Biochemical reactor media characterization study

Abstract

BCRs, also known as sulfate-reducing bioreactors (SRBRs), are generally considered low maintenance passive treatment systems which require neither electricity nor continuous chemical inputs. In order to remain effective, the substrate from BCRs must be removed and replaced every so often as the organic matter and limestone are consumed. Substrate from a pilot scale BCR at the Golinsky Mine near Lake Shasta, California was studied upon decommission of the pilot test. The study examined geochemical stability of the substrate, in particular with respect to metals, in order to evaluate appropriate disposal options for the substrate. The study included elemental and mineralogical analyses, as well as different types of short-term leach tests. In addition, several zones, such as an oxide and sulfide zones, were identified vertically within the pilot cell substrate where different metals accumulated, depending on removal mechanisms. The stability of metals in the substrate appears dependent on the removal mechanism for the metals. For example, metals that appear removed as solid metal sulfides are susceptible to remobilization under oxidizing conditions, indicating the substrate should not be disposed of under surface conditions. Disposal options may vary by zone. Biochemical reactors (BCRs) are frequently used to effectively treat acid rock drainage (ARD). The subject of this study was a vertical-flow pilot BCR with treatment media consisting of, by weight, 40% co-gen fuel, 29% limestone chips, 10% hay, 10% rice hulls, 10% cow manure, and 1% ash. The pilot operated at a flow rate of about 3.8 Liters per minute for 26 months and treated low pH ARD with high concentrations of aluminum, iron, and zinc. Copyright © (2010) by the American Society of Mining & Reclamation.