Influence of the Sostanj 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, th e Salek Valley. The major source of pollution in the valley is the coal-fir ed thermal power plant in Sostanj (STPP, capacity 775 MW). It has five sepa rate units. All units have electrostatic precipitators for fly ash removal. Unit 4 also has installed a wet flue gas desulfurisation system (FGD syste m). Total mercury (THg) concentrations were measured in lignite, slag and a sh samples from the STPP. In flue gas, different mercury species (THg, MeHg , Hg2+, Hg-0) were determined separately for unit 4 and unit 5 which use di fferent flue gas cleaning technology. Mercury and methyl mercury (MeHg) con centrations 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 eleme ntal Hg depends bn the flue gas cleaning technology. Mass balance calculati ons have been performed for the STPP. The results show that the major sourc es of mercury in Lake Velenje are wet deposition and lake inflows. Total an d MeHg concentrations in the water column are very low and can be compared to other non-contaminated freshwater lakes in the world. (C) 2000 Elsevier Science B.V. All rights reserved.