Clarifiers (also known as “settlers”) are used in attempts to efficiently remove certain materials and particles (herein “materials”) from liquid. These materials are generally suspended in the liquid and can be removed under the force of gravity when the volumetric flow rate of the liquid is substantially reduced, as in an individual very low flow, or quiescent, flow path (or settling flow path) in the clarifier. Since these materials are generally solid and are said to “settle” out of the liquid, they are referred to as “settleable solids”. Such settleable solids may include naturally occurring materials (e.g., clay, silt, sand and dirt), chemical precipitants and biological solids. The word “solids” as used herein to describe the present invention refers to such settleable solids.
Clarifiers are used, for example, in water and waste water treatment plants. In water treatment, the water drawn from a water supply has various non-settleable colloidal solids therein. When mixed with chemicals, the colloidal solids and chemicals agglomerate to form solids. In waste water treatment, the solids include organic solids, among other wastes. Water and waste water are treated in clarifiers to remove such solids, thereby making the water clear and suitable for use, reuse, or for further treatment, such as tertiary treatment. The word “liquid” as used herein to describe the present invention refers to water and waste water.
Water and waste water clarifiers attempt to create the settling flow paths, with each individual settling low path having a very low volumetric flow rate (e.g., in a range of from about two to six gallons per minute (GPM). The attempt is to promote maximum settlement of solids to the bottom of the clarifiers for a particular total volumetric flow rate of water or waste water into the entire settler, and thus attempt to promote high settling efficiency. The attempts include clarifiers configured with tubes or flat plates mounted in a basin. Mounting exemplary plates at fixed angles relative to the surface of the liquid forms multiple ones of the settling flow paths in the basin. A goal is for the liquid containing the solids to flow upwardly in each particular settling flow path between such plates (referred to as “settling flow”) at a very low flow rate that allows sufficient time for most of the solids to settle onto one of the plates. Ideally, the solids then slide down the plate to the bottom of the basin for collection. After the solids have settled, the liquid without the settled solids is referred to as “clarified liquid”. The clarified liquid flows upwardly past the plates and out of an open top (or “clarifier exit”) of each settling flow path. Such open top is between and at the top of the exemplary adjacent plates, or at the top of an exemplary tube.
Generally, the clarified liquid from each of the separate settling flow paths may combine in a trough above the clarifier. The combined clarified liquid flows in the trough to a trough outlet at an end of the basin for exit from the basin. However, problems have been experienced in the use of such troughs that receive the settling flows from the individual settling flow paths of the clarifiers. For example, it has been observed that in many instances clarifier efficiencies have been significantly less than planned or expected based on design criteria.
In view of the forgoing, there is a need to achieve clarifier efficiencies that are as planned or expected based on design criteria, e.g., planned as high settling efficiencies. There is thus a need for avoiding reduction of clarifier efficiency and for avoiding the attendant reduced settling of solids for a given inflow of solids and liquid to the settling flow paths. There is also a related need to avoid having more of the solids flow out of the settling flow paths in low efficiency clarifiers than in high efficiency clarifiers.