Using combustion ash produced by refuse incineration plants to absorb the CO2 in biogas is nothing new, and for this reason is often discussed in the context of technologies used to upgrade biogas. Recently, however, groups of Swedish researchers have experimented with using ash derived from forest biomass rather than from refuse. Laboratory and full-scale tests have both shown a greater efficiency in the upgrading process as well as the possibility to exploit waste materials that would otherwise not be utilized.