METHOD AND APPARATUS FOR TREATING A LIQUID MIXTURE

Abstract: Treating a liquid mixture to separate a clarified fraction therefrom leaving a concentrated sludge fraction involves injecting a flocculent material into the liquid mixture; and inletting the liquid material and the floc­ culent material tangentially into a vertical tank (12) having a perforated plate (20) spaced from its upper end dividing the tank (12) into an upper chamber (12a) and a lower chamber (12b), to produce a flow in the lower chamber (12b) having a rotational velocity in the hori­ zontal direction adjacent the outer periphery of the lower chamber (12b), and a lower rotational velocity in the horizontal direction adjacent the center of the lower chamber (12b). The holes (20a) in the perforated plate (20) define reduced-area passages from the lower chamber (12b) to the upper chamber (12a) producing a vertical flow of low velocity in the lower chamber (12b) and of higher velocity through the passages (20a) in the perforated plate (20).

Description: The present invention relates to a method and apparatus for treating a liquid mixture in order to separate a clarified fraction therefrom, leaving a concentrated sludge fraction. The invention is particularly applicable for treating municipal or industrial waste water in order to enable such waste water to be reused for municipal, industrial or agricultural purposes. Municipal or industrial waste water, as well as water from rivers or lakes, must first be treated in order to remove substances which may be harmful, or which cause bad taste or odour. Many techniques are known for this purpose. One technique is a sedimentation technique wherein the solid particles or other heavy substances are permitted to separate by sedimentation from the liquid mixture, but the conventional sedimentation technique requires a relatively long period of time for the solid particles or heavy substances to settle. In order to increase the rate at which the solid particles settle, a flocculent material may be added to the liquid mixture, the flocculent material tending to flock or agglomerate with the solid particles thus enhancing the settling of the solid particles. However, relatively long periods of time are required even when using such flocculent materials. An object of the present invention is to provide a method, and also an apparatus, for treating a liquid mixture in order to accelerate this process of separating the clarified fraction from the concentrated sludge fraction (the agglomerated solid particles). According to the present invention, there is provided a method of treating a liquid mixture to separate a clarified fraction therefrom leaving a concentrated sludge fraction, comprising: injecting a flocculent material into the liquid mixture; inletting the liquid material and the flocculent material tangentially into a vertical tank having a perforated plate spaced from its upper end dividing the tank into an upper chamber and a lower chamber, to produce a flow in said lower chamber having a rotational velocity in the horizontal direction adjacent the outer periphery of said lower chamber, and a lower rotational velocity in the horizontal direction adjacent the center of the lower chamber, the holes in said perforated plate defining reduced-area passages from the lower chamber to the upper chamber producing a vertical flow of low velocity in the lower chamber and of higher velocity through said passages in the perforated plate, whereby the flocculent material flocks with most of the solid particles in the liquid mixture at the lower part of the lower chamber and with the remaining solid particles at the upper part of the lower chamber, such that a clarified fraction passes through the holes in the plate to the upper chamber, leaving a concentrated sludge fraction in the lower chamber; outletting the clarified liquid fraction from the upper chamber; and outletting the concentrated sludge fraction from the lower chamber. The invention also provides apparatus for treating a liquid mixture in accordance with the above method to separate a clarified fraction therefrom, leaving a concentrated sludge fraction. In the preferred embodiment of the invention described below, the perforated plate is a flat horizontal plate; also, the clarified fraction is outletted radially from the upper chamber; further the concentrated sludge fraction is outletted through a conical funnel at the bottom of the lower chamber. Further features and advantages of the invention will be apparent from the description below. The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: Fig. 1 illustrates one form of apparatus constructed in accordance with the invention; and Fig. 2 is a top plan view of the apparatus of Fig. 1. The apparatus illustrated in the drawings is intended particularly for treating municipal or industrial waste water in order to make it suitable for reuse for municipal, industrial or agricultural purposes. The waste water is collected in a reservoir 2 and is pumped by a pump 4 via a feed tube 6 to a flocculent material mixing vessel 8 and then to the inlet 10 of a sedimentation tank 12. There, the water is separated into a clarified fraction removed via an outlet 14 at the upper end of the tank, and a concentrated sludge fraction removed via an outlet 16 at the lower end of the tank. The flocculent material is injected from a source 18 into the raw feed water passing through the feed tube 6 so that the two are mixed in vessel 8 before the mixture is introduced into the sedimentation tank 12. The mixture of the raw feed water and the flocculent material is introduced via inlet 8a at the upper end of vessel 8, and is removed via its outlet 8b at the bottom of the vessel. Sedimentation tank 12 is a large, vertical, cylindrical tank supported above the ground by legs 19. The tank includes a flat perforated plate 20 fixed horizontally at the upper end of the tank so as to divide its interior into an upper chamber 12a and a lower chamber 12b. The clarified water outlet 14 at the upper end of tank 12 is above perforated plate 20, to communicate with the upper chamber 12a, and, as shown in Fig. 2, extends radially of the upper chamber 12a. The concentrated-sludge outlet 16 is at the bottom of the lower chamber 12b and is provided with a conical funnel 22 so as to direct the concentrated sludge settling at the bottom of the chamber through outlet 16. The inlet 10 into the tank 12 is approximately midway between the perforated plate 20 and the upper end of conical funnel 22. As shown particularly in Fig. 2, the inlet 10 is tangential to the tank 12 so as to impart a rotational flow of the mixture of raw feed water and flocculent material when introduced into the lower chamber 12b. This flow into the lower chamber 12b has a rotational velocity in the horizontal direction adjacent the outer periphery of the lower chamber, and a lower rotational velocity in the horizontal direction adjacent the central axis 24. Perforated plate 20 is formed with a plurality of holes 20a defining reduced-area passages from the lower chamber 12b to the upper chamber 12a. These reduced-area passages produce a vertical flow of higher velocity through the passages 12a than in the lower chamber 12b, tending to cause the flocculent material, injected from source 18, to flock or aggregate with the solid particles or other heavy substance in the raw feed water in the lower chamber and to separate in the lower chamber. The higher velocity of the liquid at the mouth of the holes 20a, and the reduced-area of the passages for the liquid through the holes which brings the remaining particles closer together, increases the flocculation efficiency, and thereby produces a clarified fraction which passes through these holes into the upper chamber 20 and out through outlet 14. The aggregates of flocking material, solid particles and other heavy substances in the raw feed water, settle in the form of a concentrated sludge fraction directed by funnel 22 to the outlet 16. It has been found that the apparatus illustrated in the drawings is effective to substantially reduce the time for separating the raw feed water into the clarified fraction removed via outlet 14 and the concentrated sludge fraction removed via outlet 16. For example, it has been found that a tank of 1.20 meters in diameter and a volume of 2.5 cubic meters is able to treat raw feed water having 15 grams per liter of solids at a rate of 30 cubic meters per hour.

Claims: A method treating a liquid mixture to separate a clarified fraction therefrom leaving a concentrated sludge fraction, comprising: injecting a flocculent material into the liquid mixture; inletting the liquid material and the flocculent material tangentially into a vertical tank having a perforated plate spaced from its upper end dividing the tank into an upper chamber and a lower chamber, to produce a flow in said lower chamber having a rotational velocity in the horizontal direction adjacent the outer periphery of said lower chamber, and a lower rotational velocity in the horizontal direction adjacent the center of the lower chamber; the holes in said perforated plate defining reduced-area passages from the lower chamber to the upper chamber producing a vertical flow of low velocity in the lower chamber and of higher velocity through said passages in the perforated plate, whereby the flocculent material flocks with most of the solid particles in the liquid mixture at the lower part of the lower chamber and with the remaining solid particles at the upper part of the lower chamber, such that a clarified fraction passes through the holes in the plate to the upper chamber, leaving a concentrated sludge fraction in the lower chamber; outletting the clarified liquid fraction from the upper chamber; and outletting the concentrated sludge fraction from the lower chamber. The method according to Claim 1, wherein said clarified fraction is outletted radially from the upper chamber. The method according to Claim 2, wherein the liquid mixture is inletted into the vertical tank approximately midway between the perforated plate and the upper end of said conical funnel at the bottom of the lower chamber. The method according to any one of Claims 1-3, wherein the horizontal velocity of the rotational flow in the lower chamber is in the order of 50 cm/sec at the outer periphery of the lower chamber, and approximately zero at the center of the lower chamber. Apparatus for treating a liquid mixture to separate a clarified fraction therefrom leaving a concentrated sludge fraction, comprising: a vertical tank having a perforated plate spaced from its upper end dividing the tank into an upper chamber and a lower chamber; means for injecting a flocculent material in the liquid mixture; a tangential inlet in said lower chamber of the vertical tank for inletting the liquid mixture and flocculent material tangentially into the lower chamber to produce a flow in said lower chamber having a rotational velocity in the horizontal direction adjacent to the outer periphery of said lower chamber, and a lower rotational velocity in the horizontal direction adjacent to the center of said lower chamber; the holes in said perforated plate defining reduced-area passages from the lower chamber to the upper chamber producing a vertical flow of low velocity in the lower chamber and of higher velocity through said passages, whereby the flocculent material flocks with most of the solid particles in the liquid mixture at the lower part of the lower chamber and with the remaining solid particles at the upper part of the lower chamber, such that a clarified fraction passes through the holes in the plate to the upper chamber, leaving a concentrated sludge fraction in the lower chamber; an outlet in the upper chamber for outletting the clarified fraction therefrom; and an outlet in the lower chamber for outletting the concentrated sludge fraction therefrom. The apparatus according to Claim 5, wherein said perforated plate is a flat horizontal plate. The apparatus according to either of Claims 5 or 6, wherein said outlet in the upper chamber for outletting the clarified fraction therefrom extends radially of the upper chamber. The apparatus according to any one of Claims 5-7, wherein said outlet in the lower chamber outletting the concentrated sludge fraction therefrom comprises a conical funnel at the lower end of the lower chamber. The apparatus according to Claim 8, wherein said tangential inlet into the lower chamber is located approximately midway between said perforated plate and the upper end of said conical outlet at the lower end of the lower chamber. The apparatus according to any one of Claims 5-9, wherein said means for injecting a flocculent material into the liquid mixture comprises: a mixing vessel having an inlet pipe connected to the source of the liquid mixture, and an outlet pipe connected to the tangential inlet of the tank; and an injector connected to said inlet pipe for injecting the flocculent material into the liquid mixture before it enters said mixing vessel such that the flocculent material is mixed with the liquid mixture before the latter is introduced into said tangential inlet of the vertical tank.

Inventors: ELI, NISSIM, MARRACHE, ALBERT
Applicants: ODIS IRRIGATION EQUIPMENT LTD.
Application year: 1990
Main classification: C02F1
IPC codes: C02F1