Browsing by Subject "sulfate reduction"

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    Mobile Water Treatment Demonstration System for Sulfate Reduction
    (University of Minnesota Duluth, 2022-08) Cai, Meijun; Rao, Shashi; Post, Sara P; Hanson, Adrian; Chun, Chan Lan; Johnson, Lucinda B; Hudak, George J; Weberg, Rolf
    The State of Minnesota adopted a sulfate standard of 10 mg/L for wild rice waters in 1973. Although under review, current technology for achieving this standard is a challenge for small industries and municipalities. Membrane-based technologies such as nanofiltration and reverse osmosis are capable of treating water to reach the Minnesota wild rice water sulfate standard; however, they typically require high capital and operation costs. Therefore, there is a need to develop cost-effective sulfate treatment alternatives. The Natural Resources Research Institute (NRRI) has developed a treatment system based on barite chemical precipitation reactions to reduce sulfate levels in water from 60-200 mg/L to below 10 mg/L. This system was demonstrated at bench-scale batch and continuous tests. The data collected from these lab tests were used to scale up the process to a trailer-based modular demonstration treatment system. This study highlights the outcomes of field pilot tests conducted by NRRI using this treatment system. The objectives of the field pilot trials were to: (1) Evaluate the efficacy of the chemical precipitation process when scaled up from 200 ml/min to 2 GPM; (2) Study the effect of co-existing chelating organics of the raw wastewater on barite precipitation reactions; (3) Optimize the chemical reagent dosage levels; (4) Investigate the potential of reusing process sludge to promote precipitation reactions; (5) Identify strategies to minimize scale formation on process equipment; and (6) Estimate the chemical reagent costs. The pilot tests were conducted using effluent from two municipal wastewater treatment plants (WWTP)—the Virginia WWTP and the Grand Rapids WWTP in northeastern Minnesota—from June 2021 until October 2021.
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    Using reactive transport modeling to link hydrologic flux and root zone geochemistry at Second Creek, a sulfate enriched wild rice stream in northeastern Minnesota
    (2017-02) Yourd, Amanda
    Wild rice (Zizania palustris) is an economically, culturally, and ecologically important aquatic plant species in Minnesota. In northeastern Minnesota, iron ore and taconite mining have led to elevated surface water sulfate concentrations, which has raised concern about the potential of sulfate negatively impacting wild rice populations. Recent studies have shown that elevated sulfide concentrations in the wild rice root zone (sediment porewater) is more closely correlated with lower occurrence of wild rice than surface water sulfate. This toxic porewater sulfide can be attenuated by precipitation of iron sulfide minerals if dissolved ferrous iron is locally available. Although these geochemical reactions occur in the sediment porewater, or hyporheic zone, where groundwater and surface water mix, the effect of groundwater flux and geochemistry on geochemical processes within the hyporheic zone has not been examined in the context of wild rice and sulfate. Here, we use physical and geochemical field data collected from surface water, porewater, and groundwater to inform a reactive transport model of Second Creek, a mining impacted wild rice stream in northeastern Minnesota. The model is implemented for different hydrologic flux regimes in different locations at Second Creek to examine the geochemical response of the sediment porewater to changes in both physical and geochemical conditions. We show that porewater sulfide concentrations can are dependent on hydrologic flux direction and magnitude, as well as on concentrations of surface water sulfate, sediment organic carbon, and porewater iron. This work emphasizes the importance of constraining groundwater flux and geochemistry when examining processes at the groundwater-surface water interface.