Assessing metal contamination and speciation in sewage sludge: implications for soil application and environmental risk

Abstract

Based on the most recently published data, we definitively estimated that the annual global production of sewage sludge may rise from ~ 53 million tons dry solids currently to ~ 160 million tons if global wastewater were to be treated to a similar level as in the 27 European Union countries/UK. It is widely accepted that the agricultural application is a beneficial way to recycle the abundant organic matter and plant nutrients in sewage sludge. However, land application may need to be limited due to the presence of metals. This work presents a meticulous and systematic review of the sources, concentrations, partitioning, and speciation of metals in sewage sludge in order to determine the impacts of sludge application on metal behavior in soils. It identifies that industrial wastewater, domestic wastewater and urban runoff are main sources of metals in sludge. It shows conventional treatment processes generally result in the partitioning of over 70% of metals from wastewater into primary and secondary sludge. Typically, the order of metal concentrations in sewage sludge is Zn > Cu > Cr ≈ Pb ≈ Ni > Cd. The proportion of these metals that are easily mobilised is highest for Zn and Ni, followed by Cd and Cu, then Pb and Cr. Sludge application to land will lead to elevated metal concentrations, and potentially to short-term changes to the dominant metal species in soils. However, the speciation of sludge-associated metals will change over time due to interactions with plant roots and soil minerals and as organic matter is mineralised by rhizo-microbiome.

Evaluation of the Heavy Metals Content in Sewage Sludge from Selected Rural and Urban Wastewater Treatment Plants in Poland in Terms of Its Suitability for Agricultural Use

“…The analysis showed that the trend of metal concentra- As can be observed, the results varied slightly, but in all cases, Zn and Cu showed the highest concentrations and Cd the lowest. Overall, the distribution pattern found in the WWTPs was similar to that found for sludge produced in other WWTPs [44,[50][51][52].…”

“…Metal concentrations in sludge can vary from country to country, but typical metal concentrations in all countries are similar to those presented in this assessment [9,[51][52][53][54][55][56][57][58][59][60][61]. However, it should be noted that metal concentrations in European and Japanese sludge are generally lower than in sludge from other countries [50].…”

“…Typically, the contaminant metal concentrations in sewage sludge decrease in the order Zn > Cu > Cr ≈ Pb ≈ Ni > Cd [50]. The analysis showed that the trend of metal concentra- As can be observed, the results varied slightly, but in all cases, Zn and Cu showed the highest concentrations and Cd the lowest.…”

A bibliometric perspective on the occurrence and migration of microplastics in soils amended with sewage sludge

“…Globally, wastewater treatment facilities currently generate approximately 53 million tons of dry sewage sludge annually (Feng et al, 2023). If wastewater treatment practices were similar to those in the European Union/the United Kingdom, this sludge output would potentially increase to 160 million tons yearly.…”

Antibiotic Resistance in Metal-Tolerant Microorganisms from Treatment Facilities

“…The release of trace elements, especially heavy metals and metalloids, into the environment as a result of industrial development and urbanization is a global problem today [13]. The main amount of metals comes from industrial wastewater [14]. However, domestic and non-industrial wastewater from industrial enterprises entering municipal wastewater treatment plants may also contain significant amounts of trace elements.…”