DOES CRYPTIC SULFUR CYCLING IN AN AMD PASSIVE REMEDIATION SYSTEM PREVENT THE REMOVAL OF HIGH SULFATE CONCENTRATIONS?

Abandoned mine drainage (AMD) in Pennsylvania is largely the result of extensive coal mining. Currently, there are 5500 miles of streams impacted by AMD in Pennsylvania alone. Once the geochemical processes of AMD start they cannot be stopped, only treated. Passive remediation systems are an affordable option for treating AMD and have proven to have long term success. In systems that treat circum-neutral discharge, heavy metals are successfully removed from the system, while sulfate levels remain high throughout. The Lowber Passive Remediation System in southwestern Pennsylvania (40.250394, -79.764429) treats a circum-neutral AMD discharge with high levels of iron (38-50 PPM) and sulfate (960 -1250 PPM). While the system successfully removes the iron from the water by time it reaches the effluent, sulfate eludes remediation efforts and remains constant throughout. Despite no measurable changes occurring in sulfate levels throughout Lowber, we have found high levels of both sulfur-oxidizing and sulfate-reducing bacteria present. This suggests rapid sulfur cycling may be leading to no net change in sulfate levels. In vitro studies show that we can drive complete sulfur reduction to sulfide and subsequently metal sulfide formation with the addition of lactate. This not only shows that the organisms are present, but are capable of complete sulfur reduction in vitro. If sulfur cycling can be driven unidirectional towards sulfide formation, not only can sulfate levels be decreased, but stable metal sulfides can be formed. The understanding of sulfur cycling occurring in these systems is paramount to remediation efforts.