Defence of PhD thesis on wastewater treatment

A PhD study at University of Oulu has been performed by Hanna Virpiranta as part of the Kolarctic CBC SEESIMA project. The topic is “Development of biological treatment for sulfate- and metals-containing cold mining-impacted waters”. Hanna will now defend the thesis on the 24th February 2023 at the Arina auditorium (TA105), Linnanmaa, Oulu.

The PhD study developed a biological treatment process suitable for cold regions, using sulfate-reducing bacteria. The sulfate-reducing bacteria were obtained from a sediment sample from the boreal region and were adapted to the cold conditions. Initially succinate was used as the carbon source, but the use of different lower-cost carbon sources was also studied (such as sewage sludge, peat and whey), as well as synthetic and actual mine wastewaters.

After initial batch experiments the studied continued with the use of a continuous up-flow biofilm reactor, the layout of which is depicted in the diagram above (from Virpiranta et al 2022). The sulfate-reducing bacteria consortium was found to be able to grow at temperatures as low as 6 degC. At a temperature of 11,7 degC the rate of removal of sulfate was 4500 mg/( and 87% of the original sulfate was removed. The reduction of sulfate formed hydrogen sulphide that caused the precipitation of most of the metals present in the wastewater. A further application of the sulfate-reducing bacteria was also investigated for the bioregeneration of ion exchange resin used for further sulphate removal from the waterwater. In lab-scale column experiments the resin capacity was almost completely restored.

The results of this study provide valuable information about the use of biological sulfate reduction for the treatment of Mine-impacted waters in cold regions, and the combination of sulphate reduction and ion exchange as treatment methods.

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