WO2008132288A1

WO2008132288A1 - Screenings washer

Info

Publication number: WO2008132288A1
Application number: PCT/FI2008/050233
Authority: WO
Inventors: Marika Voittola; Jukka KÖYKKÄ
Original assignee: Preseco Oy
Priority date: 2007-04-27
Filing date: 2008-04-25
Publication date: 2008-11-06
Also published as: FI7603U1; FIU20070172U0

Abstract

The present invention relates to an apparatus for removing organic matter from wastewater screenings in the purification of wastewaters. Organic matter that is important for the biological wastewater purification process will be retained in the process by removing from the screenings also organic constituents by washing. The screenings washer (1) of the invention preferably comprises an inlet funnel (2) for receiving wastewater and a screw conveyor (3) for transferring the wastewater and for separating the screenings. For reject removal the apparatus also comprises a water discharge opening (4) and a screenings outlet funnel (5). The screenings are treated in a water permeable wash drum (10). The wash drum (10) is surrounded by a substantially waterproof frame tube (11), the wash drum (10) and the frame tube (11) delimiting between them a flow space (12) that comprises wash nozzles (14) directed towards the wash.

Description

SCREENINGS WASHER

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an apparatus in accordance with the preamble of claim 1. This apparatus is used in purification of wastewaters, in particular for removing organic matter from wastewater.

[0002] It is previously known to remove solid matter from the wastewater, for instance, by using sand separators, screens and drum strainers.

[0003] For instance, when step screens are employed, liquid is separated from screenings by filtration with the assistance of a screen mat, whereby a large part of organic matter in the wastewater adheres to the screenings.

[0004] In a drum strainer, in turn, wastewater is first conveyed to a screen in the apparatus, where screenings are washed out and organic matter is separated to some extent, but because washing out is not the main object of these solutions, the results are modest.

[0005] Residual organic matter in the screenings cause considerable odour problems as they mix with the screenings to be removed from the purification process. On the other hand, this organic matter is an important part of a biological wastewater purification process, and consequently it should stay as long as possible in this process.

BRIEF DESCRIPTION OF THE INVENTION

[0006] The object of the present invention is thus to develop an apparatus that would provide a novel solution to above-mentioned problems posed by drawbacks in the prior art.

[0007] In particular, the present problems are solvable by combining the characteristics in the manner disclosed in the characterizing part of claim 1.

[0008] Preferred embodiments of the invention are disclosed in the dependent claims.

[0009] The invention is based on the idea that, apart from liquid removed by filtration, also organic matter would be removed from screenings by washing.

[0010] Considerable advantages are achieved by the apparatus of the invention. So, it will provide a considerably higher degree of purification of the screenings, whereby odour problems caused thereby will be reduced. [0011] At the same time, nutrients consisting of organic matter in the wastewater will be returned to the rest of the purification process.

[0012] This advantageous end result is provided by relatively simple means. By adding water and enhancing the stirring of wastewater it is possible to improve detachment of organic matter from the screenings considerably.

[0013] Water jets generated by wash nozzles of the present invention prevent, at the same time, screenings treated in the apparatus and the organic matter from adhering to the wash drum. This ensures efficient and trouble-free use of the apparatus.

[0014] Air nozzles of the present invention also substantially enhance separation of organic matter from the screenings, through stirring provided by feeding of air.

[0015] Because some of the material is returned to the purification process, the amount of screenings is naturally reduced, whereby further processing costs of this problematic waste fraction will at the same time reduce.

[0016] The apparatus of the invention may also be utilized as a screw conveyor for transferring screenings onto a press employed in the purification process. In this manner it is possible to avoid acquisition of a separate device.

[0017] Other advantages to be achieved with the invention will be described below in connection with a detailed description of particular embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In the following, a preferred embodiment of the invention will be described in greater detail with reference to the attached drawing, in which Figure 1 is a side view of a screenings washer, Figure 2 is a top view of the screenings washer of Figure 1 , Figure 3 is a longitudinal section of the screenings washer of Figure

1 ,

Figure 4 is a cross section at point A - A of Figure 3 and Figure 5 is an alternative cross section at point A - A of Figure 3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0019] A preferred embodiment of the present screenings washer is described below with reference to the above-mentioned figures. In this case the screenings washer comprises structural components provided in the figures with reference numerals that correspond to those used in this description.

[0020] When Figures 1 and 3 are studied, it is possible to discern the main parts of the present screenings washer 1. The apparatus comprises, for instance, an inlet funnel 2 receiving the wastewater to be treated in the purification process. Therefrom the wastewater to be treated is conveyed with a screw conveyor 3 towards a water discharge opening 4 and a screenings outlet funnel 5 locating opposite the inlet funnel.

[0021] In accordance with Figures 2 and 3, the screw conveyor 3 comprises a screw helix 6 extending from the inlet funnel 2 to the outlet funnel 5. The screw conveyor is attached both to the inlet funnel and to the outlet funnel through flanges 7 and 8 preventing water flow, whereby a screw helix part 6a on the inlet funnel side guides the wastewater arrived in the inlet funnel to pass by the flange into a washing space 9 of the screw conveyor. The wastewater with its constituents is transferred in the washing space, advantageously through a screw helix part 6b, towards the outlet funnel 5. The screenings are further guided into the outlet funnel with a screw helix part 6c past the flange 8. The flange prevents the access of liquid substances into the outlet funnel. These liquid substances are to be removed from the screw conveyor through a water discharge opening 4 locating at the end of the screw conveyor on the outlet funnel side.

[0022] In standard use position the screenings washer 1 is arranged at an angle of 20 to 40 degrees to a vertical plane. In that case the water collected in the washing space 9 and separated from the screenings fills most part of the washing space and discharges as an overflow through the water discharge opening 4.

[0023] Because an amount of liquid extending up to the discharge opening 4 is collected in the washing space, the screenings will be mixed with a larger amount of water than previously. The mixing, in turn, increases the contact surface between the screenings and the water circulating in the washing space, and consequently contributes to the detachment of organic matter adhering to the surface of the screenings. As can be observed in Figures 3 - 5, the screw conveyor 3 comprises a double jacket structure. So, the screw helix 6 is surrounded by a wash drum 10, which in turn is surrounded at a distance by a frame tube 11. The wash tube is advantageously arranged to be permeable to water, whereby it is provided, for instance, with perforation, as sche- matically shown in Figure 3, or it is manufactured of a material suitable for this purpose. The frame tube is substantially waterproof, whereby the wash drum and the frame tube delimit a flow space 12 between them. As wastewater is treated, the screenings thus accumulate in the washing space 9 delimited by the wash drum, when the liquid collected onto the screw conveyor extends up to the flow space, and is discharged therefrom through the water discharge opening 4.

[0024] Separation of the screenings and the organic matter adhering thereto is further enhanced by interconnecting the wash drum 10 and the screw helix 6 substantially unrotatably. The screw helix is mounted on bearings at the opposite ends of the screenings washer 1 and advantageously also supported to the frame tube 11 at the flanges 7 and 8. As the wash drum and the screw helix are interconnected, the rotation of the screw helix with a power source 13 makes them rotate in relation to the frame tube. The motion of the screw helix and the wash drum further stir the screenings and the liquid and thus detach more organic matter from the screenings.

[0025] By adding in the flow space 12 wash nozzles 14 directed towards the wash drum 10 it is possible to wash out the screenings in the wash drum with one or more water jets to enhance the detachment. At the same time the wash nozzles ensure that there is a sufficient amount of water present in the washing space 9.

[0026] It appears from Figure 4 that wash nozzles 14 are arranged on the cross section of the screw conveyor 3 such that they direct the water jets into the wash drum from at least two different directions. Even though in the figure the wash nozzles are arranged on both sides of the vertical normal of the wash drum, there is no objection to place the wash nozzles in some other manner, for instance, in opposing positions. In addition, these wash nozzles may be arranged in the screw conveyor at two or more cross sections of the wash drum 10 and the frame tube 11 concentrically surrounding each other in the direction of the central axis 15.

[0027] On one hand, the wash nozzles 14 thus maintain the liquid level in the space confined by the frame tube 11. On the other hand, the liquid flow produced by the wash nozzles washes out the screenings and detaches organic matter therefrom. The liquid flow also makes sure that the perforation of the wash drum will not be clogged by removing screenings accumulated on the inner surface of the wash drum. [0028] It is also possible to increase the motion of the screenings in the washing space by arranging stirring members 17 as shown in Figure 5 on the inner surface 16 of the wash drum on the side of the screw helix so as to stir the wastewater in the wash drum. The stirring member of this kind comprises means that protrude from the inner surface of the wash drum towards the central axis 15 of the screw conveyor. At their simplest, these means consist of angle iron pieces substantially in the direction of the central axis of the screw conveyor. In the same way as the wash nozzles 14, these stirring members 17 may be arranged at least at two different points on the cross section of the wash drum 10. Into the screw conveyor 3 and the washing space 9 therein it is also possible to introduce air or some other gaseous substance, for instance, by means of particular air nozzles 18, which contribute to the mixing of the screenings. These air nozzles are advantageously arranged in the apparatus at the end thereof on the inlet funnel side, for instance, as shown in Figure 3.

[0029] Even though the figures indicate that the wash drum 10 and the frame tube 11 are arranged substantially concentrically to the screw conveyor 3, this does not mean that other embodiments could not be utilized in the implementation of this or some other structural solution presented. Thus, it is apparent to a person skilled in the art that as technology advances the basic idea of the above-described solution may be implemented in a variety of ways. The presented solution and the embodiments thereof are thus not limited to the above-described examples, but they may vary within the scope of the claims.

Claims

1. A screenings washer (1) comprising an inlet funnel (2) for receiving wastewater, a screw conveyor (3) for transferring the wastewater and for separating screenings and a water discharge opening (4) and a screenings outlet funnel (5), characterized in that the screw conveyor (3) comprises a screw helix (6) extending from the inlet funnel (2) to the outlet funnel (5) and surrounded by a water permeable wash drum (10) which, in turn, is surrounded by a substantially waterproof frame tube (11) such that the wash drum (10) and the frame tube (11) delimit between them a flow space (12), which comprises wash nozzles (14) directed towards the wash drum (10).

2. The screenings washer (1) of claim 1, characterized in that the wash drum (10) and the frame tube (11) are arranged substantially concentrically on the screw conveyor (3).

3. The screenings washer (1 ) of claim 1 or 2, characterized in that wash nozzles (14) are arranged on the cross section of the screw conveyor (3) such that they direct water jets in the wash drum (10) from at least two different directions.

4. The screenings washer (1) of any one of the preceding claims, characterized in that wash nozzles (14) are arranged in the direction of the central axis (15) of the screw conveyor (3) at two or more cross sectional points.

5. The screenings washer (1) of any one of the preceding claims, characterized in that the wash drum (10) and the screw helix (6) are interconnected substantially unrotatably while they are arranged to rotate in relation to the frame tube (11).

6. The screenings washer (1) of claim 5, characterized in that the inner surface (16) of the wash drum (10) on the side of the screw helix (6) is provided with stirring members (17) for stirring the wastewater in the wash drum.

7. The screenings washer (1) of claim 6, characterized in that the stirring member (17) comprises members protruding from the inner surface (16) of the wash drum (10) towards the central axis (15) of the screw conveyor (3).

8. The screenings washer (1) of claim 7, characterized in that the stirring member (17) comprises angle iron pieces substantially in the direction of the central axis (15) of the screw conveyor (3).

9. The screenings washer (1) of any one of claim 6, 7 or 8, c h a r - acterized in that the stirring members (17) are arranged at least at two different points on the cross section of the wash drum (10).

10. The screenings washer (1) of any one of the preceding claims, characterized in that the screenings washer (1) comprises air nozzles (18) that are arranged to introduce gaseous substance into the screw conveyor (3).