Full scale thermophilic anaerobic digestion of sludge: Effect of co-digestion with agro-industrial wastes [Digestión anaerobia termófila de fangos a escala industrial: Efecto de la co-digestión con residuos agroalimentarios]

A full scale (2500 m 3) 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-diges tion 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 mak ing the waste management less costly and more envi ronmentally sound. Indeed, biogas flow rate remained quasi constant (1678 ± 99 and 1623 ± 147 m 3/day (stan dard temperature and pressure, i.e. 0°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 con firmed the good performance under thermophilic condi tions. 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.