Full Scale Thermophilic Anaerobic Digestion of Sludge: Effect of Co-digestion with Agro-industrial Wastes

A full scale (2500 m) study has been performed to improve waste management in an agro-industrial factory of frozen food, by upgrading the thermophilic anaerobic digestion of sludges (from wastewater treatment) toward co-digestion of sludges and agro-industrial solid wastes (mainly wastage of pre-cooked food). The aim was to minimize the amount of wastes to be treated or disposed of out of the factory and to recover energy from wastes, so making the waste management less costly and more environmentally sound. Indeed, biogas flow rate remained quasi constant (1678 +/- 99 and 1623 +/- 147 m(3)/day (standard temperature and pressure, i.e. 0 degrees C and 1 bar), for digestion and co-digestion, respectively). On another hand, total solids removal yield increased from 58.8 to 65.0% and volatile solids removal yield from 66.9 to 72.8%. Therefore, the addition of agro-industrial wastes confirmed the good performance under thermophilic conditions. By means of multiple linear regression analysis it was possible to predict biogas flow rate and removal yield as a function of various process variables.