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From Waste to Fertilizer or Soil Amendment: a Performance-based Critical Review of Agronomic Effectiveness, Safety, Processing, and Circular-economy Readiness
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This review of recent studies looks at turning waste, like sewage sludge and food scraps, into fertilizer. Some recycled products, like struvite, work reliably as plant food, but others carry risks: heavy metals, pathogens, microplastics, and radioactive contaminants that could end up in soil, crops, and eventually our food and health. More testing and clearer safety rules are needed before these products are widely trusted.
Waste-derived fertilizers and soil amendments are increasingly proposed as responses to fertilizer supply risk, waste-disposal pressure, and the environmental burdens of conventional nutrient production. This structured critical review evaluates evidence published from January 2020 through August 2026 on the conversion and agricultural use of municipal, agro-industrial, industrial, mining, metallurgical, and construction-associated residues. The review compares biosolids and composts, digestates, recovered ammonium products, struvite and other recycled phosphorus salts, sewage-sludge ash, biochar and hydrochar, organomineral formulations, steel slag, phosphogypsum, rock powders, and construction-derived mineral fines. A performance-first framework separates total nutrient content from plant-available nutrient delivery and distinguishes defined fertilizers, hybrid fertilizers, and soil amendments or remineralizers. Evidence is appraised separately for agronomic effectiveness, safety, process maturity, product engineering, and techno-economic/life-cycle robustness, so that field performance is not conflated with technology scale. The strongest direct-fertilizer evidence is associated with compositionally defined recovered nutrients, particularly struvite and selected recycled nutrient salts, whereas standardized digestate fractions and organomineral products show conditional readiness that depends on composition control and management. Mineral residues and construction-derived fines generally function more defensibly as liming, calcium, magnesium, silicon, sulfur, or remineralizing amendments unless plant-available nutrient delivery is demonstrated. Across product classes, decisive constraints include nutrient speciation and release kinetics, feedstock variability, metals and emerging contaminants, pathogens, microplastics, source-specific radionuclides, product handling, long-term accumulation, and inconsistent analytical and regulatory frameworks. The review proposes an ordinal, evidence-based readiness framework and identifies priorities for multi-season field validation, standardized nutrient-availability testing, contaminant bioavailability, manufacturing quality assurance, predictive modeling, and full-scale integration.
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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.
Situating the discourse of recycled nutrient fertilizers in circular economy principles for sustainable agriculture
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This review examines the integration of recycled nutrient fertilizers into sustainable agriculture within a circular economy framework, highlighting concerns about contaminants including microplastics, toxic elements, and antibiotic resistance genes. Researchers found that technologies like struvite precipitation and biochar production show promise but face challenges with cost and contamination risks. The study emphasizes that supportive policies, market incentives, and public education are essential for broader adoption of recycled fertilizer products.
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.
Wastewater recovered struvite: Quality assessment for heavy metals, PFAS, and microplastic
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Researchers assessed struvite — a phosphorus-rich fertilizer recovered from sewage — for contamination with heavy metals, PFAS (forever chemicals), and microplastics, finding that struvite produced in industrial wastewater equipment can exceed safe heavy metal limits. The findings raise concerns about whether recycled fertilizers could introduce pollutants into agricultural soils.
Microplastics in Waste-Derived Fertilisers
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Fertilizers made from sewage sludge, compost, and food waste help recycle nutrients back into farm soil, but this review of existing research shows they can also introduce microplastics into the ground where our food grows. Current EU rules only restrict larger plastic pieces (bigger than 2mm), leaving smaller microplastic fragments largely unregulated and understudied—meaning scientists still don't know how much of this plastic ends up in crops or what it means for the food on our plates. The researchers say better, standardized testing is urgently needed to understand the real risks before we can say how worried we should be.
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