Quantification of Element Fluxes in Wastewaters: A Nationwide Survey in Switzerland

Abstract

The number and quantities of trace elements used in industry, (high-tech) consumer products, and medicine are rapidly increasing, but the resulting emissions and waste streams are largely unknown. We assessed the concentrations of 69 elements in digested sewage sludge and effluent samples from 64 municipal wastewater treatment plants as well as in major rivers in Switzerland. This data set, representative of an entire industrialized country, presents a reference point for current element concentrations, average per-capita fluxes, loads discharged to surface waters, and economic waste-stream values. The spatial distribution of many individual elements could be attributed either to predominant geogenic or to anthropogenic inputs. Per-capita element fluxes ranged from <10 μg day (e.g., Au, In, and Lu) to >1 mg day (e.g., Zn, Sc, Y, Nb, and Gd) and >1 g day (e.g., for P, Fe, and S). Effluent loads of some elements contributed significantly to riverine budgets (e.g., 24% for Zn, 50% for P, and 83% for Gd), indicating large anthropogenic inputs via the wastewater stream. At various locations, precious metal concentrations in sludge were similar to those in profitable mining ores, with total flux values of up to 6.8 USD per capita per year or 15 USD per metric ton of dry sludge.

An Overview of Rare Earth Elements in Sewage Sludges and Their Ashes

“…Some data used in this paper were obtained from (1) published articles and (2) new data from our own analysis. The sludges are from Japan [2,3], the USA [1,4], Switzerland [5], Sweden [6], China [7] and Spain (new data). The Japanese sludges came from 14 different wastewater treatment plants (WWTPs) [2], whilst the one studied by Gao et al [3] come from an industrial WWTP.…”

“…The Japanese sludges came from 14 different wastewater treatment plants (WWTPs) [2], whilst the one studied by Gao et al [3] come from an industrial WWTP. Vriens et al [5] analysed sludges from 64 municipal and industrial WWTP located in Switzerland. On the other hand, Verplanck et al [4] and Westerhoff et al [1] studied sewage sludges from several plants sited in the USA, 1 and 96 WWTPs, respectively.…”

“…REY in the ashes and sludges were analysed by inductively coupled plasma-mass spectrometry (ICP-MS) and ICP-atomic emission spectrometry (ICP-AES) after samples acid digestion with HClO4-HNO3-HCl-HF. Figure 1a shows the mean REY concentrations of the sludges from several authors' research [1][2][3][4][5][6][7] and those of the sewage sludges from Spain. REY concentrations show approximately the same pattern, independently of the country of origin ( Figure 1a).…”

“…Sludges [2] Sludge [3] Sludge [4] Sludges [1] Sludges [5] Sludges [6] Sludges [7] Sludge S1 Sludge S2 Sludge S3 0.0 0.5 The highest relative concentrations compared to those in the UCC are reached for Sc in the Chinese sludge [7] and Gd for the industrial sludge [3]. These relative concentrations (REY concentration in the sludge/REY concentration in the UCC) are 1.8 and 2.3, respectively.…”

“…Although there are scarce published data about the concentrations of rare earth elements (lanthanides) plus scandium (Sc) and yttrium (Y) (REY) in sewage sludges and their ashes [1][2][3][4][5][6][7][8][9][10], data show that sludges contain REY. There is no consensus about the interest of recovering REY from sewage sludge and its ashes.…”