A study by researchers at the University of Auckland in New Zealand and James Cook University in Australia has found that anaerobic co-digestion of textile waste with food waste can substantially increase methane production, offering a dual benefit of renewable energy generation and waste diversion. The research, published (DOI: 10.1007/s42768-026-00316-y) in Waste Disposal & Sustainable Energy, addresses a pressing environmental challenge: approximately 92 million tonnes of textile waste are disposed of annually, with landfilling, incineration, and recycling remaining costly or environmentally problematic.
The significance of the findings lies in the scale of the waste problem and the limitations of current disposal methods. Textile waste is difficult to digest alone due to imbalanced carbon-to-nitrogen (C/N) ratios, recalcitrant keratin in wool, and non-biodegradable polyester in blended fabrics. These materials can slow hydrolysis, cause acidification or ammonia inhibition, and reduce methane output. Food waste, by contrast, is highly biodegradable and nutrient-rich, making it an effective co-substrate. The study systematically evaluated mono- and co-digestion of cotton, polycotton, and wool with food waste under mesophilic conditions, testing substrate-to-inoculum (S/I) ratios of 0.5 and 1 and multiple feedstock mixing ratios.
Results showed that methane yields increased as the S/I ratio decreased. Cotton performed best in mono-digestion, producing 103 mL/g volatile solids (VS) and reaching 25.87% biodegradability at an S/I ratio of 0.5. Co-digestion with food waste generally raised methane production, with the highest yield of 129.7 mL/g VS achieved from a cotton-to-wool ratio of 6:1, which had a balanced C/N ratio of 20.63. Synergy was strongest when food waste made up more than 80% of the blend, especially with cotton, where the co-digestion performance index (C1) exceeded 1. Kinetic analysis using a modified Gompertz model showed that higher food waste shares shortened lag phases and accelerated biogas production. For instance, a 1:4 cotton-to-food-waste blend reached 111 mL/g VS and about 29% methane content, while a 1:1 wool-to-food-waste blend produced almost no methane because of ammonia inhibition.
Polycotton and wool exhibited antagonistic effects (C1 < 1). Polyester, or polyethylene terephthalate (PET), resisted degradation, while wool's keratin structure limited microbial access. Post-digestion analyses linked poor performance to residual volatile fatty acids, soluble chemical oxygen demand, and free ammonia nitrogen above inhibitory thresholds. The authors concluded that co-digestion is most effective when food waste dominates the blend and the C/N ratio stays within the optimal window. Cotton-rich mixtures were especially promising, while polycotton and wool require pretreatment or fiber separation because polyester and keratin resist microbial breakdown.
For textile manufacturers, waste managers, and biogas operators, the study suggests that co-digesting textile waste with food waste can improve methane yields, stabilize digesters, and divert waste from landfill. The best results came from optimizing the S/I ratio and C/N balance, particularly when food waste exceeded 80% of the feedstock. Pretreatment strategies such as thermal hydrolysis for cotton and wool, and environmentally friendly solvents to separate polyester from blended fabrics, could further improve digestibility. Digestate quality also matters: most co-digestion treatments produced free ammonia nitrogen within safe biofertilizer limits, although polycotton and wool blends exceeded inhibitory thresholds for anaerobic digestion. The findings provide a practical screening tool and operating principle for scaling up co-digestion systems, with implications for reducing the environmental burden of textile waste while producing renewable energy.
