Supported biofilm apparatus
A membrane supported biofilm reactor uses modules having fine, hollow fibers, for example, made from melt spun thermoplastic polymers treated after spinning to increase their permeability to oxygen, used, for example, in tows or formed into a fabric. In one module, one or more sheets of the fabric are potted into a module to enable oxygen containing gas to be supplied to the lumens of the hollow fibers. Various reactors and processes, for example to treat wastewater, using such modules are described. In one process, oxygen travels through fibers, optionally through an attached biofilm, to oxygenate surrounding water. Mechanical, chemical and biological methods, for example endogenous respiration, are used to control the thickness of the biofilm.
1. An apparatus for supporting a biofilm in a liquid comprising:
a) a plurality of gas permeable hollow fibers, each hollow fiber having a lumen, an outer surface and an open end; and,
b) a header, the header having a cavity and a port open to the cavity,
wherein the hollow fibers extend from the header, with the outer surfaces of the open ends of the hollow fibers sealed to the header and the lumens of the hollow fibers communicating with the port through the cavity
and wherein the fibers are made of a melt spun thermoplastic polymer subjected to thermal or mechanical treatment after spinning to have at least an annular region of increased permeability to oxygen without permitting a flow of liquid water through the walls of the fibers from the outer surfaces of the fibers to the lumens, and wherein the increased permeability to oxygen is at least 3 times the permeability of un-modified fiber material.
2. The apparatus of claim 1 wherein the hollow fibers have a second end and are between 0.25 metres and 3.0 metres long.
3. The apparatus of claim 1 wherein the hollow fibers are arranged into groups.
4. The apparatus of claim 3 wherein the groups further comprise second fibers that are stronger than the hollow fibers.
5. The apparatus of claim 1 wherein the hollow fibers extend along their length generally in a first direction and further comprising third fibers extending along their length generally in a second direction, the second perpendicular to the first direction.
6. The apparatus of claim 1 wherein the hollow fibers have second open ends and the second open ends of the hollow fibers are potted in a second header and communicate with a second port of the second header through a second cavity of the second header.
7. The apparatus of claim 6 wherein the header and the second header are spaced apart from each other and the hollow fibers are arranged into one or more flat sheets or generally parallel planar structures extending between the headers.
8. The apparatus of claim 1 having a surface area for oxygen transfer to surface area of supported biofilm ratio of about 1.6 or more.
9. The apparatus of claim 1 wherein the thermoplastic polymer is one of PMP, PP or PE.
10. The apparatus of claim 1 wherein the hollow fibers have a reduced selectivity.
11. The apparatus of claim 1 wherein the O 2 /N 2 selectivity of the fibers is 3 or less.
12. The apparatus of claim 1 wherein the outer surface of the fibers is non-wetting to water.
13. The apparatus of claim 1 wherein the fiber is asymmetric.
14. The apparatus of claim 1 wherein the outer surface of the fibers is less porous than an inner layer of the fibers.
15. The apparatus of claim 1 wherein the thermal mechanical treatment includes steps of stretching and weak cooling.
16. The apparatus of claim 1 wherein the fibers have a layer with pores of 30 Angstroms or less.
17. The apparatus of claim 1 wherein the fibers have a layer with pores of greater than 30 Angstroms.
18. The apparatus of claim 1 having a layer with a pore size between 20 and 40 Angstroms.