Webinars

Date & Time
April 14, 2026, 1:00 p.m. CT

Abstract
Certain biologically based passive treatment system process units (e.g., vertical flow bioreactors [VFBR]) may produce elevated concentrations of atypical non-mine drainage-related constituents, such as sulfide, oxygen demand, and nutrients. Excess sulfide is a source of nuisance odors and toxicity. Aqueous sulfide concentrations greater than 0.002 mg/L are considered chronically ecotoxic, and prolonged human exposure to gaseous concentrations greater than 20 ppmv leads to health effects. Oxygen demand can reduce dissolved oxygen concentrations in receiving streams (sometimes to below 1 mg/L), which harms aquatic life. Excess nitrogen and phosphorus may cause eutrophication.

These constituents are not typically included in most passive treatment system monitoring schemes and performance evaluations. However, they have been evaluated in two passive treatment systems at the Tar Creek Superfund Site, the Oklahoma portion of the abandoned Tri-State Lead-Zinc Mining District. Seasonal production of nuisance constituents was determined at both sites in their first few summers of operation. At both sites, solar- or wind-powered re-aeration devices addressed VFBR effluents. At one site, a novel, custom-designed, solar-driven sulfide-removal system using an activated carbon filter was evaluated. Initially, sulfide, oxygen demand, nitrogen, and phosphorus concentrations were elevated in VFBR effluents. Aqueous concentrations and gaseous sulfide levels were consistently above applicable criteria during the initial startup period. However, in both cases, after system stabilization in the first few years, nuisance constituent production was below potentially problematic levels, but mine drainage treatment performance continued.

The systems have been in continuous operation for 17 and 9 years, respectively, and have resulted in documented ecological recovery of the receiving stream.