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Transforming sewage sludge into a safe circular economy agronomic inputs through (co-)composting: Nutrient value, soil-structure benefits, and contaminant control
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Co-composting sewage sludge with carbon-rich bulking agents can produce biofertilizers that improve soil health and crop yields while partially degrading organic contaminants through thermophilic processing. However, the review warns that composting does not eliminate emerging pollutants like microplastics, underscoring the need for upstream source control and enhanced monitoring before sludge-derived products reach agricultural soils.
An urgent management issue and a strategic opportunity for nutrient and organic-carbon recovery are presented by the increasing production of sewage sludge on a global scale due to the expansion of wastewater treatment.An efficient and scalable method for stabilizing sludge, reducing smells and pathogens, and producing a mature product that may be used as a biofertilizer for agriculture and an amendment to soil structure is composting, particularly when combined with carbon-rich, porous co-substrates.In this review, we will look at the most upto-date research on the biochemical and physicochemical changes that lead to humification and nitrogen stabilization, as well as the fundamentals of the processes involved and the roles played by common bulking agents in addressing low porosity, high moisture, and low C/N constraints.There is evidence that organic complexation reduces bioavailable heavy metals, thermophilic hygienization is consistently achieved by well-designed cocomposting, and many residual organic contaminants are partly degraded.When applied at nutrient-balanced rates, mature sludge co-composts provide consistent yield advantages by supplying slow-release nitrogen and durable phosphorus, improving soil organic carbon, aggregation, porosity, and water-holding capacity, and enhancing microbial biomass and enzyme activities.The need for upstream source management and enhanced monitoring is underscored by the fact that composting does not eliminate new pollutants like PFAS and microplastics, which may remain in the end products.With the availability of co-substrates and well-established compost markets, co-composting has the potential to bridge the gap between urban and rural areas in terms of nutrients, while also competing with thermal and disposal options from a techno-economic and life-cycle perspective.This might lead to advantages for the circular economy.Sludge valorization has some theoretical backing in Morocco, however the country's legislation regarding risk-based applications and agricultural quality requirements are lacking.As a result, we can see the country's huge potential as well as its serious governance problems.Integral components of trustworthy agricultural reuse frameworks include control of feedstocks, optimization of processes, certification of products, and monitoring of soil over extended periods of time.This will guarantee progress down the road.
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Assessing and Mitigating Risks of Emerging Contaminants in Fertilizer Production from Sewage Sludge: Challenges and Opportunities
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Treated sewage sludge (basically processed human waste) is increasingly recycled into fertilizer, but this review of existing research finds it can carry hidden risks like heavy metals, disease-causing germs, microplastics, and drug residues that may end up in soil, water, and potentially our food. The good news is that proper treatment methods, like composting or heat processing, can reduce these dangers, but the researchers stress that current regulations have gaps, meaning stronger oversight and monitoring are needed before this "waste-to-fertilizer" approach can be considered fully safe.
How Valuable Are Organic Amendments as Tools for the Phytomanagement of Degraded Soils? The Knowns, Known Unknowns, and Unknowns
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This review evaluates organic soil amendments — including sewage sludge, compost, and manure — as tools for restoring degraded soils, noting both benefits for soil health and risks from contaminant introduction. The discussion is relevant to microplastic research because many organic amendments are known vectors for microplastic contamination in agricultural soils.
The fate of microplastic in sludge management systems
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This review assessed the fate of microplastics in sewage sludge management systems, finding that standard stabilization processes including anaerobic digestion and composting do not substantially reduce MP concentrations. Land application of MP-rich sludge was identified as a major pathway for plastic particles entering agricultural soils, with the review calling for alternative sludge disposal strategies aligned with circular economy principles.
Sewage sludge as a sustainable fertilizer: Promise, pitfalls, and future directions
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This review examines both the promise and pitfalls of using sewage sludge as a fertilizer, finding that while it reduces agrochemical costs and provides nutrients for crops, it also introduces microplastics, pathogens, and heavy metals into agricultural soils with implications for food safety and public health.
Co-composting of sewage sludge as an effective technology for the production of substrates with reduced content of pharmaceutical residues
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Researchers found that co-composting sewage sludge with other materials effectively reduced pharmaceutical residues and made the resulting product safer for agricultural use. While primarily about drug contamination, this is relevant to microplastics because sewage sludge is a major source of microplastics that enter farmland when used as fertilizer. Understanding how composting changes pollutant levels in sludge could help develop treatment methods that reduce both pharmaceutical and microplastic contamination in agricultural soil.
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