Trace organic contaminants in biosolids: Impact of conventional wastewater and sludge processing technologies and emerging alternatives

• Hydrophobicity, charge and molecular structure influence TrOC accumulation on sludge.
• pH, temperature, solids content, SRT and chemical dosing can affect TrOC fate.
• Aerobic digestion and composting can achieve high TrOC removal from sludge.
• Sludge estrogenicity may increase following anaerobic digestion.
• Advanced oxidation and bioaugmentation may effectively remove TrOC from sludge.

This paper critically reviews the fate of trace organic contaminants (TrOCs) in biosolids, with emphasis on identifying operation conditions that impact the accumulation of TrOCs in sludge during conventional wastewater and sludge treatment and assessing the technologies available for TrOC removal from biosolids. The fate of TrOCs during sludge thickening, stabilisation (e.g. aerobic digestion, anaerobic digestion, alkaline stabilisation, and composting), conditioning, and dewatering is elucidated. Operation pH, sludge retention time (SRT), and temperature have significant impact on the sorption and biodegradation of TrOCs in activated sludge that ends up in the sludge treatment line. Anaerobic digestion may exacerbate the estrogenicity of sludge due to bioconversion to more potent metabolites. Application of advanced oxidation or thermal pre-treatment may minimise TrOCs in biosolids by increasing the bioavailability of TrOCs, converting TrOCs into more biodegradable products, or inducing complete mineralisation of TrOCs. Treatment of sludge by bioaugmentation using various bacteria, yeast, or fungus has the potential to reduce TrOC levels in biosolids.