Optimising Volatile Fatty Acid Production from Organic Waste: Effect of Organic Load and Zeolite Addition on Acidogenesis and Ammonia

The production of volatile fatty acids (VFA) through acidogenic fermentation of organic waste is a promising strategy for resource recovery in circular bioeconomy systems, especially in those conditions where efficient resource utilisation is imperative, such as in future lunar missions. In this study, in collaboration with the Italian Space Agency, the organic waste conversion was investigated to produce VFA-rich effluent obtained under optimal conditions represents a promising potential feedstock for future downstream applications, such as photofermentative hydrogen production, although downstream biological validation was beyond the scope of the present study. In this experimental work, a synthetic mixture of organic waste and waste-activated sludge was fermented across varying organic loads (20–50 gTVS/L) with and without zeolite, supplemented as an ammonium absorbent. Results showed that VFA production increased with organic loads, with the highest volatile fatty acid yields observed at 40 gVS/L. Keeping the organic loads constant at 40 gVS/L, zeolite addition further enhanced volatile fatty acid concentrations in a dose-dependent manner, reaching a maximum at 15 g/L and 20 g/L; the highest yield was obtained at 30 and 40 gVS/L with 15 g/L, reaching a peak of 0.8 gCOD/gVS. Zeolite addition reduced the ammonia conversion by about 6% at OL 40 and 50.