Water Quality Based Design Guidelines for Successive Alkalinity-Producing Systems Used in the Treatment of Acidic Mine Drainage

Abstract

Successive Alkalinity-Producing Systems (SAPS) have proven to be a viable alternative to chemical treatment for renovating acidic mine drainage (AMD). The lack of water quality based design guidelines, however, is believed to be a cause of the variability of SAPS performance in the field. This study monitored eight SAPS systems for the purpose of determining the effect of influent water quality and system design on system performance. Monthly water quality data were obtained for each system over periods ranging from 3 to 5 years. All systems demonstrated an ability to generate alkalinity and/or neutralize acidity. These systems revealed significant correlations between net alkalinity production and log residence time (r = 0.7414), influent total iron (r = 0.7357), and influent non-manganese acidity (r = 0.6919). From these relationships, a calibrated model was developed for predicting SAPS net alkalinity generation. As a compliment to the field study, a series of laboratory-scale SAPS columns were studied for a period of 12 months to examine the effect of residence time on system performance and to monitor the internal changes in water quality. The columns were operated at residence times of 17, 30, 60 hours with three replicates each and were subject to ambient temperature fluctuations. Data revealed that systems with residence times below 25 hours in the organic layer were unable to adequately reduce dissolved oxygen concentrations in the organic layer to prevent limestone armoring. The results of this study suggest water quality based guidelines for designing SAPS systems.