NOVELTY - Obtaining biogas involves using cotton stalk (45-55 pts. wt.), food waste (32-48 pts. wt.), manure (14-22 pts. wt.), calcium hydroxide (2-3 pts. wt.), biogas slag (5-9 pts. wt.) and inoculum (8-13 pts. wt.). Water is added to calcium hydroxide solution to obtain aqueous solution of lime with calcium hydroxide content of 1-3 wt.%. The cotton stalk is pulverized to a size of 4cm or less and the food waste is pulverized to a size of 3cm or less.    USE - Method for obtaining biogas (claimed).    ADVANTAGE - The method enables to obtain eco-friendly biogas with high combustion rate and reduces the introduction of exogenous chemical additives.    DETAILED DESCRIPTION - Obtaining biogas involves using cotton stalk (45-55 pts. wt.), food waste (32-48 pts. wt.), manure (14-22 pts. wt.), calcium hydroxide (2-3 pts. wt.), biogas slag (5-9 pts. wt.) and inoculum (8-13 pts. wt.). Water is added to calcium hydroxide solution to obtain aqueous solution of lime with calcium hydroxide content of 1-3 wt.%. The cotton stalk is pulverized to a size of 4cm or less and the food waste is pulverized to a size of 3cm or less. The pulverized cotton stalk is soaked in the aqueous solution of lime in the mass ratio of 0.35-0.5 at 26-28 degrees C for 3- 5 days and the moisture content of cotton stalks is controlled at 55-60%. The animal manure is placed at 35-38 degrees C for 5-7 days to obtain acidified feed solution. Water is added to the acidified feed solution to adjust the concentration to 20-25%. The pulverized food waste, pretreated cotton stalks, biogas and inoculum are mixed and fermented at 34-36 degrees C for 30-35 days to obtain broth. The obtained biogas is desulfurized by the dehydration process and gas turbine are driven for power generation. The residue is removed after fermentation by solid-liquid separation to obtain a solid residue and slurry. The solid residue (8-10 wt.%) is used as inoculum for the next batch and rest of the solid residue is used as solid organic fertilizer for farmlands or greenhouses where the water content in the fermented biogas is 60-80 wt.%.