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This study examined the effect of intermediate landfill addition on heavy metal concentrations during anaerobic digestion of sewage sludge from municipal wastewater treatment plant. A determination of average metal concentrations in the feedstock and digest were performed. The study was carried out in the reactor operating at a controlled mesophilic temperature of 30 stopni C and in semi-flow mode. Three runs with different doses of leachate were conducted. Analysis of total metal content in sludge and leachate was carried out. The concentrations of the following metals were determined: Al, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Zn. An observation of the changes of metal concentrations before and after digestion was carried out to evaluate the environmental impact analysis of digestied medium. The results indicated that metal concentrations in leachate were much lower than the values observed for the mixed sludge. The metal concentrations observed in the digests were comparable for all runs, thus the addition of leachate was not found as a deetrminant of the co-digestion effluent quality. The final metal concentrations of the dry sludge showed a general decrease in the levels of the specified metals as a result of co-digestion. This seems to indicate that co-fermentation of sewage sludge and landfill leachate could be considered as a harmless method of intermediate leachate utilization.
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