of wetland system effluents, along with low concentrations of dissolved metals and the absence of potential for either N- or Si-limitation, indicated that the modular wetland system examined was potentially suitable for treatment of mixed wastewater entering Poyang Lake. The use of the selected mineral processing residues as reactive substrate in engineered wetland systems enhanced pollutant removal processes in the modular engineered wetland system, effectively attenuating pollutants in mixed wastewater.