Bioreactor

1. A bioreactor for microbial conversion of at least one conversion substrate, which comprises a treatment zone to accommodate when in use a solution of said at least one conversion substrate, a culture holding zone to accommodate when in use a microbial culture capable of metabolising said at least one conversion substrate, a source of primary growth substrate for the microbial culture, a first permeable membrane forming an interface between the treatment zone and the culture holding zone, and a second permeable membrane forming an interface between the source of primary growth substrate and the culture holding zone, the first permeable membrane being of a material which will allow passage of the at least one conversion substrate from the treatment zone to the culture holding zone whilst being impermeable to the microbial culture, the second permeable membrane being of a material permeable to the primary growth substrate but substantially impermeable to water.

2. A bioreactor according to claim 1 wherein the culture holding zone is defined by boundaries of a chamber, the treatment zone is external of the chamber and the second permeable membrane forms at least a part of a hollow member situated within the chamber.

3. The bioreactor of claim 1 , wherein the conversion substrate is at least one alkoxy compound selected from branched alkyl ethers and branched alkyl alcohols and the primary growth substrate is at least one hydrocarbon of up to 12 carbon atoms.

4. The bioreactor of claim 1 , wherein the conversion substrate comprises methyl tert-butyl ether and the primary growth substrate is at least one alkane of up to 6 carbon atoms.

5. The bioreactor of claim 1 , wherein the first permeable membrane is substantially impermeable to water.

6. A process of operating a bioreactor suitable for conversion of at least one conversion substrate, which bioreactor comprises a treatment zone to accommodate when in use a solution of said at least one conversion substrate, a culture holding zone to accommodate when in use a microbial culture capable of metabolizing said at least one conversion substrate, a source of primary growth substrate for the microbial culture, a first permeable membrane forming an interface between the treatment zone and the culture holding zone, and a second permeable membrane forming an interface between the source of primary growth substrate and the culture holding zone, the first permeable membrane being of a material which will allow passage of the at least one conversion substrate from the treatment zone to the culture holding zone whilst being impermeable to the microbial culture, the second permeable membrane being of a material permeable to the primary growth substrate but substantially impermeable to water, wherein said process comprises introducing a solution of said at least one conversion substrate into the treatment zone, supplying primary growth substrate from said source through the second permeable membrane at a rate sufficient to promote conversion of said at least one conversion substrate by the microbial culture, and removing treated solution from the treatment zone.

7. A process of claim 6 , wherein the solution of said at least one conversion substrate is water contaminated with at least one alkoxy compound selected from branched alkyl ethers and branched alkyl alcohols, wherein the primary growth substrate is at least one hydrocarbon of up to 12 carbon atoms.

8. A process of claim 7 , wherein the at least one alkoxy compound comprises methyl tert-butyl ether and the hydrocarbon growth substrate is at least one alkane of up to 6 carbon atoms.

9. A process of claim 7 , wherein for the in-situ treatment of water contaminated with at least one alkoxy compound selected from branched alkyl ethers and branched alkyl alcohols wherein the bioreactor is located in an aquifer containing the water contaminated with the at least one alkoxy compound.