NOVELTY - Method for enhancing biomethanation by thermophilic aerobic digestion of combined vegetable and agro waste, involves (a) preparing homogenized slurry of vegetable waste, (b) feeding the first digester with predefined quantity of vegetable waste slurry at predefined intervals, withdrawing digested slurry from the first digester, feeding the predefined quantity of digested slurry of the first digester to the mesophilic digester and aerating the first digester, and (c) reinjecting outgoing slurry back in the zero dissolved oxygen zone of the second mesophilic digester.    USE - The method is useful for enhancing biomethanation by thermophilic aerobic digestion of combined vegetable and agro waste, preferably food waste, cow dung and agro waste.    ADVANTAGE - The method is cost-effective and environmentally-friendly, and rapidly improves growth and population of bacteria.    DETAILED DESCRIPTION - Method for enhancing biomethanation by thermophilic aerobic digestion of combined vegetable and agro waste, involves (a) preparing homogenized slurry of vegetable waste and filling first digester and second digester with seed slurry for energizing digesters for predefined period, where the first digester is thermophilic digester and the second digester is mesophilic digester, (b) feeding the first digester with predefined quantity of vegetable waste slurry at predefined intervals, withdrawing predefined quantity of digested slurry from the first digester, feeding the predefined quantity of digested slurry of the first digester to the mesophilic digester and aerating the first digester intermittently to maintain thermophilic aerobic condition within the first digester, where concentration of volatile fatty acid produced in the first digester varies with the aeration to cause enhanced biogas production, and (c) reinjecting the 1-10% outgoing slurry back in the zero dissolved oxygen (DO) zone of the second mesophilic digester for enhancing rate of growth of methanogens and faster utilization of nutrients and volatile fatty acids (VFA) to produce biogas containing methane. An INDEPENDENT CLAIM is included for system for enhancing biomethanation by thermophilic aerobic digestion of combined vegetable and agro waste, which comprises first thermophilic digester maintained at 55 degrees C for receiving biodegradable material, preferably cow dung/vegetable waste/agro waste/kitchen waste in form of water material, second mesophilic digesters capable for receiving predigested material received from the first thermophilic digester, and aerator for supplying oxygen to the first thermophilic digester for generating optimum number of bacteria and maximum amount of volatile fatty acids (VFA) by aerobic bacteria under thermophilic condition, where the reinjection involves passing at least 1-10% outgoing slurry from the second mesophilic digester back to second mesophilic digester which enhances rate of growth of methanogens in second digester that result in faster utilization of the VFAs and optimum production of methane.