RESUMO
Biohythane production through one-stage anaerobic digestion of sulfate-rich hydrolyzed tofu processing residue has been hampered by high H2S production. Herein, two-stage anaerobic digestion was investigated with the addition of molybdate (MoO42-; 0.24-3.63 g/L) and ferric chloride (FeCl3; 0.025-5.4 g/L) to the dark fermentation stage (DF) to improve biohythane production. DF supplemented with 1.21 g/L MoO42- increased hydrogen yield by 14.6% over the control (68.39 ml/g-VSfed), while FeCl3 had no effect. Furthermore, the maximum methane yields of methanogenic fermentation were 524.8 and 521.6 ml/g-VSfed with 3.63 g/L MoO42- and 0.6 g/L FeCl3 compared to 466.07 ml/g-VSfed of the control. The maximum yields of biohythane and energy were 796.7 ml/g-VSfed and 21.8 MJ/kg-VSfed with 0.6 g/L FeCl3 when the sulfate removal efficiency was 66.7%, and H2S content was limited at 0.08%. Therefore, adding 0.6 g/L FeCl3 is the most beneficial in improving energy recovery and sulfate removal with low H2S content.