Life cycle assessment of volatile fatty acids production from protein- and carbohydrate-rich organic wastes.

Volatile fatty acids (VFAs) are platform molecules with numerous applications. They can be obtained by adjusting the operational conditions of anaerobic digestion to avoid methanogenesis while focusing on fermentative stages. There are gaps in the knowledge of how, from a life-cycle perspective, the fermentative process performs in VFAs production from waste, including environmental consequences of substituting common commodities in the current market. Mass and energy balances of VFAs production from protein-rich microalgal and carbohydrate-rich agro-industrial wastes were used herein as a key source of inventory data for life cycle assessment. Two waste treatment options were considered: (i) VFAs production (anaerobic fermentation) plus anaerobic digestion of the resulting waste after VFAs separation, and (ii) anaerobic digestion of the original waste for bioenergy. Several scenarios were formulated to evaluate their life-cycle performance. VFAs production generally shows a better environmental behaviour than conventional anaerobic digestion, principally due to the substitution of conventional chemicals.