engleski

Trace metals fluxes in the wastewater treatment plant of the city of Zagreb and their impact on the Sava River

A study of trace metals fluxes in the wastewater treatment plant (WWTP) of the city of Zagreb was performed over a period of 8 months in 2009. Total and dissolved concentration of 26 elements ( Ag, Al, As, Ba, Bi, Cd, Co, Cr, Cs, Cu, Fe, Li, Mn, Mo, Ni, Pb, Rb, Sb, Se, Sn, Sr, Ti, Tl, U, V, Zn) were determined by high-resolution inductively coupled plasma mass spectrometry (HRICPMS) in the composite samples of raw wastewater and secondary effluent. For the determination of total metals in wastewater samples a novel ultrasonic acid digestion procedure was developed. The observed total and dissolved metal concentrations in raw wastewater were in typical ranges reported for municipal effluents with no indication of a significant industrial input [1]. Due to the high suspended solid load and organic matter content in the raw wastewater, only few of the determined metals were present predominately in the dissolved form (Li, Rb, Sr, U, Se). The majority of metals were partly (Mo, Sb, Cs, As, Ba, Ni, V, Co, Sn, Zn) or nearly completely (Zn, Cr, Tl, Cd, Cu, Pb, Ag, Ti, Fe, Bi, Al) bound to particles. High affinity of these metals for particulate matter is the main mechanism controlling the efficiency of their removal in wastewater treatment. Removal of the most toxic metals (Cr, Cd, Cu, Pb, Ag or Bi) in the investigated WWTP is higher than 85%, but for some other toxic elements, such as As, Sb, Ni, V and Zn, the removal is significantly lower (50- 70%). Due to the much lower particle load, the relative percentage of dissolved metals in secondary effluents (40-100 % for all measured elements) is much higher than in the raw wastewater. For most of the elements (with exception of Zn, Pb and Ag) the concentrations of the dissolved species in secondary effluents were found to be of the same order of magnitude as their concentrations in the Sava River water, indicating that the contribution of the effluents from WWTP of the city of Zagreb to the total metals fluxes in the Sava River was probably not very high.

metals ; municipal wastewater ; Sava River ; dissolved ; particulate

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