DETAILED INVESTIGATION AND REMEDIATION OF ACID MINE DRAINAGE IMPACTED WATER

Abstract

Acid mine drainage (AMD) is a global environmental problem associated with mining in regions with economic minerals associated with reduced sulfur species like pyrites and marcasites. AMD is a major source of land and water pollution. It is caused by oxidation of reduced sulfur species into sulfate upon contact with oxygen and water and the subsequent release of H+ in the process.Thus, the pH of the affected water is further lowered, and the sulfate and dissolved solids concentration is elevated. The primary characterization of coal acid mine drainage (CAMD) is based on physico-chemical characteristics like- pH, sulfate concentration, metal concentration, solids concentration, oxidation reduction potential (ORP), and electrical conductivity (EC). The results confirmed generation of AMD in the active coal mining region and demonstrated a novel bioreactor configuration to control the resulting water pollution. The study provides an insight into the engineered application of dissimilatory sulfate reduction (DSR) along with role of improved bio-carriers in continuous flow anaerobic systems applicable for treatment of AMD. The first objective of this study was to characterize the physico-chemical properties of mining impacted water at strategically important coalfields in Assam and Telangana states of India, with high and low Sulfur content coal, respectively. The collected water samples from both sites exhibited low pH, high sulfate, conductivity, dissolved solids, iron and manganese, typical of AMD. The next objective was to develop a cost-effective remediation technology for the identified CAMDs by minimizing the organic electron donor dosage and supplementation with low-cost alternatives like molasses. Currently, lime-based neutralization of CAMD is practiced at the mines which generates bulky hydroxide sludge and extremely high pH values. Biological treatment via dissimilatory sulfate reduction (DSR) is a popular practice to treat high sulfate wastewater, and is effective under low pH conditions. Hence, an active treatment system based on up-flow anaerobic packed-bed column bioreactor was envisaged in this study as a suitable solution for neutralization of CAMD. In this study, the bioreactor start-up, stabilization, acclimatization to acidic conditions and performance under varying operational parameters like temperature, organic electron donor composition and dose, and hydraulic retention time (HRT) were reported. pH, ORP, alkalinity, sulfate, chemical oxygen demand (COD), and sulfide concentration were measured to monitor the treatment efficiency under each set of conditions. The bioreactor performance was evaluated based on the increase in pH value, sulfate reduction efficiency (SRE) and COD removal efficiency (CRE).