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Variation in microplastic concentration, characteristics and distribution in sewage sludge & biosolids around the world
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Researchers systematically reviewed 65 studies on microplastics in sewage sludge and biosolids from wastewater treatment plants around the world. They found that while treatment processes remove 57% to 99% of microplastics from wastewater, the removed particles concentrate in sludge that is often applied to agricultural land. The review highlights that land application of biosolids may be a significant, underappreciated pathway for microplastic pollution in soils.
Microplastics have been reported in wastewater treatment works across the world. The majority of microplastics are removed during the wastewater treatment process, with removal efficiencies between 57 % to 99 %. What happens to the microplastics removed from the wastewater, and how they accumulate in sewage sludge and biosolids (by-products of the wastewater treatment process), remains a topic of high interest. Here we systematically reviewed the current state of knowledge on the presence, concentration, and characteristics of microplastics in sewage sludge and biosolids globally to understand how biosolids may act as a pathway for microplastic pollution to soils. A systematic search was performed on the Web of Science and Science Direct databases. Sixty-five studies reporting on microplastic pollution in sewage sludge and biosolid products were identified, spanning twenty-five countries. Reported microplastic concentrations varied considerably from 0.193 microplastics/g to 1.69 × 105 microplastics/g with a median microplastic concentration of 22.41 microplastics/g, illustrating how many microplastics are captured during the wastewater treatment process, and retained in the sewage sludge. The extent to which biosolid recycling pollutes the terrestrial environment was compared between countries. High numbers of microplastics were estimated to reach fields via biosolid application with a wide variation of 8.2 × 1010 to 1.29 × 1015 microplastics/year between sixteen countries, although there was no significant difference in microplastic concentration between fields with a history of biosolid applications and control fields. The comparative risk this delivery of approx. 0.4 to 6430 tonnes of microplastics poses compared to the environmental benefits of nutrient and carbon recycling associated with biosolids reuse, or compared to other sources of microplastic pollution remains a global research imperative. The next step in scientific research needs to focus on solutions to the biosolid and circular economy conundrum - biosolids are a valuable source of nutrients but contain high concentrations of microplastics, which are ultimately entering the terrestrial environment.
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Variation in microplastic concentration, characteristics and distribution in sewage sludge & biosolids around the world
AI summary Read the abstract
This review synthesizes global data on microplastic concentrations, characteristics, and distribution in sewage sludge and biosolids, drawing on studies showing wastewater treatment works remove 57-99% of incoming microplastics, concentrating them in sludge byproducts. The review highlights the significance of this concentration pathway and what happens to these microplastics when sludge is applied to land or otherwise managed.
Investigation and analysis of microplastics in sewage sludge and biosolids: A case study from one wastewater treatment works in the UK
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Researchers investigated microplastic contamination in sewage sludge and biosolids at a UK wastewater treatment plant and found significant quantities of microplastics persisting through the treatment process. Since millions of tonnes of biosolids are applied to farmland annually in the UK, this represents a major pathway for microplastic pollution entering agricultural soils. The study highlights the need for better monitoring and treatment methods to reduce microplastic transfer from wastewater to the terrestrial environment.
Investigation and analysis of microplastics in sewage sludge and biosolids: A case study from one wastewater treatment works in the UK (article)
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This UK case study tracked microplastics through an entire sewage sludge treatment stream at one wastewater works, from raw influent through to biosolids applied to agricultural land. Microplastics were present at every stage and concentrated in biosolids, suggesting land application of biosolids is a significant pathway for introducing microplastics into agricultural soils.
Microplastic removal and management strategies for wastewater treatment plants
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This review examines how well different wastewater treatment technologies remove microplastics and what management strategies can improve performance. While conventional treatment plants can remove a large percentage of microplastics from water, the particles often end up concentrated in sewage sludge that gets applied to farmland. The study highlights the need for advanced treatment options and better management of biosolids to prevent microplastics from simply being transferred from water to soil.
Fate of microplastics in sewage sludge and in agricultural soils
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Researchers reviewed how microplastics accumulate in sewage sludge at wastewater treatment plants and then spread into agricultural soils when that sludge is applied as fertilizer, finding that sludge treatment processes can alter microplastic size and shape but do not eliminate them. The review calls for standardized methods to study how different sludge treatments affect microplastic properties and their downstream risks to soil health.
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