Abrogating the inhibitory effects of volatile fatty acids and ammonia in overloaded food waste anaerobic digesters via the supplementation of nano-zero valent iron modified biochar

Ee Yang Lim^a, Jonathan Tian En Lee^b,c, Le Zhang^b,c, Hailin Tian^b,c, Kok Chung Ong^a, Zhi Kai Tio^a

Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, S117576, Singapore.

The effects of different recovery strategies on inhibited anaerobic digestion (AD) of food waste (FW) was examined in this study, with the finding that dosing pine woodchip biochar could reverse the effect of volatile fatty acids (VFA) inhibition (mainly propionic acid) and yielded 105.55% more methane than the control. The addition of nano-zerovalent iron (nZVI) promoted the generation of VFA while causing a slight inhibition of the methanogens initially. In due time, the nZVI digester was able to recover and eventually produced 192.22% more methane compared to the control. Finally, nZVI-modified biochar was proved to be able to avoid the inhibitory effects brought about by the nanoparticles. The results indicated reduced dosage requirements as compared to using pristine pine woodchip biochar and accumulated 204.84% more methane than the control. The introduction of nZVI-biochar also promoted the growth of Methanosarcina species methanogens, which can perform direct-interspecies electron transfer. While all the recovery strategies using the additives were feasible, the results suggested that the use of modified biochar holds great potential as a significantly lower amount of amendment is required for the recovery of the inhibited AD system.

Keywords: Biogas, Food waste, Woodchip biochar, Zero valent iron, Recovery of anaerobic digestion.