Transforming sewage sludge into a safe circular economy agronomic inputs through (co-)composting: Nutrient value, soil-structure benefits, and contaminant control

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.