Syngas are produced from wastewater through anaerobic reactions and thermochemical processes, using a catalyst that modifies the gas composition, reduces methane production, and achieves partial COD reduction. The current research is attempting to treat the tannery wastewater via an anaerobic process configured with 0.25, 0.3, and 0.35 volume units of granular activated carbon (GAC) with 10 nm size to minimize the concentration of chemical oxygen demand (COD) and improve the biological methane yield. During this anaerobic process, the up-flow anaerobic sludge blanket (UASB) reactor supports to enhance the bio-methane production and handle the high rate of organic load. Influences of GAC units and operating time (days) on COD and biological methane yield of an anaerobic system for tannery wastewater treatment are studied and measured in their value. The output results of COD and biological methane yield are compared, and it was spotted that the tannery water process with 0.3 volume units of GAC owns 87% of COD removal with biological methane yield of 66.3 mL/day (7.2 mL/g COD removed) and end of 30th day found 1939 mL.