Method of potting hollow fiber membranes

#This application is a continuation of Ser. No. 09/849,573 filed May 4, 2001; which is a continuation of Ser. No. 09/507,438 filed Feb. 19, 2000 issued as U.S. Pat. No. 6,294,039; which is a division of Ser. No. 09/258,999, filed Feb. 26, 1999, issued as U.S. Pat. No. 6,042,677; which is a division of Ser. No. 08/896,517, filed Jun. 16, 1997, issued as U.S. Pat. No. 5,910,250; which is a continuation-in-part application of Ser. No. 08/690,045, filed Jul. 31, 1996, issued as U.S. Pat. No. 5,783,083 which is a non-provisional of provisional application Serial No. 60/012,921 filed Mar. 5, 1996 and a continuation-in-part of Ser. No. 08/514,119, filed Aug. 11, 1995, issued as U.S. Pat. No. 5,639,373. The disclosure of all the patents and applications listed above are hereby incorporated by reference thereto as if fully set forth herein.

#This invention relates to a membrane device which is an improvement on a frameless array of hollow fiber membranes and a method of maintaining clean fiber surfaces while filtering a substrate to withdraw a permeate, which is also the subject of U.S. Pat. No. 5,248,424; and, to a method of forming a header for a skein of fibers. The term “vertical skein” in the title (hereafter “skein” for brevity), specifically refers to an integrated combination of structural elements including (i) a multiplicity of vertical fibers of substantially equal length; (ii) a pair of headers in each of which are potted the opposed terminal portions of the fibers so as to leave their ends open; and, (iii) permeate collection means held peripherally in fluid tight engagement with each header so as to collect permeate from the ends of the fibers.

#The term “fibers” is used for brevity, to refer to “hollow fiber membranes” of porous or semipermeable material in the form of a capillary tube or hollow fiber. The term “substrate” refers to a multicomponent liquid feed. A “multicomponent liquid feed” in this art refers, for example, to fruit juices to be clarified or concentrated; wastewater or water containing particulate matter; proteinaceous liquid dairy products such as cheese whey, and the like. The term “particulate matter” is used to refer to micron-sized (from 1 to about 44 μm) and submicron sized (from about 0.1 μm to 1 μm) filterable matter which includes not only particulate inorganic matter, but also dead and live biologically active microorganisms, colloidal dispersions, solutions of large organic molecules such as fulvic acid and humic acid, and oil emulsions.

#The foregoing and additional objects and advantages of the invention will best be understood by reference to the following detailed description, accompanied by schematic illustrations of preferred embodiments of the invention, in which illustrations like reference numerals refer to like elements, and in which:

#FIG. 1 is a graph in which the variation of flux is plotted as a function of time, showing three curves for three runs made with three different arrays, in each case, using the same amount of air, the identical membranes and the same membrane surface area. The results obtained by Yamamoto et al are plotted as curve 2 (under conditions modified to give them the benefit of doubt as to the experimental procedure employed, as explained below); the flux obtained using the gas-scrubbed assembly of the '424 patent is shown as curve 1; and the flux obtained using the gas-scrubbed assembly of this invention is shown as curve 3.

#FIG. 2 is a perspective exploded view schematically illustrating a membrane device comprising a skein of fibers, unsupported during operation of the device, with the ends of the fibers potted in a lower header, along with a permeate collection pan, and a permeate withdrawal conduit. By “unsupported” is meant ‘not supported except for spacer means to space the headers’.

#The skein of this invention may be used in a liquid-liquid separation process of choice, and more generally, in various separation processes. The skein is specifically adapted for use in microfiltration processes used to remove large organic molecules, emulsified organic liquids and colloidal or suspended solids, usually from water. Typical applications are (i) in a membrane bioreactor, to produce permeate as purified water and recycle biomass; for (ii) tertiary filtration of wastewater to remove suspended solids and pathogenic bacteria; (iii) clarification of aqueous streams including filtration of surface water to produce drinking water (removal of colloids, long chain carboxyic acids and pathogens); (iv) separation of a permeable liquid component in biotechnology broths; (v) de-watering of metal hydroxide sludges; and, (vi) filtration of oily wastewater, inter alia.

#The problem with using a conventional membrane module to selectively separate one fluid from another, particularly using the module in combination with a bioreactor, and the attendant costs of operating such a system, have been avoided. In those instances where an under-developed country or distressed community lacks the resources to provide membrane modules, the most preferred embodiment of this invention is adapted for use without any pumps. In those instances where a pump is conveniently used, a vacuum pump is unnecessary, adequate driving force being provided by a simple centrifugal pump incapable of inducing a vacuum of 75 cm Hg on the suction side.

#The fibers used to form the skein may be formed of any conventional membrane material provided the fibers are flexible and have an average pore cross sectional diameter for microfilitration, namely in the range from about 1000 Å to 10000 Å. Preferred fibers operate with a transmembrane pressure differential in the range from 7 kPa (1 psi)-69 kPa (10 psi) and are used under ambient pressure with the permeate withdrawn under gravity. The fibers are chosen with a view to perform their desired function, and the dimensions of the skein are determined by the geometry of the headers and length of the fibers. It is unnecessary to confine a skein in a modular shell, and a skein is not.