Biochar derived from biowaste represents a sustainable and multifunctional material for wastewater treatment, enabling simultaneous waste valorisation and pollutant removal in wastewater. Unlike prior reviews that broadly describe biochar applications, this review provides a focused critical analysis of sewage sludge derived biochar through identifying specific research gaps such as the lack of quantitative meta-analyses, inconsistent reporting of adsorption mechanisms and limited evaluation of toxic metal leaching risks. The study examines production methods such as pyrolysis, hydrothermal carbonization, gasification and their direct influence on biochar properties. Removal efficiencies reported across studies are highly variable with heavy metal removal efficiencies of 60–80% and nutrient removal of 40–75%, but these values lack standardized conditions such as pH, dosage and contact time, limiting cross study comparison. The dominant adsorption mechanisms shift from electrostatic attraction and surface complexation at near-neutral pH to precipitation and ion exchange at alkaline pH. However, quantitative distinctions between physical adsorption and chemisorption are rarely provided. Ash content in sewage sludge biochar enhances phosphate precipitation but can also leach trace metals for example copper and zinc under acidic conditions. Biochar applications improve water clarity and reduce odour, but critical limitations including potential metal leaching, pressure drop in filtration systems and lack of regulatory approval are underexplored. This review concludes that while sewage sludge biochar supports circular economy goals, its large-scale adoption requires standardized production protocols, long term ecological impact studies and comparative techno-economic assessments against activated carbon.
Kampila et al. (Wed,) studied this question.