NOVELTY - Biogas cleaning system (111) comprises: (a) a gas control system for blending hydrogen gas into a biogas waste stream (1), having hydrogen flow controller and hydrogen port; (b) de-oxidizer catalyst bed fluidly coupled downstream of the gas control system; (c) an hydrodesulfurization catalyst bed fluidly coupled downstream of the de-oxidizer catalyst bed; (d) a first hydrogen sulfide removal adsorption bed fluidly coupled downstream of hydrodesulfurization catalyst bed; and (e) thermal sensor controller for measuring biogas stream temperature and in communication with gas control system.    USE - The system and the method are useful for purifying a biogas waste stream containing methane, carbon dioxide and water and impurities including sulfur, halides, siloxanes, and volatile organic compounds, to form a combustible clean biofuel (claimed). The clean biogas is useful as fuel in power generation systems of boilers, engines, turbines, or fuel cells.    ADVANTAGE - The biogas cleaning system provides the clean biogas with sufficiently low levels of contaminants (including sulfur of less than 50 ppb, halides of less than 50 ppb and siloxanes of less than 50 ppb) such that the biogas can be reliably and repeatably burned as fuel in a generator of internal combustion engine, turbine, fuel cell system and boiler, with reduced corrosion or damage to the generator.    DETAILED DESCRIPTION - Biogas cleaning system (111) comprises: (a) a gas control system for blending hydrogen gas into a biogas waste stream (1), having a hydrogen flow controller and hydrogen port; (b) a de-oxidizer catalyst bed fluidly coupled downstream of the gas control system for receiving and catalytically combusting the blended hydrogen with the remaining oxygen in the biogas such that oxygen is substantially removed from the biogas and the biogas stream is heated; (c) an hydrodesulfurization catalyst bed fluidly coupled downstream of the de-oxidizer catalyst bed that receives the heated biogas stream for the purpose of hydrogenating sulfur species to substantially hydrogen sulfide and hydrogenating chlorine species substantially to hydrogen chloride; (d) a first hydrogen sulfide removal adsorption bed fluidly coupled downstream of the hydrodesulfurization catalyst bed for the purpose of substantially removing sulfur from the biogas; and (e) a thermal sensor controller for measuring biogas stream temperature and in communication with the gas control system, thus when operable and receiving a biogas stream, hydrogen is mixed with the biogas, then the oxygen is substantially removed, the biogas stream is heated sufficiently by the exothermic combustion such that the sulfur species are hydrogenated by the hydrodesulfurization catalyst bed converted primarily to hydrogen sulfide, then the converted hydrogen sulfide is substantially removed the adsorbent bed, and further the rate of hydrogen blending is controlled in response to the thermal sensor controller. INDEPENDENT CLAIMS are also included for: a biogas cleaning method comprising: either (i) blending hydrogen with a biogas waste stream using a gas control system; (ii) combusting the blended hydrogen and biogas stream to remove oxygen and heat the biogas to 250-400 degrees C; (iii) then hydrogenating the resulting heated biogas stream, converting sulfides to substantially hydrogen sulfide; (iv) then absorbing hydrogen sulfide; and (v) controlling the hydrogen concentration in response to temperature; or (vi) pre-cooling a biogas waste stream reducing volatile organic compounds and water; (vii) adsorbing siloxanes substantially removing siloxanes from the biogas waste stream; (viii) adding hydrogen gas in the biogas stream; (ix) catalytically combusting the blended hydrogen with the remaining oxygen in the biogas such that oxygen is substantially removed from the biogas and the biogas stream is heated; (x) hydrogenating sulfur species to substantially hydrogen sulfide and simultaneously hydrogenating chlorine species to hydrogen chloride; (xi) adsorbing hydrogen chloride; (xii) adsorbing hydrogen sulfides using a sulfur adsorbent; (xiii) further adsorbing remaining hydrogen sulfides using a sulfur polisher; and (xiv) adjusting flow and temperature of the hot biogas returning to the economizer heat exchanger (110) to maintain the biogas temperature downstream of the de-oxidizer catalyst bed at 250 degrees C to no higher than 400 degrees C, thus a substantially clean biogas fuel is provided.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic flow diagram of the combination of elements of a biogas cleaning system.    Biogas waste stream (1)    Separator (100)    Heat exchanger (110)    Biogas cleaning system (111)    Refrigeration system (120)