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

Abstract The stable H 2 production is the important link in the anaerobic biohythane fermentation. In order to address the key parameters for the stable H 2 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 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 H 2 content of 10.5%, where the H 2 yield efficiency was 248.0 mL-H 2 /COD removed . The success of operating R-TPAD was attributed to the proposed strategy, which used the tendency of existing CH 4 and the pH above 4.0 as the critical indicators for the stable H 2 production.