Anaerobic co-digestion of solid waste: Effect of increasing organic loading rates and characterization of the solubilised organic matter

► Co-digestion of waste studied at a low OLR of <2 kgVS/m3 d yielded 0.33 l CH4/gVS fed. ► OLR increase to a maximum of 7.5 kgVS/m3 d resulted in 20% decrease in methane yield. ► COD solubilised at high loading was characterized for biodegradability and size-fractionation. ► Biodegradability of the solubilised organic matter ranged between 10% and 38%. ► Solubilised COD comprised mostly (82%) of colloidal and very fine particulate organics.