Origin and fate of heavy metals in an urban area (Leoben, Austria) as traced by chemical and magnetic investigations of sewage sludge and water

Category Geochemistry
Group GSI.IR
Location International Geological Congress,oslo 2008
Source www.۳۳igc.org
Holding Date 26 August 2008
 

Origin and fate of heavy metals in an urban area (Leoben, Austria) as traced by chemical and magnetic investigations of sewage sludge and water

Rantitsch, Gerd; Gaisberger, Elisabeth; Scholger, Robert; Windisch, Thomas; Runge, Birgit; Meisel, Thomas; Prochaska, Walter; Gratzer, Reinhard
University of Leoben, Austria


To understand the sources of contaminants to urban particulates, and to predict the mobility and impact of these contaminants in urban systems, detailed geochemical and mineralogical information is needed. Integrated geochemical and mineralogical analysis of urban particle composition has not been thoroughly pursued, and the fate of such sediments in the urban environment is not well archived. Therefore, the understanding of the sources, environmental reactivity and the overall impact of urban sediments on both health and the environment is limited. This gives the motivation to investigate the accumulation and dispersion of heavy metals during the wastewater treatment process in a wastewater treatment plant of a regional urban centre (Leoben, Austria), which includes also an input from small enterprises and industrial sources.
Metal concentrations were measured by ICP-MS and AAS, both in the influent and the effluent water, as well as in the dewatered sludge. Some selected sludge samples were characterized by organic geochemical methods (GC-MS). Magnetic characterizations of the mineral phases were carried out on selected samples. Mineralogical examinations were performed by reflected-light microscopy, scanning electron microscopy and microprobe analysis. The results suggest that the heavy metal accumulation during the wastewater treatment process is controlled by anthropogenic and industrial processes in the hinterland of the wastewater treatment plant. Organic geochemical studies of sewage sludge samples detect the contribution of lubricants, tensides and residuents from the forest industry. A sequential chemical extraction assesses the bioavailability of pollutants in sewage sludge. The results demonstrate that the elements Cr, Ni, and Pb are bounded in the residual fraction of the sludge and indicate therefore a low degree of bioavailability. The major part of the heavy metal load of the wastewater is bounded to the particulate phase. The distribution of individual metals between the particulate and dissolved phase of the wastewater shows a predominantly particulate binding (>0,2 ìm) for the elements As, Cr, Co, Pb, Sn, Cu, Zn, Sb und Ni in the influents. Lower partition coefficients characterize the effluents. In the influents, the relation between the elemental concentrations and the flow rate suggests a three-component-system, involving the variation of the heavy metal supply, the capability of water to dissolute them, and the flow rate within the wastewater treatment plant. Heavy metals are bounded to the magnetic fraction (prevalently magnetite and hematite) of the individual samples, consisting solely of anthropogenic particles.
The achieved results demonstrate that magnetic analysis in combination with mineralogical and chemical analyses provides a promising way to trace and map the dissipation of heavy metals in an urban environment.