Effect of zero-valent iron particle size on alleviating acid stress in anaerobic digestion of food waste

Abstract

This work evaluated the effect of zero-valent iron (ZVI) particle size (150 μm-100 nm) on the performance of food waste anaerobic digestion (AD) under various acid stress conditions. The results indicated that ZVI significantly improved the AD performance, ensuring successful CH₄ production even under high acid stress. However, the extent of this promoting effect was highly dependent on the particle size. Nano-scale ZVI (nZVI) demonstrated superior performance in the AD process in terms of CH₄ yield and CH₄ production rate compared to micro-scale ZVI (mZVI). Specifically, the CH₄ yield in the nZVI reactor was 8.24-8.68% higher than that in the mZVI reactor. This improvement was attributed to nZVI's more effective up-regulatory effect on hydrolase activity, as the activities of protease and α-amylase in nZVI reactors were 44.55%-48.54% and 14.65%-77.52% higher, respectively, than those in mZVI reactors. Furthermore, the methanogenic lag phase and maximum CH₄ production rate in the nZVI reactor were 41.64%-49.69% shorter and 9.71-37.69% higher than those in the mZVI reactor, respectively. This can be attributed to nZVI's enhanced promoting effect on the activity of coenzyme 420, Syntrophomonas and Methanosarcina, thereby accelerating the CH₄ production.

Keywords: Anaerobic digestion; Bioenergy; Food waste; Particle size; Zero-valent iron.