Abstract: Limitation of the number of cassettes in an assembly currently used for the production of permeate is obviated by grouping plural cassettes into racks one or more of which may be isolated while permeate production from the remaining racks is uninterrupted. Ancillary functions such as back-pulsing, chemical cleaning and testing for defects in membranes (“integrity testing”) in one or more racks may proceed while production of permeate continues. The number of racks in a bank is determined by the period of the overall filtration cycle, typically 15 min, in which filtration period the ancillary period is a minor portion, typically 30 sec. The racks make it possible to use automatic on/off valves which open and close quicker than larger ones. The resulting saving in time, energy, and equipment costs, which when back-pulsing with permeate is surprisingly economical, is even greater when a chemical cleaning solution is to be used.

Abstract: The outer surfaces of hollow fiber membranes in a skein, or a bank or cassette of stacked skeins, are kept essentially free of solids by maintaining a substantially uniform flow of a stream of coarse bubbles through each of plural orifices in an aerator disposed beneath the fibers. Aerators for skeins used in microfiltration of wastewater in a tank are periodically flushed when their air orifices are fouled, by injecting a flushing fluid into a fouled aerator. The flushing fluid may be a two-phase mixture of flushing liquid and air, or flushing liquid only. The flushing liquid may be permeate, clean water or wastewater (substrate). When air is injected into the flushing liquid flowed to an aerator for less than 5 min, preferably less than 20 sec, the flushing fluid produces discrete masses of liquid which are flowed laterally through the body of the aerator, cleaning its walls and maintaining the orifices essentially free from plugging.

Abstract: An adaptive control method for producing high purity water, the method having the ability to produce high purity water on a continuous basis having a resistivity in the range of 0.8 to 4 megohm-cm. The method comprises the steps of providing a feedwater to be purified and providing a first reverse osmosis unit having a first high pressure side and a first low pressure side and having a first permeate produced at the first low pressure side. The pH of the feedwater to be introduced to the high pressure of the first reverse osmosis unit is monitored before introducing the feedwater to the high pressure side of the first reverse osmosis unit. Also, the feedwater is maintained in a temperature range of 45.degree. to 80.degree. F. A second reverse osmosis unit is provided having a second high pressure side and a second low pressure side for producing high purity product water.

Abstract: A method of purifying impure water to provide drinking water using an apparatus, the method comprising the steps of providing a microfiltration unit, a reverse osmosis unit and a CIP (clean-in-place) tank containing retentate interconnected to permit backflushing the microfiltration filter with retentate and continued or uninterrupted operation of the reverse osmosis unit by directing retentate thereto.

Abstract: A method for producing high purity product water using a three pass reverse osmosis system.

Abstract: A filtration device is provided for withdrawing permeate essentially continuously from a multicomponent aqueous substrate containing growing microorganisms in a reservoir. A vertical skein of fiber is scrubbed with coarse bubbles which emanate from a conversion baffle positioned under the skein. The substrate is aerated with fine bubbles in a size range small enough to transfer oxygen to the substrate efficiently. The baffle traps the fine bubbles and converts them to coarse bubbles which are effective to scrub the fibers. In the most preferred embodiment, the finished headers of the skein are derived from composite headers comprising a fixing lamina of resin in which the fibers are potted near their terminal ends, and a fugitive lamina of fugitive powdery material in which the terminal ends of the fibers are potted. The fugitive lamina is removed, preferably by dissolving the powder, e.g. finely divided common salt in water.

Abstract: A system of purifying water to remove at least one of natural organic matter, color, turbidity, bacteria, cysts and oocysts, viruses, arsenic compounds and insoluble impurities. The system comprises the steps of providing a body of water to be purified; controlling the pH of the body in a range of 5 to 8; and adding a coagulant to the body to provide a floc. The floc is maintained in the body in a concentration in the range of 1 to 6, for purposes of adsorbing at least one of the natural organic matter, color, turbidity and bacteria to provide treated water. Thereafter, a first portion of the treated water and floc is removed from the body of water. A submerged semi-permeable membrane is provided in the body of water for removing a second portion of the treated water. The membrane has a pore size in the range of 0.02 to 1 .mu.m to provide a permeate comprised of purified water and to provide a retentate containing the floc.

Abstract: A method for producing high purity product water using a three pass reverse osmosis system.

Abstract: A membrane filtration system which uses pump speed controllers to control flow rate and pressure during both the filtration cycle and the backwash cycle. The pump speed controllers operate by changing the frequency of AC current delivered to the pump motors, which changes the flow rate by changing the speed of the pump motor. The speed controllers operate by modulating the pump input power frequency in response to a signal from a flow or pressure signal received from a flow or pressure meter located on a liquid input pipe. This pump speed control method avoids the cyclical dampening patterns observed when trying to adjust pressure and/or flow rates by adjusting regulating valves. The system can also reduce or prevent formation of pressure spikes when switching from a filtration cycle to a backwash cycle, and vice versa. This reduces the likelihood of damage to the membrane from hydraulic pressure pulses.

Abstract: The outer surfaces of hollow fiber membranes in a skein, or a bank or cassette of stacked skeins, are kept essentially free of solids by maintaining a substantially uniform flow of a stream of coarse bubbles through each of plural orifices in an aerator disposed beneath the fibers. Aerators for skeins used in microfiltration of wastewater in a tank are periodically flushed by injecting flushing air into permeate returned to the tank over a short period. The air is injected into returning permeate for less than 1 minute, preferably less than 20 sec so as to produce discrete masses of water which are flowed laterally through the body of the aerator, cleaning its walls and maintaining the orifices essentially free from plugging.

Abstract: A filtration membrane for micro- or ultra-filtration is formed from a complex of PVDF and calcined .alpha.-alumina (".alpha.-Al") particles, in which complex the particles are reacted and dispersed. The suspended complex is then mixed with a hydrophilic polymer such as polyvinyl alcohol (40%-90% hydrolyzed) referred to herein as HPVA, which reacts with the complex imparting hydrophilicity to the polymer. The novel membrane provides about 50% higher specific flux than a membrane made with the same polymer but without the .alpha.-Al particles. Unexpectedly, the net flux is improved by treating the membrane with a solution of sodium hypochlorite which fails to remove the HPVA from the novel membrane but does remove it from the prior art membrane which does not contain the .alpha.-Al. The preferred membrane comprises a macroporous support coated on its outer surface with a thin tubular asymmetric semipermeable film of polymer containing less than about 50% by is weight of .alpha.-A1 particles.

Abstract: A filtration device is provided for withdrawing permeate essentially continuously from a multicomponent aqueous substrate containing growing microorganisms in a reservoir. A vertical skein of fiber is scrubbed with coarse bubbles which emanate from a conversion baffle positioned under the skein. The substrate is aerated with fine bubbles in a size range small enough to transfer oxygen to the substrate efficiently. The baffle traps the fine bubbles and converts them to coarse bubbles which are effective to scrub the fibers. In the most preferred embodiment, the finished headers of the skein are derived from composite headers comprising a fixing lamina of resin in which the fibers are potted near their terminal ends, and a fugitive lamina of fugitive powdery material in which the terminal ends of the fibers are potted. The fugitive lamina is removed, preferably by dissolving the powder, e.g. finely divided common salt in water.

Abstract: A gas-scrubbed vertical cylindrical skein of "fibers" has their opposed terminal portions held in headers unconfined in a modular shell, and aerated with a cleansing gas supplied by a gas-distribution means which produces a mass of bubbles serving the function of a scrub-brush for the outer surfaces of the fibers. The skein is surprisingly effective with relatively little cleansing gas, the specific flux through the membranes reaching an essentially constant relatively high value because the vertical deployment of fibers allows bubbles to rise upwards along the outer surfaces of the fibers. The effectiveness is critically dependent upon the length of each fiber in the skein. That length is in the range from at least 0.1% more than the fixed distance between opposed faces of the skein's headers, but less than 5% greater than the fixed distance.

Abstract: A process for purifying water by removing dissolved materials therefrom, the process capable of producing purified water having a resistivity in the range of 2 to 10 megohm-cm. The process comprises providing a water feed stream to be purified and adjusting the pH of the water feed stream to a basic water solution to drive the equilibrium of a first weakly ionized material to become ionized in the basic solution. The basic water solution is introduced to a high pressure side of a first reverse osmosis membrane module and water is passed through the first reverse osmosis membrane to provide a first retentate having ions therein from the first weakly ionized material concentrated therein and a first permeate depleted in ions from the first weakly ionized material. The pH of the first permeate is adjusted to an acidic water solution to drive the equilibrium of a second weakly ionized material to become ionized in an acidic solution.

Abstract: A process for purifying water including removing cations, anions and carbon dioxide and/or ammonia from water feed stream to produce high purity water having a resistivity of greater than 1 megohm-era comprising the steps of providing a water feed stream to be purified, the stream containing cations, anions and carbon dioxide and/or ammonia; introducing the water feed stream to a high pressure side of a first reverse osmosis membrane module; passing water through the first reverse osmosis membrane to provide a first retentate having cations and anions concentrated therein and a first permeate depleted in cations and anions and containing carbon dioxide and/or ammonia; adding the first permeate to a high pressure side, of a gas permeable hydrophobic membrane module; passing carbon dioxide and/or ammonia through the gas-permeable membrane from the first permeate in the high pressure side of the gas-permeable hydrophobic membrane to provide a carbon dioxide and/or ammonia permeate on a low pressure side of the h

Abstract: A vertical skein of "fibers", opposed terminal portions of which are held in headers unconfined in a modular shell, is aerated with a gas-distribution means which produces a mass of bubbles serving the function of a scrub-brash for the outer surfaces of the fibers. The membrane device is surprisingly effective with relatively little cleansing gas, the specific flux through the membranes reaching an essentially constant relatively high value because the vertical deployment of fibers allows bubbles to rise upwards along the outer surfaces of the fibers. Further, bubbles flowing along the outer surfaces of the fibers make the fibers surprisingly resistant to being fouled by build-up of deposits of inanimate particles or microorganisms in the substrate provided that the length of each fiber is only slightly greater than the direct center-to-center distance between opposed faces of the headers, preferably in the range from at least 0.1% to about 5% greater.

Abstract: A wastewater feed containing an ultimate BOD/COD ratio >0.6 is well-suited for especially acclimated thermophilic and/or caldo-active living micro-organisms ("hot cells") which thrive in an autothermal aerobic (ATA) reaction zone having an ATA bioreactor ("ATAB") operating at substantially ambient atmospheric pressure in combination with a MF or UF membrane filtration device from which a solids-free permeate may be withdrawn. This combination, of ATAB and membrane device is a "membrane bioreactor" (ATA MBR), which operates autothermally with a feed containing biodegradable organic materials having a BOD of at least 5,000 mg/L, preferably at least 10,000 mg/L (10 g/L) with a minor portion of "municipal" wastewater or domestic sewage. Operation of the ATAB, preferably in the thermophilic range from 45.degree. C.-75.degree. C., with constant HRT from 1 to 12 days, is contingent upon maintaining a stable population of live hot cells.

Abstract: Disclosed is an improved method for extending the useful life of a reverse osmosis membrane having a high pressure side and a low pressure side, the membrane used for separating soluble and sparingly soluble inorganic materials from an aqueous solution, the process comprising introducing an aqueous solution containing the soluble and sparingly soluble inorganic materials to the high pressure side of a reverse osmosis membrane and pressurizing the aqueous solution on said high pressure side to produce liquid on the low pressure side substantially free of said inorganic materials. Solution containing concentrated inorganic materials is transformed from the high pressure side of the reverse osmosis membrane to a high pressure side of a microfiltration membrane, and soluble inorganic materials transferred to the high pressure side of the microfiltration membrane was precipitated to provide solution containing particles of the inorganic materials.

Abstract: A hollow fiber membrane ("fiber") comprises a tubular macroporous support coated on its outer surface with a thin tubular asymmetric semipermeable film of polymer. The film, by itself, is non-self-supporting. The support itself is so flexible (flaccid) that it does not have a circular cross-section and collapses with finger pressure. Such a tube of knitted or woven braid no greater than 2.5 mm o.d., having interstitial voids which are non-uniformly shaped by the "ends" which are braided, is coated with a "dope" of polymer, then coagulated in a bath to form the film. Yet, after coating, the braided membrane can withstand up to 1500 psig in hydraulic compression forces before a straight-line relationship between flux and pressure begins to flatten out. The voids are relatively much larger than pores in the film. These voids are small enough to inhibit substantial penetration of the dope which lies superficially supported on the upper portion of the braid.

Abstract: A method and cleaning system is disclosed for cleaning the outer surface of a fouled microfiltration (MF) or ultrafiltration (UF) semipermeable hollow fiber membrane after its initial stable transmembrane flux has been decreased to an unacceptably low level. The method is specifically applicable to any fiber used to withdraw purified water from dirty water, particularly water containing organic matter including beneficial bacteria and/or undesirable inorganic salts, where the viability of the bacteria population is to be maintained. The membrane is cleaned by flowing a cleaning fluid, preferably a biocidal oxidative electrolyte having an oxidizing anion and an associated cation through the clean, permeate-side of the membrane, at low pressure no more than the bubble pressure breakthrough, usually <300 kPa (30 psig) for a MF or UF fiber.