NOVELTY - Method for removing contaminants in a biogas, involves heating and aerating anaerobic digester effluent in aeration reactor to produce alkaline effluent, contacting the alkaline effluent with input biogas in reactor to produce treated biogas and resulting effluent with lower pH as compared to the pH of the alkaline effluent, and recovering the treated biogas, where the treated biogas has less hydrogen sulfide as compared to the input biogas.    USE - The method and system are useful for removing contaminants in biogas (claimed).    ADVANTAGE - The method is simple and cost-effective, and increases lifespan of engine in the system. The system is simple to construct and to maintain, and has excellent heat and mass transfer, and ability to handle solid particles without clogging.    DETAILED DESCRIPTION - Method for removing contaminants in a biogas, involves (a) (i) heating and aerating anaerobic digester effluent in aeration reactor to produce alkaline effluent, (ii) contacting the alkaline effluent from step (i) with input biogas in reactor to produce treated biogas and resulting effluent with lower pH as compared to the pH of the alkaline effluent, and (iii) recovering the treated biogas from step (b), where the treated biogas has less hydrogen sulfide as compared to the input biogas, or (b) (i) heating and aerating an anaerobic digester effluent in an aeration reactor to produce an alkaline effluent, (ii) contacting the alkaline effluent from step (i) with an input biogas in reactor to produce treated biogas and resulting effluent with lower pH as compared to the pH of the alkaline effluent, (iii) recovering the treated biogas from step (i), where the treated biogas has less hydrogen sulfide as compared to the input biogas, (iv) aerating the resulting effluent of step (ii) to produce a regenerated effluent with an alkaline pH, and (v) contacting the regenerated alkaline effluent of step (iv) with the recovered biogas of step (iii) to remove carbon dioxide in the biogas. An INDEPENDENT CLAIM is included for system for collecting the above-mentioned biogas.