Influence of the ˇSoˇstanj coal-fired thermal power plant on mercury and methyl mercury concentrations in Lake Velenje, Slovenia

Lake Velenje is located in one of the most polluted regions in Slovenia, the ˇSalek Valley. The major source of pollution in the valley is the coal-fired thermal power plant in ˇSoˇstanj ˇSTPP, capacity 775 MW.. It has five separate units. All units have electrostatic precipitators for fly ash removal. Unit 4 also has installed a wet flue gas desulfurisation system FGD system.. Total mercury THg. concentrations were measured in lignite, slag and ash samples from the ˇSTPP. In flue gas, different mercury species THg, MeHg, Hg2q, Hg0 . were determined separately for unit 4 and unit 5 which use different flue gas cleaning technology. Mercury and methyl mercury MeHg. concentrations were also measured in lake water at different depths, in inflow water, outflow water, rain, snow and lake sediments in order to establish the influence of the power plant on the lake. Most mercury emitted from the power plant is in the elemental form. The ratio between oxidised and elemental Hg depends on the flue gas cleaning technology. Mass balance calculations have been performed for the ˇSTPP. The results show that the major sources of mercury in Lake Velenje are wet deposition and lake inflows. Total and MeHg concentrations in the water column are very low and can be compared to other non-contaminated freshwater lakes in the world