Non-labile silver species in biosolids remain stable throughout 50 years of weathering and ageing

This paper reports the speciation and lability of Ag in archived, stockpiled, and contemporary biosolids from the UK, USA and Australia, and indicates that biosolids Ag concentrations have decreased significantly over recent decades

E. Donner

2015

Scholarcy highlights

  • Silver has been used by humans for millennia; as a precious metal and symbol of wealth, and in applications as diverse as sanitation, photography, industrial catalysis, dentistry, and healthcare
  • X-ray Absorption Near Edge Spectroscopy revealed the importance of reduced-sulfur binding environments for Ag speciation in materials ranging from freshly produced sludge to biosolids weathered under ambient environmental conditions for more than 50 years
  • , the photographic uses of silver in the USA, Japan, and Western Europe accounted for 40% of the total global Ag demand but this declined significantly due to the subsequent rise of digital photography
  • Material use patterns are never static and the declining use of Ag in the photographic sector has been accompanied by an increase in other uses; including some which are likely to result in inadvertent wastewater release
  • This paper presents an overview of biosolids Ag chemistry in historic and contemporary biosolids sourced from the UK, USA and Australia from the 1950s until today by drawing on a unique collection of archived, stockpiled and contemporary biosolids samples
  • Other minor species identified here included elemental Ag, and Ag bound to organic ligands. It should be noted, that as uncertainty in species apportionment is estimated to be approximately 10% of the total amount of the target element, values less than 10% should be considered with caution
  • These results clearly demonstrate that the reduced-sulfur-Ag species in biosolids are extremely stable over time, with Linear Combination Fitting indicating this form to account for at least 77 % of the average Ag speciation in all 6 samples, despite them having been exposed to extended weathering
  • Despite the wide range of dispersive commercial and industrial uses that contribute to wastewater Ag loads, and the variety of biosolids processing and storage scenarios, the presented data strongly support previous reports that Ag undergoes strong sulfidation reactions in wastewater; and uniquely, these data confirm that the reduced sulfur species formed during treatment remain stable despite extensive weathering over multiple decades

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