Date of Award
Master of Science (MS)
Mine-influenced water (MIW), a waste water product containing heavy metals and sulfates, is a significant pollution source to waters in Montana. Implementing a low cost, passive treatment system, such as a sulfate-reducing bioreactor (SRBR), is desired for remediation of streams influenced by heavy metals in remote locations. SRBR systems operate by using organic matter and sulfate-rich water to precipitate and immobilize dissolved heavy metals. Sulfate-reducing bacteria utilize the organic matter as an electron donor to convert sulfate to sulfide, and then sulfide in the bioreactor is utilized to precipitate heavy metals. Under ideal operating conditions, SRBR systems can remove >98% of dissolved heavy metals. However, heavy metal removal efficiency is compromised by cold climates, acidic conditions, impaired hydraulic conductivity and introducing oxygen into the system. Previous published studies have research design modifications to improve SRBRs to overcome these operating challenges. These modifications included adding a liquid carbon source, limestone and adsorbents. Physical adsorption is a reversible process, and therefore has potential to supplement SRBR systems throughout inhibited performance during winter months with continued regeneration in the summer time, and permit further reuse. This research investigated design enhancements to SRBR systems to improve winter-time heavy metal treatment using an adsorbent material with the intent to apply this technology to an impaired stream in Butte, MT, Grove Gulch, which is affected by mine tailing in the water shed along its banks.
Experiments were carried out to characterize temperature effects on SRBR systems, examine isolated adsorption-desorption effects, and apply adsorbent materials within an SRBR to quantify the extent of heavy metal removal under cold temperature conditions. Initially, batch experiments in flasks were carried out to assess the ability for adsorption of heavy metals to an adsorbent, followed by desorption and precipitation of heavy metals allowing for reuse of the adsorbent. Batch desorption experiments were variable, yet demonstrated potential for regeneration of the selected adsorbent, granular activated carbon (GAC). Desorption and precipitation of copper and zinc varied from 14-91%. The investigated bench-scale SRBR removed >98% of influent copper and zinc ions operating under summer-time conditions (22°C). Winter-time operating conditions (5°C) resulted in decreased removal efficiencies of copper (88-99.98%) and zinc (52-99.91%). The success of this project determined that SRBR systems have the potential to adequately operate in a cold climate region, such as Butte, MT, using a supplementary adsorbent material. Heavy metal removal in the SRBR using GAC to supplement the reactor under winter-time conditions was 85-99%. Microbial activity was hindered while influenced by winter-time operating conditions, but did not diminish. Research findings revealed the potential for adsorption of heavy metals during winter-time conditions, followed by desorption and precipitation during summer months. The discoveries of this thesis raised further potential research questions and recommendations for full-scale operation.
Moreira, Katrina, "DESIGN IMPROVEMENTS TO SULFATE-REDUCING BIOREACTORS FOR MINE-INFLUENCED STREAM REMEDIATION IN COLD CLIMATES" (2018). Graduate Theses & Non-Theses. 163.