NOVELTY - Methanogenic anaerobic digestion method involves processing granular sludge in presence of nano-iron oxide for anaerobic digestion at 35 degrees C and pH 6.8-7.5 in anaerobic bed reactor. Culture medium is provided continuously to anaerobic reactor at 100L/day, where water flow is maintained at 10L/day, and hydraulic retention time is 6.5 days. Anaerobic reactor is equipped with outside circulation pump and provided with culture medium comprising sodium acetate (7000 mg/L), ammonium chloride (500 mg/L), potassium phosphite (1000 mg/L), and potassium hydrogen phosphite (2000 mg/L).    USE - Methanogenic anaerobic digestion method for improving activity of methanogenic anaerobic digestion and methane production (claimed).    ADVANTAGE - The methanogenic anaerobic digestion method ensures increased production efficiency.    DETAILED DESCRIPTION - Methanogenic anaerobic digestion method involves processing granular sludge in presence of nano-iron oxide for anaerobic digestion at 35 degrees C and pH 6.8-7.5 in anaerobic bed reactor. Culture medium is provided continuously to anaerobic reactor at 100L/day, where water flow is maintained at 10L/day, and hydraulic retention time is 6.5 days. Anaerobic reactor is equipped with outside circulation pump and provided with culture medium comprising sodium acetate (7000 mg/L), ammonium chloride (500 mg/L), potassium phosphite (1000 mg/L), potassium hydrogen phosphite (2000 mg/L) and nano ferroferric oxide (30%) in water solution. Obtained product is processed for ultrasonic dispersion at 30 degrees C for 2 hours in ultrasonic cleaner to obtain particles of nano ferroferric oxide having 0.1-10nm diameter for 30% particles. Ultrasonic cleaner is cleaned by using deionized water for 30 minutes to obtain clean static state anaerobic fermentation reactor. Culture medium is added to the reactor containing dispersed nano ferroferric oxide aqueous solution to obtain a mixture at a regulated pH of 6.9-7.1. Nitrogen is blew to the reactor at 34-36 degrees C with chemical oxygen demand value of 0.l-50 mg/L.