in the gas chamber 19 at the top of the chamber and is extracted through gas conduit 32 u2033 the bubble generator 44 can have a diameter e g of 1 25 m and can have a plurality of orifices each having a diameter e g of 1 mm for generating bubbles of approximately the same diameter the bubble generator 44 can be in the form of for example a sieve plate wherein the carrier gas is pumped through the orifices in the sieve plate alternatively the bubble generator 44 can be in the form of a sparger with perforated pipes for distributing the carrier gas wherein the sparger distributes the bubbles through the perforated pipes which can extend from a central conduit the perforated pipes in the sparger can feature e g a radial multiple concentric ring spider web or hub and spoke wheel type configuration of the perforated pipes through which the carrier gas is pumped from an external source as shown in fig6 all components of the bubble column e g all walls and the bubble generator can be oriented at an angle to the vertical a between 0 u00b0 and 60 u00b0 with respect to vertical e g with respect to an axis along a radian passing through.