TECHNOLOGY FOCUS - TEXTILES AND PAPER - Preferred Components: (F1) Have an outside diameter of at most100 microns; a hollow area of at least10 (preferably at least30)% and at most50%. (F1) Are non-porous or dense-walled; and comprise polymethyl pentene. (F1) Have second end; have length of 0.25 - 3.0 (preferably 1 - 2) meters; are arranged into groups comprising 24 - 96 hollow fibers. The groups further comprise second fibers that are stronger than (F1). The group is a tow of fibers, thread, yarn or twisted fibers, that are curled, crimped or undulating along their length. The outer surface of the fibers is non-wetting to water; the fiber is asymmetric; the outer surface of (F1) is less porous than inner layer of the fibers; the thermal mechanical treatment includes stretching and weak cooling; (F1) have a layer with pores of at most30 Angstrom and pores of greater than 30 (preferably 20 - 40) Angstrom . The increased permeability to oxygen is at least 3 times the permeability of un-modified fiber material.    TECHNOLOGY FOCUS - POLYMERS - The thermoplastic polymer is a polyolefin (preferably polymethyl pentene, polypropylene or polyethylene).    TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Apparatus: (F1) Extend along their length in a first direction. The apparatus further comprises third fibers extending along their length in second direction, the second perpendicular to the first direction. The third fibers and hollow fibers are intertwined to form a fabric. The fabric is continuous across the length of (F1), and extends over a portion of the length of the hollow fibers near their open ends and does not extend over a central portion of the length of the fibers. (F1) And third fibers are woven, knitted, stitched or warp knitted together over at least a portion of the length of (F1). (F1) Have second open ends, which are potted in a second header; communicate with a second port of the second header through a second cavity of second header; the header and second header are spaced apart from each other and (F1) are arranged into at least one flat sheet or parallel planar structure extending between the headers; the flat sheets or planar structures are parallel to each other; adjacent planar structures have spacing between them of 2 - 20 (preferably 3 - 15) mm; and the first header and second header are held apart at a distance that applies a tensile force to (F1). The apparatus further comprises spacers between the flat sheets or planar elements outside the header. The flat sheets or planar structures further comprise a rigid member extending between the headers. The ratio of surface area for oxygen transfer to surface area of supported biofilm is at least 1.6, (preferably at least 2, especially at least 5) or at most1. The roughness of the fabric is 0.1 - 2 mm. (F1) Have a reduced O2/N2 selectivity of at most1.5 or at most3 (preferably greater than 1). Preferred Reactor: The reactor further comprises an agitator or aerator adapted to agitate the liquid around the apparatus; a chemical injection system for injecting chemicals into either the lumens of (F1) or a part of the reactor in communication with the outer surfaces of (F1); and a heater to heat either the gas provided to the port or the liquid held in the tank. A multi-stage reactor has at least two reactors with the outlet of the first reactor connected to the inlet of a second reactor; the first and second reactors are plug flow reactors, batch reactors or continuously stirred reactors. The apparatus of the second reactor has a lower ratio of surface area for oxygen transfer to surface area of supported biofilm than the apparatus of the first reactor (preferably at least 5 for the apparatus of the first reactor and at most5 for the apparatus of the second reactor). The reactor or multi-stage reactor has several apparatus arranged in parallel between the inlet and outlet. In the multi-stage reactor the fibers of the apparatus of first reactor are formed into a sheet along their entire length while the fibers of the apparatus of second reactor are unsupported by perpendicular fibers over a portion of their length.Preferred Process: The liquid is wastewater; the gas comprises oxygen or hydrogen; (B1) is maintained in an aerobic state adjacent the outer surfaces and in an anoxic or anaerobic state adjacent the liquid. The liquid is contacted with the apparatus in a batch or continuous process; the liquid is stirred continuously or intermittently; the liquid moves past the outer surfaces in a plug flow; (B1) is maintained in a state of endogenous growth (preferably by providing a food to microorganisms (F/M) ratio of at most0.09 kgCODt (total COD)/kgMLSS (mixed liquor suspended solids)/day, and by limiting the supply of oxygen to (B1) performed upstream of or prior in time to the process). The process further involves providing feed water at F/M ratio of at least 0.09 kgCODt/kgMLSS/day. The process is performed in a septic tank, shipboard system, or to treat wastewater taken directly from houses, businesses or parts of ship. (B1) Is maintained at thickness of 0.05 - 2 (preferably 0.1 - 1) mm. The process further involves maintaining at least a portion of (B1) so that its thickness alternately increases and decreases, increasing in thickness over first periods of time, and reducing thickness between the first periods of time. The thickness of only a portion of (B1) is reduced at a time, the reducing is by air scouring or agitating at least portion of liquid; by contacting at least a portion of (B1) with a second liquid containing worms or other animals which digest (B1); by applying ozone to at least a portion of (B1) from the lemen side of the fibers or from the outside of (B1) to oxidize the portion of (B1) and then maintaining (B1) to digest the oxidized portion; by introducing ozone gas into the port followed by supplying oxygen to the port; by supplying air to the port while the liquid is removed from contact with (B1) or provided at a loading of less than 0.1 kg CODs per kg MLSS per day to digest (B1) aerobically; or by applying a control agent to at least portion of the outer surface of (B1). The control agent is clean water; heated (preferably at 40 - 60degreesC) clean water; ozone gas; an alkali solution with a pH 8 - 13 (preferably 9 - 11) or 1 - 6 (preferably 3 - 4); a second liquid which is agitated or aerated while in contact with (B1) by digesting (B1) aerobically after the control agent is applied; by draining the liquid away from contact with (B1); by stopping or reducing the supply of oxygen to the port from time to time or periodically to create alternating aerobic and anoxic or anaerobic conditions in a portion of (B1); or by physically removing a portion of (B1) by spraying it with a third liquid or scraping it with a brush or scraper. The liquid is removed from a portion of (B1) while reducing its thickness. The amount of oxygen supplied to the port is increased when the COD (chemical oxygen demand) of the liquid is increased. The liquid is periodically removed from (B1) and replaced with a fresh batch of liquid and the supply of the gas is continued while the liquid is being removed, while the biofilm is not in contact with the liquid or while a fresh batch of liquid is being replaced in contact with (B1). After treatment the liquid has suspended solids less than 10 mg/l, and CODs less than 50 mg/l. The process is operated in two stages, the first stage reduces the COD of the liquid to less than 300 (preferably 200 - 300) mg/l. Before treatment the liquid has CODs of at least1000 mg/l and the apparatus has ratio of surface area for gas transfer to area of attached (B1) of at least1 (preferably 1 - 10); or CODs at most1000 mg/l and apparatus having ratio of surface area for gas transfer to area of attached (B1) of 0.2 - 2.5; or CODs approximately 300 mg/l and apparatus having ratio of surface area for gas transfer to area of attached (B1) of 0.1 - 1. The thickness of (B1) is reduced at least every 10 days or after the biofilm has digested between 20 - 200 g CODs/m2 of biofilm area since the last reduction. The process is operated as a batch process involving draining the liquid from a tank containing the apparatus; the draining step further involves draining a first part of the liquid containing settled solids to a first treatment system and draining a second part of the liquid to a second treatment system. The process further involves growing a biofilm on the outer surfaces of the medium, the oxygen travelling through the biofilm and into the substrate; and maintaining (F1) under endogenous respiration. The apparatus has an exhaust port, the gas is air, and the gases flow through the apparatus from the port to the exhaust port; the exhaust gas has higher concentration or mass flow rate of carbon dioxide than inlet gas; and performing nitrification in the biofilm and removal of COD. At least 100 mg/hour of oxygen per liter of substrate is transferred. (B1) Has thickness of at least 20 microns. The process further involves maintaining the substrate at a low soluble COD concentration and air scrubbing the biofilm to maintain it under a certain thickness; providing air bubbling for adding additional oxygen to the substrate, mixing the substrate and/or maintaining bacteria in suspension in the substrate. EXAMPLE - A bench scale bioreactor was made using a module having a single sheet of fibers. The length of the sheet was 0.57 m and height 0.45 m, providing a total biofilm area of approximately 0.5 m2 assuming that both sides of sheet available for biofilm growth. The ratio of surface area for gas transfer surface area of attached biofilm was about 5 - 6. Inlet air flow was 25 ml/minute at a pressure 34.5 kPa. Reactor volume was 30 l. A synthetic wastewater with a COD (chemical oxygen demand) level of 1000 mg/l was introduced in a batch manner periodically. The wastewater consisted of soluble peptone (1 mg/l) (to accelerate the initial growth of biofilm on the sheet) and sodium hydrogen phosphate (0.03 g/l) dissolved in tap water. Batch reactions were conducted. The results of three batch periods were as follows: a three day period from day 2 to day 5, a three day period from day 6 to day 9, and a one day period from day 9 to day 10. It was observed that 80 - 90% reduction in COD was achieved in each of the three-day batch periods, and 40% COD reduction was achieved in a one-day batch period. The oxygen transfer efficiency during the test was 50 - 70%, as measured by the exit concentration of air.