Effect of seaweed addition on enhanced anaerobic digestion of food waste and sewage sludge

To investigate the effect of seaweed (SW) addition on anaerobic co-digestion of food waste (FW) and sewage sludge (SS), batch experiments were conducted at various substrate concentrations (2.5, 5.0, 7.5, and 10.0 g volatile solids (VS)/L) and mixing ratios ((FW or SS):SW = 100:0, 75:25, 50:50, 25:75, and 0:100 on a VS basis). The effect of SW addition on FW digestion was negligible at low substrate concentration, while it was substantial at high substrate concentrations by balancing the rate of acidogenesis and methanogenesis. At 10 g VS/L, CH₄ production yield was increased from 103 to 350 mL CH₄/g VS by SW addition (FW:SW = 75:25). On the other hand, SW addition to SS enhanced the digestion performance at all substrate concentrations, by providing easily biodegradable organics, which promoted the hydrolysis of SS. k_hyd (hydrolysis constant) value was increased from 0.19 to 0.28 d^-1 by SW addition. The calculation showed that the synergistic CH₄ production increment by co-digesting with SW accounted for up to 24% and 20% of total amount of CH₄ production in digesting FW and SS, respectively.