In one embodiment, a method includes gasifying a fuel source using a first oxygen stream supplied from an air separation unit (ASU), discharging a gasifier blowdown from a gasification and scrubbing system configured to gasify the fuel source, generating a grey water from the gasifier blowdown, and biologically treating the grey water in a reactor using a second oxygen stream supplied by the ASU.

A process for synthesising hydrocarbons is described comprising the steps of (a) making a synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide from a feedstock in a synthesis gas generation unit, (b) removing carbon dioxide to produce a carbon dioxide stream and purified synthesis gas comprising hydrogen and carbon monoxide for synthesis in a Fischer-Tropsch hydrocarbon synthesis unit wherein (i) at least a portion of the FT water stream is fed to an electrolysis unit to provide an oxygen stream, which is fed to the synthesis gas generation unit. Carbon dioxide stream recovered from the carbon dioxide removal unit and a portion of the hydrogen stream produced by the electrolysis unit are fed to a reverse water-gas shift unit to produce a carbon monoxide stream, with carbon monoxide stream from the reverse water-gas shift unit is fed to the Fischer-Tropsch hydrocarbon synthesis unit.