Performance and kinetic evaluation of a semi-continuously fed anaerobic digester treating food waste: effect of trace elements on the digester recovery and stability.

This study investigated the effects of trace elements (TEs: Fe, Co, and Ni) on the anaerobic digestion of food waste in laboratory scale semi-continuously fed anaerobic digesters. The digesters were operated for approximately 460 d at organic loading rates (OLRs) ranging from 1.0 to 5.0 g VS L(-1)d(-1) at 37°C. Results showed that methane production was severely inhibited when volatile fatty acids (VFAs) concentration was 30,000 mg L(-1) at OLR of 4.0 g VS L(-1)d(-1) without the addition of TEs. However, the inhibition was gradually decreased and the methane production increased from 0.13 up to 0.44 L g(-1)VS added when the TEs was added. Fe was proved to be the essential element in maintaining the stability of the digester. The conversion coefficient of substrate into biogas (YS/G) was 1.00 and 1.26 gVS removedL(-1) biogas with and without TEs addition, respectively. The estimated biomass yield with feeding TEs (0.06 g VSS g(-1)COD removed) was higher three times than that without TEs (0.02 gVSS g(-1)COD removed).