CO2 is dissolved into water at high pressure. Biogas
is passed through a counter flow of this water in a
packed column to enhance contact between the
gas and the water. CO2 is dissolved in the water at
a higher rate than CH4 so the biogas escaping at
the top of the vessel will have a lower relative
concentration of CO2. The scrubbing water,
containing mainly dissolved CO2 but also some CH4,
is then brought to a flash tank where pressure is
reduced. The CH4 departs first and is re‐circulated
to the water scrubbing column. Thus, the relative
CH4 concentration in the biogas gradually
increases. The CO2 that is desorbed in the flash
tank is ejected to the atmosphere through a filter
that absorbs potential remnants of H2S.
Water scrubbing will result in approximately 2
litres of discharged scrubbing water per normalcubic meter (nm3) of raw biogas that is processed