Anaerobic co-digestion of source selected organic fraction of municipal solid waste and wastewater treatment plant sludge

The possibility of co-digestion of Wastewater Treatment Plant sludge together with the source sorted organic fraction of municipal solid waste, in the frame of an integrated approach for municipal waste management, was considered in reference to the metropolitan area of Florence (Italy). The source sorted organic fraction of municipal solid waste available from the collection system is of different types and quality, highlighting, in any case, the presence of undesirable materials. In order to feed these organic streams to the anaerobic digesters of the Wastewater Treatment Plant for co-digestion process, a pre-treatment aimed to remove the undesirable materials is required. Two typologies of pre-treatments were considered, characterised by different yields in the organic output. Biogas production in co-digestion process was estimated by applying the ADM1 model. With respect to the conventional situation of only sludge digestion, a significant increment of biogas production was registered in all the codigestion scenarios, as expected. Consequently it was checked that also from an overall energy balance point of view, the co-digestion process offers benefits, which increase as the amount of the organic fraction increases.