Evaluating locally available organic substrates for vertical flow passive treatment cells at Cerro Rico de Potosí, Bolivia

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. In the high elevation desert of Potosi, Bolivia, the low productivity landscape limits the availability of sustainable and economical organic substrates. Locally available brewery waste, llama manure, and cow manure were evaluated as potential VFC substrates in a preliminary laboratory fed-batch study to assist in passive treatment system design. Two abandoned AMD discharges were collected from Cerro Rico de Potosi. Discharge A had an initial pH of 2.96, specific conductance of 3.31 mS/cm, and acidity of 1,350 mg/L as CaCO3 equivalent. Discharge B had an initial pH of 3.85, specific conductance of 1.87 mS/cm, and acidity of 1,000 mg/L as CaCO3 equivalent. Triplicate fed-batch reactors were set up in 1-L cubitainers with each potential substrate exposed to each AMD, yielding a total of 18 reactors exposed for 9 days and sampled two times for anions and dissolved metals. Cow manure reactors exhibited the greatest pH and alkalinity increases. Cd, Co, Fe, Mn, Ni, Pb, and Zn decreased in all reactors. SO4 concentrations only decreased in brewery waste reactors. However, SO4 reducing bacteria was higher for cow manure reactors. Results suggest that llama and cow manure are the more labile substrates, with llama manure being the most affordable. Brewery waste could be a suitable less-labile long-term substrate amendment. However, longer-term studies are needed to determine the optimum VFC substrate mixture in this unique circumstance.