NOVELTY - The apparatus for the treatment of process gas (310), comprises a caustic scrubber (320) comprising a vertical column having a top and a bottom and including a counter current flow system. A process gas stream (330) flows up vertically through the column in counter current flow to a caustic liquid solution that flows downward through the column. The process gas is received from an anaerobic digestion system. The caustic liquid solution comprises a sodium hydroxide solution, removes an acid from the process gas stream, and is gravity trickled or sprayed within the vertical column.    USE - The apparatus is useful for the treatment of process gas (claimed) from an anaerobic digestion system or a landfill gas system, where the anaerobic digestion system is useful for the production of methane rich bio-gas that is useful as a cooking fuel.    ADVANTAGE - The apparatus enables efficient treatment of the process gas without the emission of green house gases into the atmosphere.    DETAILED DESCRIPTION - The apparatus for the treatment of process gas (310), comprises a caustic scrubber (320) comprising a vertical column having a top and a bottom and including a counter current flow system. A process gas stream (330) flows up vertically through the column in counter current flow to a caustic liquid solution that flows downward through the column. The process gas is received from an anaerobic digestion system. The caustic liquid solution comprises a sodium hydroxide solution, removes an acid from the process gas stream, and is gravity trickled or sprayed within the vertical column. The spent caustic liquid solution containing the acid flows through an opening in the bottom of the column and into a neutralization tank (360). The treated gas (330), which is free of acids, bubbles out through an opening at the top of the vertical column, and flows back into the anaerobic digestion system or a landfill gas system. The caustic scrubber is located within the anaerobic digestion system between an anaerobic digester and a biogas handling system or within the landfill gas system between landfill gas wells and landfill gas processing and treatment plant to protect the biogas handling system and other downstream equipment from corrosion or to protect the landfill gas processing and treatment plant and other downstream equipment from corrosion. The caustic scrubber allows total removal of hydrogen sulfide, hydrogen fluoride, hydrogen sulfate, hydrogen phosphate and hydrogen nitrate from the process gas stream so that acid concentration does not occur in downstream areas regardless of changing dew point and condensation. An INDEPENDENT CLAIM is included for a method for the treatment of process gas from an anaerobic digestion system using a caustic scrubber.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a caustic scrubber system.    Process gas (310)    Caustic scrubber (320)    Gas stream (330)    Treated gas (350)    Neutralization tank. (360)