Agricultural Use of Sewage Sludge as a Threat of Microplastic (MP) Spread in the Environment and the Role of Governance

Abstract

Sewage sludge from wastewater treatment plants is commonly used as a soil amendment on agricultural land. Unfortunately, more and more research indicates that large amounts of microplastic (MP) are re-introduced to soil with sludge. This study aims to present the impact MP has on soil ecosystems, global trends in agricultural sludge management resulting from a high concentration of micropollutants in sludge, and finally propose a high-level strategy for sustainable sludge management. This strategy is mostly dedicated to the European Union and involves multiple stakeholders and the links between each of them to achieve appropriate sludge management to avoid soil pollution with MP. Governance, Technology, Consumer Acceptance, and Economy and Commercial Viability is explored in depth. To the author's knowledge, this is the first paper to discuss these topics in the context of a changing agricultural scene and identifies ways of which sewage sludge can limit MP pollution whilst still fitting into a circular economy. As total elimination of agriculturally used sludge is not a viable option, more stringent regulation on sludge quality before its use is necessary, especially on contaminant concentrations. This includes MPs limits, to improve sludge quality, in turn improving soil health. More alternative management options for sludge that does not meet land usage requirements are necessary and will be explored in this study. Overall, the combination of factors discussed will inevitably lead to more emphasis on sewage sludge management, therefore it can be expected that the information presented in this review will be of high demand and importance for sludge producers and serves as a comprehensive foundation for researchers to build off.

The Burden of Microplastics Pollution and Contending Policies and Regulations

“…EU countries have recognized sewage sludge (SS) as a major factor contributing to the contamination of agricultural land, and this has led it to formulate high-level strategy for sustainable SS management by its member countries. The strategy involves multiple stakeholders being expected to work harmoniously to achieve the desired goal of appropriate and efficient management [ 58 ]. It requires a review of directive 86/278/EEC on SS that will recognize the relationship between sewage and MPs, as well strictly prohibiting SS disposal on land unless necessary.…”

“…It requires a review of directive 86/278/EEC on SS that will recognize the relationship between sewage and MPs, as well strictly prohibiting SS disposal on land unless necessary. Additionally, it requires plans to actualize a circular economy and provide alternatives to SS handling through high tech processes in waste water sewage plant to be strengthened by research and development [ 58 ].…”

Entrained Flow Plasma Gasification of Sewage Sludge–Proof-of-Concept and Fate of Inorganics

“…Agricultural application is also limited by the permissible limits on heavy metal content, i.e., 20 mg/kgdry of Cd, 1000 mg/kgdry of Cu, 16 mg/kgdry of Hg, 300 mg/kgdry of Ni, 750 mg/kgdry of Pb, and 2500 mg/kgdry of Zn, as specified in European Council Directive 86/278/EEC [30]. For agricultural use, the threat of microplastics should also be taken into serious consideration [31]. The following regulations are important on the EU level [26,27 Conversion of solid fuel to gas is the main point of gasification [32,33].…”

Reuse of Water Contaminated by Microplastics, the Effectiveness of Filtration Processes: A Review

“…This implies that most of the MPs removed during wastewater treatment will end up in the open environment [33,61]. For this reason, Wolff et al [62] indicated that WWTPs are a good sink for MPs only when the sludge is thermally treated and not used for agricultural amendment.…”