Heavy metals in sludge produced during production of drinking water from surface sources

Abstract

Samples of water and sludge were analysed from two different water treatment plants which produce drinking water from surface sources taken in two territories with different geology. In one territory, polymetalic deposits of Cu, Pb, Zn are located (primary rocks – Kulm). The second territory is located in the flysch range with no presence of heavy metals. Concentration of heavy metals (Cu, Cr, Ni, Pb, Cd, As, Hg, B) in water was below detection limits. Analyses of the sludge produced during coagulation filtering treatment have proved presence of heavy metals in the sludge. Following metals in the sludge: As, Cd, Cr, Cu, Hg, Mo, Ni, Pb, Zn. Most heavy metals are of anthropogenic origin. It is only Zn and As which originate in the geology of the catchment area. The heavy metal concentrations were low, the exception being As which was 30.6 mg/kg in dry mass of sludge for the Podhradí water treatment plant. This value is three times higher than the limit permitted for the sludge. Regular monitoring of heavy metal concentration in the water treatment sludge will improve assessment of presence of the heavy metals in the treated water.