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Risk of re-release of microplastics from sewage fertilisers into the environment
Summary
This paper reviews the risk that microplastics in sewage sludge (biosolids used as agricultural fertilizer) will be re-released into soils and water when the sludge is land-applied. Microplastics from cosmetics and clothing fibers concentrate in sludge during wastewater treatment and persist because they resist biodegradation. Applying microplastic-contaminated biosolids to farmland is one of the major pathways through which microplastics enter agricultural soils.
Microplastics found in sewage are mainly microparticles from cosmetics (peelings, toothpaste) and fibres from fabrics (which get into the sewage during washing). Microplastics removed from wastewater accumulate primarily in raw sludge, which it ends up in the sludge processing sector. Due to their low susceptibility to biodegradation, microplastics together with stabilised sewage sludge end up in the soil or are otherwise processed together with the sludge.The purpose of the research was to analyze the content of microplastics in stabilised sewage sludge, of which up to 90% is used to produce fertilizers. The analysis was based first on the oxidation of the matrix with peroxide and then density separation with a saturated solution of zinc chloride (ZnCl2). The second stage consisted of the analysis of separated microplastic fractions. For this purpose, the ATR FTIR and FTIR microscope were used. A complementary apparatus was also used, which was a confocal Raman microscope. Stabilised sewage sludge was analyzed depending on the day of its collection. The highest amount of microplastics was found in the samples from Monday, Friday and Saturday. This was due to the increased release of hygiene products containing plastic microbeads. Qualitative analysis, which showed the highest amount of LDPE microplastic fraction. The highest amount of microplastics per 100 grammes of dry weight was 1,084 fragments and 1,128 fibres, for a total of 2,212 microplastic particles. If 90% of the stabilised sewage sludge was used for the production of fertiliser, the emission would be about 1990 particles per 100 grammes. The study showed that the use of sewage sludge to create fertilisers will contribute to the emission of a significant amount of microplastics into the environment. Acknowledgments: A Research project financed by program “Initiative for Excellence – ResearchUniversity” for the AGH University of Science and Technology. The research was supported byResearch Subsidy AGH 16.16.210.476.
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