Effects of Fe-modified digestate hydrochar at different hydrothermal temperatures on anaerobic digestion of swine manure

Hydrothermal carbonization temperature is a key factor in controlling the physico-chemical properties of hydrochar and affecting its function. In this study, effects of hydrochar and Fe-modified hydrochar (Fe-HC) prepared at 180 °C (180C-Fe), 220 °C (220C-Fe) and 260 °C (260C-Fe) on anaerobic digestion (AD) performance of swine manure was investigated. Among the three Fe-HCs, 220C-Fe had the highest amount of Fe and Fe2+ on the surface. The relative methane production of control reached 174 %-189 % in the 180C-Fe and 220C-Fe treatments between days 11 and 12. The degradation efficiency of swine manure was highest in the 220C-Fe treatment (61.3 %), which was 14.8 % higher than in the control. Fe-HC could act as an electron shuttle, stimulate the coenzyme F420 formation, increase the relative abundance of Methanosarcina and promote electron transport for acetotrophic methanogenesis in the AD. These findings are helpful for designing an efficient process for treating swine manure and utilizing digestate.