Unveiling the role of activated carbon on hydrolysis process in anaerobic digestion.

Conventionally, activated carbon is widely applied in water treatment systems due to its capability of adsorbing inhibitors or stimulating methanogenesis rate. This study demonstrates that powder activated carbon (PAC) also stimulate hydrolysis in anaerobic digestion (AD) of thermal hydrolysis pretreated sludge. This is evidenced with 0.95-1.42 times higher methane generation, 12.46-20.06% higher volatile solids removal and greater refractory compounds degradation stimulated by PAC. Functional prediction reveals that genes coding hydrolytic enzymes and xenobiotics metabolism were highly expressed with the presence of PAC. Furthermore, the stimulated hydrolysis activity was effectively maintained at PAC concentration as low as 0.125 g/L, though methanogenesis rate reduced by 80.30% compared to 1 g/L case. This study reports the role of activated carbon on the hydrolysis which has been ignored previously and the impact of PAC on AD performance in long-term operation. The results improve understanding on the true function of PAC in AD system.