Performance and microbial response in a multi-stage constructed wetland microcosm co-treating acid mine drainage and domestic wastewater

Multi-stage constructed wetland microcosms (mixing and sedimentation pond (MS), vertical-flow constructed wetland (VFCW) and surface-flow constructed wetland (SFCW)) were designed to co-treat high-strength acid mine drainage (AMD) and domestic wastewater, with agricultural waste (straw and cow manure) fermentation liquor as stimulation substrate. The 270-day lab-scale study showed that this system was highly effective in enhancing effluent pH (from 2.5 to 8.1) and removing dissolved metals (89.4% of Mn, and 99% of Fe, Zn, Cd and Cu), sulfate (51.9%) and organic/nutrient pollutants (COD, NH4+-N, NO3--N, and TP). The mixing and sedimentation pretreatment could alleviate the burden (strong acidity and high-strength metals) and clogging of wetlands, and the formed metal-rich sludge offered the possibility of metals reclaiming. Quantitative supplementary of fermentation liquor promoted sulfidogenic activity in VFCW, also avoiding excessive release of organic/nutrient pollutants. SFCW was effective in treating residual metals (especially Mn) and organic/nutrients. High-throughput sequencing test showed that the diverse microbe (such as sulfate reducing bacteria, nitrifying bacteria, and denitrifying bacteria) co-existing in this multi-stage system predominantly contributed to the effective remediation. Metal amounts assimilated by wetland plants were very limited (e.g. 1% for Mn) for metals remediation. The multi-stage constructed wetlands co-treatment system quantitatively supplied with liquid waste as carbon source may offer a promising eco-technology for the remediation of AMD.