Patent ID: 8765451

Claim:
A method of treating an off-gas stream comprising NH 3 and H 2 S to provide a sulphate stream, the method comprising the steps of: providing a first off-gas stream comprising NH 3 , H 2 S, and CO 2 ; passing the first off-gas stream to an incinerator to oxidize NH 3 and H 2 S to provide a second off-gas stream comprising N 2 , H 2 O, SO 2 , and CO 2 ; scrubbing the second off-gas stream with a first aqueous alkaline stream in a caustic scrubber to separate SO 2 and a part of the CO 2 from the second off-gas stream to provide a spent caustic stream comprising carbonate and one or both of sulphite and bisulphate and a caustic scrubber off-gas stream comprising N 2 and CO 2 ; passing the spent caustic stream to an aerator comprising sulphur-oxidising bacteria in the presence of oxygen to biologically oxidize sulphite and bisulphite to sulphate to provide a sulphate stream.