TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The siloxane adsorption bed is formed of activated carbon, silica get, molecular sieve, or zeolite. The de-oxidizer catalyst bed includes noble metal catalysts of platinum, palladium, rhodium, or metals in a reduced state. The hydrodesulfurization catalyst bed includes metals of cobalt, molybdenum or nickel. The hydrogen chloride removal adsorption bed comprises in part disodium oxide. The sulfur adsorption bed comprises active compound of zinc oxide, iron oxide, or activated carbon.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The gas control system provides added hydrogen concentration greater than 2%, and rate of combustion of the biogas stream at the de-oxidizer bed provides a biogas temperature of 250-400 degrees C, prior to the hydrodesulfurization catalyst bed. The biogas cleaning system further comprises: (f) a sulfur polisher adsorption bed fluidly coupled downstream of the first hydrogen sulfide removal adsorption bed in order to remove trace sulfur levels from the biogas, consisting in part of copper or nickel in a reduced or oxide state; a heat exchanger loop, (g) an economizer heat exchanger fluidly coupled upstream of de-oxidizer catalyst bed and to heated biogas stream exiting the hydrogen sulfide removal adsorption bed, where the cool heat exchange side includes the incoming biogas stream and outgoing cooled clean biogas, and the hot heat exchange loop is formed of outgoing clean heated biogas stream and the biogas stream upstream of de-oxidizer catalyst bed; (h) supplementary heater within the hot heat exchange loop for heating the biogas stream upstream of the de-oxidizer catalyst bed of 250-400 degrees C for substantial oxygen removal when there is insufficient exothermic temperature rise in the de-oxidizer catalyst bed; (i) supplementary cooler within the hot heat exchange loop for cooling the biogas steam, the cooler selected on of a second heat exchanger to reduce the temperature of the clean heated biogas stream and a biogas flow controller fluidly coupled to the sulfur adsorption bed, heat exchanger and outgoing cooled clean biogas stream and operable to distribute the hot clean biogas stream between the hot or cool exchange loops and heat exchanger in response to thermal sensor indicating there is excessive exothermic temperature rise within the de-oxidizer catalyst bed, thus in operation the flow and temperature of the hot biogas returning to the economizer heat exchanger, is adjustable to maintain the biogas temperature downstream of the de-oxidizer catalyst bed of 250 degrees C to no higher than 400 degrees C; (j) a chlorine removal adsorbent bed upstream of the first sulfur removal adsorbent bed; (k) a siloxane removal adsorption bed upstream of the heat exchanger for the purpose of removing siloxanes from the biogas; a biogas pre-cooler fluidly coupled upstream of hydrogen port from the group of refrigerant loop providing less than approximately -10 degrees F to condense water and contaminants, a refrigerant loop providing -10 degrees F to 32 degrees F to condense water and some contaminants, and a water condenser operable at 32-50 degrees F to condense out water content substantially; a biogas pre-cooler fluidly coupled upstream of hydrogen port, formed of a water sprayer and water separator (100) for the purpose of pre-cooling the biogas and to absorb some of the impurities such as sulfur dioxide and hydrogen sulfide in the water; many sulfur adsorbent beds with each is arranged in a lead and lag arrangement such that during operation one of the sulfur adsorbent bed is removed from biogas stream offline and changed while at least one other adsorbent bed is operable inline to the biogas stream; and an air inlet having a air flow controller fluidly coupled downstream of the siloxane removal adsorption bed, thus the air flow controller is in communication with and responsive to the thermal sensor controller such that additional air can be added to the biogas in a controlled manner in order to increase the exothermic heating of the biogas during combustion in the de-oxidizer catalyst bed. The biogas pre-cooler further comprises: a flow controller coupled to a first fluid conduit output of the pre-cooler heat exchanger and a bypass fluid conduit, to blend the biogas streams from the conduits to reduce the temperature of biogas leaving the pre-cooling system in response to a present target temperature; and an adsorption chiller coupled through a closed fluid loop thermally coupled to a second heat exchanger downstream of the sulfur polisher adsorption bed thus the heat required using the adsorption chiller is provided by the second heat exchanger for efficient energy use.