Ranking and Assessment of Sequential Passive Treatment of Acid Mine Drainage Using Water Quality and Pollution Indices

Abstract

Some mining sites generate acid mine drainage (AMD)—a highly acidic, metal-rich waste stream that affects bodies of water. Passive treatment systems are widely being adapted, particularly for abandoned or closed mines, due to their cost-effectiveness and lower environmental impact. However, novel strategies and approaches still need to be developed, especially in their implementation. Through batch experiments, this study identifies the effective sequence of three locally available treatment media, namely limestone (LS), steel slag (SS), and activated carbon (AC), using various water quality and pollution indices (WQPIs). The performance of the sequences was assessed based on their ability to improve various in situ parameters (pH, oxidation–reduction potential (ORP), dissolved oxygen (DO), and electrical conductivity (EC)) and their efficiency in removing Fe, Mn, Cu, and SO42−. Six sequences of media were identified and ranked by calculating a score based on comparisons with the Philippine General Effluent Standard (GES) by normalization and specific WQPIs for AMD and AMD-impacted waters, such as the CCMEWQI, MAMDI, and WPI-AMD. Analysis showed that the sequence of LS-AC-SS and SS-LS-AC yielded the highest removal for heavy metals (98.78% for Fe and Mn and 89.92% for Cu). However, limited removal of SO42− was observed (14.96%), which suggests that additional treatment beyond the materials explored must be considered. Considering all the parameters and assessing them through normalization and WQPIs, the sequence of SS-LS-AC achieved the overall best treatment performance. Differences were observed in the ranking between the methods, with WQPIs successfully capturing actual water quality, demonstrating its robustness as an assessment tool. This study shows that the treatment media sequence is a factor in treating AMD, specifically utilizing AC, SS, and LS.