Strategy of adjusting recirculation ratio for biohythane production via recirculated temperature-phased anaerobic digestion of food waste

The stable H₂ production is the important link in the anaerobic biohythane fermentation. In order to address the key parameters for the stable H₂ production in the recirculated temperature-phased anaerobic digestion (R-TPAD)system, a critical strategy was proposed to adjust the recirculation ratio (R). The adjusting strategy was examined on a lab-scale R-TPAD system. The R-TPAD system was started up and operated with R = 1. Another system without recirculation (R = 0)was also operated as the control system. By narrowing the probable range from 0 < R < 1, the value of R = 0.4 was obtained for stable biohythane production from R-TPAD system. The harvested R-TPAD process achieved the volatile solids removal of 84.8% and the biohythane yield of 475 L/kg-VS_fed with the H₂ content of 10.5%, where the H₂ yield efficiency was 248.0 mL-H₂/COD_removed. The success of operating R-TPAD was attributed to the proposed strategy, which used the tendency of existing CH₄ and the pH above 4.0 as the critical indicators for the stable H₂ production.