Responding to Minnesota’s Regulatory Sulfate Standard for Wild Rice Waters
Johnson, Lucinda (1); Cai, Meijun (1); Chun, Chanlan (1); Hanson, Adrian (2); Shashikaran, Shashi (1); Hudak, George (1); Johnson, Nathan (2); Kolomitsyn, Igor (1); Deen, Tobin (1); Bernhardt, Beth (1)
1: Natural Resources Research Institute, University of Minnesota, United States of America; 2: Dept. Civil Engineering, University of Minnsota Duluth, United States
Sulfate removal is a common challenge for industries such as mining, power generation and the petrochemical industry. A common method for removal of sulfate from wastewaters involves neutralization with lime which reduces the concentration to the solubility limit of 1200 mg/L. Biological treatment requires longer retention time, releases toxic hydrogen sulfide gas and has a limited ability to remove sulfate below 50 mg/L. The state of Minnesota (USA) has a restrictive standard of 10 mg/L for waters associated with wild rice; this poses a significant challenge for wastewater treatment facilities, small businesses, mining, and paper industries. Existing technologies (e.g., reverse osmosis; ultrafiltration) can achieve this standard, but are expensive and generate significant waste products. We are developing novel products and technologies for removing sulfate cost-effectively, while also reducing the need for significant waste handling.
First, we have developed a new material with novel chemical and physical properties created from peat resources. We introduced anion exchange properties to this material and have reached a 125 mEq/100 g of total capacity. Anion exchange properties would allow for selective removal of sulfate anions from waste and mine water at various pH levels.
Sulfate removal via barite precipitation has recently gained attention, as sulfates readily precipitate with barium salts as insoluble barium sulfate. We are testing chemical precipitation processes for treating municipal wastewater. However, it is not clear whether this application can be use effectively, because this waste is dilute relative to other industrial waters. Through batch experiments and a bench-scale continuous flow laboratory study we demonstrated that it is practical to use barium chloride to precipitate sulfate (barite method) to levels below 10 mg/L.
Finally, we have developed a bioreactor to stimulate biological sulfate reduction and simultaneously facilitate the removal of the reduced sulfide by applying iron electrolysis under low electrical potential. The efficacy of sulfate reduction and sulfide precipitation were tested in systems inoculated with sediment microbial consortia.A synthetic mine water medium with 1000 mg/L sulfate was treated under a 0-2V electric potential where cathodic hydrogen and anodic iron dissolution occurred. This study will result in a proof-of-concept application of electrical potential to provide electron donor substrates to biological sulfate treatment with simultaneous sulfide removal with iron species in a controlled manner.
Addressing Minnesota’s unique regulatory standard will require application of multiple technologies, which we hope can be achieved through multidisciplinary approaches.