English

Abstract

Vertical flow cells (VFCs) are key components of passive acid mine drainage (AMD) treatment systems and require organic substrates that create anaerobic conditions and encourage bacterial sulfate reduction. Sustainable and economical substrate options are often locally available organic waste materials. In the high elevation desert of Potosi, Bolivia, the low productivity landscape limits their availability. In this study, several locally available organic wastes were identified and evaluated as potential VFC substrates in a preliminary laboratory batch study to assist in passive treatment system design. Brewery waste, llama manure and cow manure were collected from three nearby locations. Two abandoned mine water discharges with different properties were collected near Cerro Rico de Potosi. Discharge water A had an initial pH of 2.96, a specific conductivity of 3.310 mS/cm and acidity of 1350 mg/L as CaCO3 equivalent. Discharge water B had an initial pH of 3.85, specific conductivity of 1.867 mS/cm and acidity of 1000 mg/L. Triplicate batch reactors were set up in 1-L cubitainers with each potential substrate exposed to each AMD, yielding a total of 18 bioreactors which were exposed for 9 days and sampled two times for analysis of anions and dissolved metals. Substrate samples were collected for microbial analysis including iron reducing bacteria (IRB), sulfate reducing bacteria (SRB), fermenters and nitrifiers. Cow manure reactors exhibited the greatest pH, alkalinity and specific conductance increases. Brewery waste reactors did not show any increase in pH. However, sulfate concentrations only decreased in brewery waste reactors, from 2595 mg/L in discharge water A and 1105 mg/L discharge water B to 1350±202 mg/L and 669±31 mg/L respectively. Discharge water A had a minimal impact on microbial groups tested. SRB populations were higher for brewery and cow manure reactors. Fermentative bacteria were higher in llama and cow manure reactors. Results from this short-term experiment suggest that llama and cow manure may be appropriate locally available substrates. Additional longer-term studies are needed to determine the best mix of substrates to be used in a VFC in Potosi, Bolivia.