Abstract: Disclosed is an apparatus for scrubbing combustion gas, the gas being directed downwardly through a first scrubber passage having a first nozzle for feeding a scrubbing liquid that contacts the gas, a first filter material being held within the first scrubber passage and below the first nozzle, the gas being directed upwardly through a second scrubber passage optionally having a second nozzle for feeding additional scrubbing liquid that contacts the gas, and a cartridge for holding at least one second filter material within the second scrubber passage. The cartridge includes a first supply of limestone at least partially submerged in the scrubbing liquid, a supply of the borax above the first supply of the limestone, and a second supply of the limestone above the supply of borax.