Department Process Engineering

Eawag; AWEL (Amt für Wasser, Abfall, Energie und Luft)

Rare earth elements (REE) include the lanthanides (La–Lu) as well as scandium (Sc) and yttrium (Y). However, the lanthanides alone are often referred to as REE. In this project, the term “lanthanides” is used synonymously with REE. REE are essential for numerous modern technologies and are therefore in high demand. They typically have similar atomic radii and an oxidation state of +3, with the exceptions of europium (+2/+3) and cerium (+3/+4). As a result, REE display very similar geochemical behavior, which produces characteristic REE patterns in the bedrock.

However, slight differences in the behavior of REE during rock weathering lead to fractionation, with light REE tending to be particle-bound and heavy REE tending to be dissolved (Sholkovitz 1995). In remote areas, REE patterns in watercourses are determined by water chemistry parameters (pH, DOC content, carbonate, sulfate and phosphate concentrations) and the geology of the subsoil (Andersson et al. 2006; Johannesson et al. 1995). Natural REE patterns can be modified by anthropogenic inputs, e.g., from sewage treatment plant discharges.

Based on characteristic REE patterns in wastewater sludge, or changes therein, anthropogenic inputs of specific REEs into various wastewater treatment plants could be identified and quantified (Kaegi et al. 2021). The study does not investigate the extent to which the patterns of REE in wastewater sludge are also found in treated wastewater and whether the inputs from wastewater treatment plants are also visible in watercourses.

Selected watercourses (~70) and discharges from wastewater treatment plants (~60) are sampled by AWEL.