The present invention provides a method and apparatus for the treatment of process gas from an anaerobic digestion system or a landfill gas system. In one embodiment, the system comprises a caustic scrubber including a vertical column having a top and a bottom and including a counter current flow system, wherein a process gas stream flows up vertically through the column in counter current flow to a caustic liquid solution that flows downward through the column. The caustic liquid solution removes at least one acid from the process gas stream, wherein treated gas that is substantially free of acids bubbles out through an opening at the top of the vertical column.