Systems and methods for liquefying a gaseous fluid that comprises at least 50% by volume methane into a liquefied fluid that comprises at least 85% by volume methane. Processing can include increasing a pressure of the incoming gaseous fluid to between 10 and 50 bar; pre-treating the gaseous fluid using membrane filtering to a retentate stream having a methane content of at least 85% by volume; liquefying the retentate stream by cryogenic cooling to a temperature between −100° C. and −140° C.; flashing the liquefied fluid into a container; retrieving processed liquid fluid at a first container level at a pressure of between 1 and 10 bar, a temperature of between −120° C. and −160° C., and a methane concentration of at least 85% by volume into a storage device; and retrieving a slurry flow comprising solid CO2 and water ice at a second container level below the first container level.