Abstract: Drop-back of solids into the drum pool of a rotary microscreen is reduced by applying a limited gas pressure differential across an unsubmerged portion of the screen cloth. The pressure is not for the purpose of increasing the driving force, .DELTA.H, of the liquid passing through the cloth. For purposes of this disclosure, .DELTA.H is the pressure differential existing across the screen below the surface of both the drum pool and tank pool. In fact, assuming other factors remain equal, application of a gas pressure differential to an unsubmerged portion of the screen cloth, with consequent reduction in drum pool suspended solids concentration, will normally reduce .DELTA.H even though the gas pressure also acts on the surface of the drum pool. More significantly, the invention enables operation of a microscreen unit at increased flow capacity at a given .DELTA.H. Whatever pressure is applied, there will be some reduction of torque, bearing load and wear at any given .DELTA.H.

Abstract: A process and apparatus for decreasing the phosphorus content of waste water by means of contacting the waste water with the products of aqueous reaction with elemental iron, preferably subjecting the mixture to sequential aerobic and anaerobic conditions, and concentration of the suspended solids fraction which contains the major portion of the influent phosphorus in solid stable form, and separating the relatively clear liquid fraction therefrom.Contacting the waste water with products of the aqueous reaction with elemental iron may be brought about by recycling at least part of the separated solids through at least part of the process.

Abstract: Lengths of pipe are joined together in above- or below-ground telephone conduit systems by flexible sleeves having specified coefficient of friction, column expansibility and pull-out resistance and containing helically oriented high modulus reinforcement, bonded or encapsulated in elastomeric material. The resultant pipe assemblies represent a significant improvement over previously known cemented conduit-coupling arrangements. Pipe sections may be quickly and economically joined without field application of adhesive, to provide water-tight, pull-out-resistant joints which will accomodate significant bending moments and shearing forces.

Abstract: Lengths of "plain-end" pipe are joined together in underground sewer or drainage systems by flexible sleeves having a specified column expansibility and shear-resistance and containing high modulus helically oriented reinforcement, bonded or encapsulated in elastomeric material. The resultant pipe assemblies represent a significant improvement over previously known "plain-end" pipe-coupling arrangements and bell and spigot pipe assemblies. Pipe sections may be quickly and economically joined without inserting packing, to provide a water-tight, shear-resistant joint which will accomodate significant angular misalignment and circumferential variation. Even if lubricant is placed on the inner surfaces of the flexible sleeves to reduce assembly forces, the resultant pipe assemblies still exhibit more than adequate resistance against shear loads and water infiltration.

Abstract: Filtration in an internal rotary filter system is improved by externally impacting the filter screen as it rotates with a programmed spray of liquid that is varied from a relatively low to a relatively high pressure. In certain instances, this programmed spray is controlled by an electric timer circuit so arranged that the high pressure spray is on for a period of time which does not too unduly burden the system with fluid, but which is sufficient period of time to prevent slime formation on the screen. This can for instance keep the screen free of slime when no germicidal agent (e.g. Cl.sub.2) is employed.