Cunha, Mirabelle ; Ferraz, Rafael ; Sancinetti, Giselle; Piacentini Rodriguez, Renata
Acid mine drainage (AMD) is among the most serious threats to water and the typical alkali-based treatment costs are high. This study’s main objective was the establishment of a highly efficient biological process using an upflow anaerobic sludge blanket (UASB) reactor to treat AMD based on a shorter hydraulic retention time (HRT) and lower organic matter input. The process was evaluated for a long-term operation (739days) in terms of the influence of HRT (14-24h), metal addition, sulfate loading rate (0.5-2.6gSO(4)(2-)l(-1)d(-1)), and the COD/SO42- ratio (0.67-1.0) using ethanol as the only electron donor at a pH of 4.0. Neutral effluent pH was achieved throughout the time apart from operational modifications. The reduction in HRT from 24 to 16h and an increase in the sulfate loading rate (SLR) up to 2.25gSO(4)(2-)l(-1)d(-1) improved the sulfate removal to (92.1 +/- 1.8)% with 80% chemical oxygen demand (COD) removal. However, the sulfate reduction was less than 80% when the HRT and SLR was changed to 14h and 2.6gSO(4)(2-)l(-1)d(-1), respectively. The oxidation of organic matter by sulfate reduction was greater than 50% regardless of the conditions imposed but the use of ethanol to treat AMD was more efficient when either the HRT was 16h (1.5gSO(4)(2-)l(-1)d(-1)) in the presence of Fe, Zn, and Cu or the HRT was 14h (2.6gSO(4)(2-)l(-1)d(-1)) but the COD/SO42- ratio was reduced to 0.67. The fully optimized conditions of the UASB reactor were set at an HRT of 16h, SLR of 1.5gSO(4)(2-)l(-1)d(-1), and a COD/SO42- ratio of 1.0.