Co-enhancing effects of zero valent iron and magnetite on anaerobic methanogenesis of food waste at transition temperature (45 °C) and various organic loading rates.

Deoiling of food waste (FW) after hydrothermal pretreatment occurs at high temperatures, and more energy is required for substrate cooling before the anaerobic digestion (AD) process. AD at the transition temperature (for example 45 °C) is good for energy saving and carbon emission reducing when treating deoiling FW. However, the metabolic activity of methanogens must increase at the transition temperatures. This study proposes the use of zero-valent iron (Fe) and magnetite (FeO) to boost CH yield from deoiling FW. The results showed a co-enhancing effect on CH yield upgradation when using Fe and FeO simultaneously, and the highest CH yield reached 536.23 mLCH/gVS, which was 67.5 % higher than that of Fe alone (320.14 mLCH/gVS). In addition, a high organic loading was favorable for increasing the CH yield from deoiling FW. Microbial diversity analysis suggested that the dominant methanogenic pathway at 45 °C was hydrogenotrophic methanogenesis. Herein, a potential metabolic pathway analysis revealed that the co-enhancing effects of Fe and FeO enhanced syntrophic methanogenesis and possibly boosted electron transfer efficiency.