NOVELTY - System (300) to purify biogas, comprises: a gas compressor (328) to increase the pressure of the biogas for processing; a gas processor (332) to remove any carbon dioxide, volatile organic compounds and hydrogen sulfide, from the gas; a biological sulfur removal system (334) to treat off-gas from the processor; a regenerative thermal oxidizer system to treat gas; a catalytic oxygen removal system (354) to receive product gas from the processor and remove oxygen from the product gas; and a caustic scrubber to receive product gas and neutralize any acid formed during catalytic oxygen removal.    USE - The system is useful for the purification of biogas.    ADVANTAGE - The system: provides purified biogas with reduced odors and methane emissions, and thus creates two renewable resources; utilizes biological sulfur removal systems which are several orders in magnitude lower in cost than expensive sulfur removal systems e.g. media or iron chelating systems; and is economical and exhibits increased plant efficiency by eliminating the penalty associated with conventional thermal oxidizers.    DETAILED DESCRIPTION - System (300) for purifying biogas, comprises: a gas compressor (328) to increase the pressure of the biogas for processing; a gas processor (332) to remove any carbon dioxide, volatile organic compounds and hydrogen sulfide, from the gas; a biological sulfur removal system (334) to treat off-gas from the gas processor; a regenerative thermal oxidizer system to treat gas from the biological sulfur removal system for thermal destruction of volatile organic compounds, hydrogen sulfide, and methane slipped from the gas processor; a catalytic oxygen removal system (354) to receive product gas from the gas processor and remove oxygen from the product gas; and a caustic scrubber to receive product gas from the catalytic oxygen removal system and neutralize any acid formed during catalytic oxygen removal. An INDEPENDENT CLAIM is also included for purification of biogas, comprising: increasing the pressure of the biogas using a gas compressor; removing any carbon dioxide, volatile organic compounds and hydrogen sulfide, from the gas using a gas processor; treating off-gas from the gas processor using a biological sulfur removal system; treating gas from the biological sulfur removal system using a regenerative thermal oxidizer system for thermal destruction of volatile organic compounds, hydrogen sulfide and methane slipped from the gas processor; receiving product gas from the gas processor and removing oxygen from the product gas using a catalytic oxygen removal system; and receiving product gas from the catalytic oxygen removal system and neutralizing any acid formed during catalytic oxygen removal using a caustic scrubber.    DESCRIPTION OF DRAWING(S) - The figure shows a flow diagram illustrating the system and method for the purification of biogas.    System (300)    Gas compressor (328)    Gas processor (332)    Biological sulfur removal system (334)    Catalytic oxygen removal system (354)