Fate and effects of emerging contaminants during anaerobic digestion of organic wastes: Effective exposure, mechanisms and intervention strategies.

Abstract

Methane recovery from anaerobic digestion can be held back by emerging contaminants, and so can the range of uses open to the digestate. This review covers pharmaceuticals, disinfectants, per- and polyfluoroalkyl substances, micro- and nanoplastics, and selected engineered nanomaterials in sludge, manure, food waste, and industrial residues. The synthesis draws on comparisons within individual studies to examine how contaminant form, contact with biomass, and exposure duration shape responses at individual steps of anaerobic digestion. Reversals between stimulation and inhibition appear in dose series for perfluorobutanesulfonate and for bisphenol A. Inhibition can also emerge once exposure is prolonged, at a point that short-term tests do not reach. Among the interventions examined, gains in methane recovery do not necessarily coincide with gains in contaminant transformation or in antibiotic-resistance outcomes. Two separate tasks are involved: restoring inhibited digestion, and improving contaminant transformation without losing methane production. Products left behind by transformation can retain biological activity. Phase-resolved mass balances are a way to tell genuine destruction apart from transfer into concentrates and spent media. Engineering comparisons show that a benefit can fade even when the material is still in place, and that a higher electrical input can return less additional methane. Intervention selection should account for the limiting conversion step, the residues relevant to the intended use of digestate, and the energy, materials and maintenance needed to sustain treatment.

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