Abstract
Abstract The main goal of this study was to develop a cost-efficient biological method for the removal of sulfate from mining effluents in cold conditions. A consortium of cold-tolerant sulfate-reducing bacteria (SRB) was tested at 6 °C regarding the utilization of economically viable, low-cost carbon sources, i.e., whey, conditioned sewage sludge, and peat, in the removal of sulfate from synthetic mining water. Succinate was used as a reference carbon source. Of all the studied low-cost carbon sources, conditioned sewage sludge proved to be the most efficient. Nuclear magnetic resonance (NMR) spectroscopy revealed that sewage sludge contained propionic acid, which proved to be utilizable by SRB under cold conditions. Peat both adsorbed the sulfate and acted as a nutrient source in the sulfate reduction process. When whey was used as a carbon source, only a slight decrease in sulfate concentration was detected. Succinate was found to work in a truly predictable and efficient way as a carbon source in biological sulfate reduction, even at the lowest concentration tested. The use of conditioned sewage sludge increased the bacterial diversity in liquid cultivations significantly. However, the number of SRB was highest in the succinate cultivations.
Highlights
Mining is one of the main causes of the contamination of natural water bodies with sulfate and toxic metals
Nuclear magnetic resonance (NMR) spectroscopy revealed that sewage sludge contained propionic acid, which proved to be utilizable by sulfate-reducing bacteria (SRB) under cold conditions
It should be noted that the carbon sources contained insoluble solids, which might have degraded during the bacterial cultivation and increased the COD and nutrient concentrations
Summary
Mining is one of the main causes of the contamination of natural water bodies with sulfate and toxic metals. Growth in rainfall and surface runoffs can even increase the amount of contaminated waters. Further treatment of mining waters has been implemented due to tightening environmental permit conditions. The leakage of untreated mining waters into the environment has taken place repeatedly around the world. In Finland, the limits for concentrations of sulfate and metals in mining effluent discharge are specific to each mine and the limits for sulfate may vary considerably (Nurmesniemi 2018). The leakage of sulfate-containing effluents into nature can cause enormous environmental problems. Sulfate ions cause the salinization and stratification of fresh waters, which in turn leads to hypolimnetic oxygen depletion (Kauppi et al 2013). The consequences of anoxia are a decrease in biodiversity and changes in aquatic ecosystems (Williams 2001)
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