Three identical cylindrical digesters were made of polyethylene with total capacity of each at 160 L. The
temperature of the fermentation rely on the ambient temperature and the mixing process is passive stirring, which
occurred by the insertion of new feeding and the subsequent thermal convection streams as well as by the up-flow of
gas bubbles1. Each digester was connected to a water displacement unit, manometer, and thermometer. The
schematic arrangement for a unit of digester is provided from Figure 1.
The three digesters were utilized and differed based on the OLR factors. The feeding strategy was conducted in a
continuous manner by flowing in 3 L CH co-substrate, making the hydraulic retention time (HRT) set at 30 d. The
feeding process was repeated for every 24 h.