GB2436103A

GB2436103A - Trickling filter with wind assisted motion

Info

Publication number: GB2436103A
Application number: GB0605516A
Authority: GB
Inventors: Vaughan Hobson
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-03-18
Filing date: 2006-03-18
Publication date: 2007-09-19
Also published as: GB0605516D0

Abstract

A trickling filter unit comprises a bed of filter media 2 over which are located a plurality of distribution arms 3 connected to a rotatable hub 4. At least one of the distribution arms 3 has a wind vane 6 pivotally connected thereto. The vane 6 can pivot about an axis 8 parallel to the longitudinal axis 10 of the arm 3 it is connected to, between a substantially horizontal rest position and a raised position. When moving with the wind, the vane 6 is raised and thereby contributed to the force rotating the arms 3, but has a negligible wind resistance when moving into the wind. Rotation of the vane 6 beyond the raised position is prevented as a lower portion 12 of the vane 6 contacts the arm 3.

Description

IMPROVEMENTS TO TRICKLING FILTER UNITS

The present invention relates to trickling filter units such as those commonly utilized in sewage treatment works.

In a trickling filter unit, liquid sewage is distributed over a bed of filter media by distribution arms that rotate above the bed. The distribution arms are tubular and the sewage flows along the arms and then trickles out onto the filter media through a series of holes formed along the length of the arms. Typically, two or four such arms are connected to a central hub and the jet reaction of the sewage leaving the arms causes them to rotate. In this way, the sewage is evenly distributed over the filter media in the bed.

Occasionally, the arms may be driven by an electric motor that is usually located near to the hub of the arms.

One problem that arises with this arrangement is that in strong wind conditions, the arms may be prevented from rotating. The jet reaction forces of the sewage leaving the arms can be insufficient to overcome the forces generated by the wind passing the arms. In extreme cases, motor driven arms may also be affected in this way and prevented from rotating. If uneven distribution of the sewage over the bed occurs it is detrimental to the efficiency of the biological processes in the bed and can result in a poor final effluent leading to pollution of rivers and water courses.

In order to overcome the aforementioned problem, it has been proposed to harness any available wind forces and to utilize them to drive the rotating arms. GB 2156442 describes such an arrangement wherein vertically pivoting vanes are fixed to each of the distribution arms of a filtering unit. The vanes are each adapted to rotate through angles of up to 900 at a maximum of 45 to the arm. However, this arrangement has proved to be unsatisfactory because the vanes always have a wind resistance, even when in a passive position. The drag on the passive distribution arm is exaggerated because the arm is traveling into the wind, thereby increasing the relative wind speed. The differential resistance between the active vane or vanes and the passive vane or vanes is therefore reduced.

The object of the present invention is to provide a trickling filter unit which overcomes or substantially mitigates the aforementioned problem.

According to a first aspect of the present invention there is provided a trickling filter unit comprising a bed of filter media over which is located a plurality of distribution arms that are connected to a rotatable hub in order that liquid flowing through the hub and down the arms can be trickled out over the surface of the bed, and at least one wind vane arrangement connected to one of the distribution arms such that a vane of the arrangement can pivot about an axis substantially parallel to the longitudinal axis of the distribution arm between an at rest position wherein the vane lies in a plane substantially parallel to said axis of the distribution arm and an in use position wherein it is pivoted out of said plane.

Hence, in the present invention unlike the prior art arrangement, when the vane is in use in its at rest position it can assume a near horizontal attitude and have a negligible wind resistance when rotating into the wind.

Preferably, the vane is restrained from pivoting through more than 900 between its at rest position and its in use position by means of a detent.

Preferably also, the vane is connected to a spindle that is pivotally mounted to the distribution arm by at least one bracket.

Preferably also, the spindle is located in or in the vicinity of the tangential plane touching the uppermost part of the arm.

Preferably also, the spindle is located inboard of a leading edge of the vane with respect to the intended direction of rotation of the arm such that at least a portion of vane between the spindle and the leading edge can contact part of the outer surface of the distribution arm when the vane is pivoted out of its rest position such that the distribution arm itself thereby forms the detent.

Preferably also, the spindle is located on a leading side of a vertical plane passing through the longitudinal axis of the arm with respect to the intended direction of rotation of the arm.

Preferably also, the vane is substantially rectangular in shape with its longer sides positioned parallel to the spindle.

Preferably also, the unit comprises at least two distribution arms arranged in-line over the bed of the filter media and each provided with a wind vane arrangement. Advantageously, four distribution arms are provided in a cruciform arrangement and each of the arms is provided with a wind vane arrangement.

According to a second aspect of the present invention there is provided a wind vane arrangement for a trickling filter unit according to the first aspect of the present invention and comprising a vane connected to a spindle that is pivotally mounted on at least one bracket adapted for connection to a distribution arm of the unit such that the vane can pivot about an axis substantially parallel to the longitudinal axis of the distribution arm.

The present invention will now be described with reference to the accompanying drawings, in which:-Fig. 1 is a perspective schematic view of a trickling filter unit in accordance with the invention; Fig. 2 is a schematic transverse cross-section through a distribution arm of the trickling filter unit shown in Fig. 1 to an enlarged scale and showing the position of a vane of a wind vane arrangement forming part of the unit when in a rest position; Fig. 3 is a view similar to Fig. 2 but showing the vane in an in-use position; Figs 4 to 6 are plan, side and end elevations of the wind vane arrangement.

A trickling filter unit 1, as shown in Fig. 1, comprises a bed of filter media 2 over which is located, in a cruciform arrangement, four hollow distribution arms 3. The arms 3 are connected to a rotatable hub 4 through which liquid flows into the arms 3 whence it can be trickled out over the surface of the bed 2 through a series of holes 5 formed along one side of each of the arms 3. In a conventional fashion, the jet reaction of the liquid leaving the arms 3 causes them to rotate but they may also be driven by an electric motor (not shown). In Fig. 1, the holes 5 are located such that the arms 3 and the hub 2 rotate in a clockwise direction when viewed from above.

Each of the arms 3 is provided with a wind vane arrangement 6. This arrangement 6, as shown in Figs. 4, 5 and 6, comprises a substantially rectangular vane 7 which is connected to a spindle 8. The spindle 8 is pivotally connected at each end to a bracket 9 that is adapted for connection to a distribution arm 3 of the unit 1 such that the vane can pivot about an axis substantially parallel to the longitudinal axis 10 of the distribution arm.

In most applications it is expected that the vane will be approximately 200 mm wide by 400 mm long with its longer sides positioned parallel to the longitudinal axis of the spindle 8.

As shown in Figs. 2 and 3, the brackets 9 are connected to the arm 3 in a position wherein the spindle 8 is located on a leading side of a vertical plane passing through the longitudinal axis 10 of the arm 3 with respect to the intended direction of rotation of the arm, as indicated by the arrow labeled motion'. The spindle 8 is preferably located in or in the vicinity of the tangential plane touching the uppermost part of the arm 3. Assuming that the arms 3 are mounted horizontally, then this plane will also be horizontal. Hence, as shown in Fig. 2, when a wind blows in a direction substantially opposite to the direction of motion, as shown by the arrow labeled wind', the vane 7 assumes an at rest' position at or near the horizontal above the upper surface of the distribution arm 3. The vane 7 therefore has a negligible wind resistance. However, if the vane 7 is caught by a wind blowing in substantially the same direction as the direction of motion, as shown in Fig. 3, the air flowing around the distribution arm 3 lifts the vane 7 to a near vertical position. In this in use' position, the vane 7 increases the effective surface area of the distribution arm 3 thus increasing the resistance and hence contributes to the forces causing the rotation of the arm 3.

The spindle 8 is located inboard of a leading edge ii of the vane 7 with respect to the direction of rotation of the arm 3 such that at least a portion 12 of vane between the spindle 8 and the leading edge 11 can contact part of the outer surface of the distribution arm 3 when the vane 7 is pivoted out of its rest position by the wind, as shown in Fig. 3. The distribution arm 3 thereby forms a detent which restrains the vane 7 from pivoting through more than 900 between its at rest position and its in use position and limits rotation of the vane 7 past a vertical position in order to ensure that the vane 7 remains in a position of near maximum wind resistance. In an alternative embodiment (not shown) a detent that is connected to and projects from the distribution arm 3 can be provided for the same purpose. In this way, the vane 7 can either fall back to the at rest position under its own weight or be blown back by the wind when the arm 3 has rotated to a position where it is again travelling into the wind.

In this illustrated embodiment, the unit 1 comprises four identical arms 3 in a cruciform arrangement but it will be appreciated that any number of such arms 3 could be provided. Advantageously, however, there are always at least two distribution arms 3 arranged in-line over the bed of the filter media 2, each provided with a wind vane arrangement 6. Also, more than one wind vane arrangement 6 can be fitted to each arm 3 of a unit 1, particularly in locations which tend to be subject to high wind speeds.

The advantage of the present invention over the prior art is that in the present case the arms 3 can be kept rotating even in high wind conditions because they increase the effective surface area of the distribution arm or arms 3 that are rotating in the same direction as the wind whilst having a minimal drag effect on the arm or arms 3 that are rotating into the wind.

Additional advantages are that the shape and size of the vane 7 is not critically important, though it will affect the efficiency and the performance of the arrangement 6 but it is advantageous that larger filter units can be fitted with wind vane arrangements 6 that incorporate larger vanes or are fitted with more than one arrangement 6 per arm 3.

Advantageously, the shape, dimensions and weight of the vane 7 should be selected so that the wind can rotate the vane 7 to the in use position only when required, i.e. only when the wind is strong enough to affect the efficient rotation of the distribution arms 3.

The wind vane arrangement 6 can be mounted at any location along a distribution arm 3, subject to existing fixtures of the arm not being adversely affected by the vanes and vice versa. However, it will be appreciated that the nearer to the hub 4 of the arms 3, the smaller the rotational forces that can be created by the arrangement 6.

Claims

CLAIMS

1. A trickling filter unit comprising a bed of filter media over which is located a plurality of distribution arms that are connected to a rotatable hub in order that liquid flowing through the hub and down the arms can be trickled out over the surface of the bed, and at least one wind vane arrangement connected to one of the distribution arms such that a vane of the arrangement can pivot about an axis substantially parallel to the longitudinal axis of the distribution arm between an at rest position wherein the vane lies in a plane substantially parallel to said axis of the distribution arm and an in use position wherein it is pivoted out of said plane.

2. A unit as claimed in Claim 1, wherein the vane is restrained from pivoting through more than 900 between its at rest position and its in use position by means of a detent.

3. A unit as claimed in Claim 1 and Claim 2, wherein the vane is connected to a spindle that is pivotally mounted to the distribution arm by at least one bracket.

4. A unit as claimed in Claim 3, wherein the spindle is located in or in the vicinity of the tangential plane touching the uppermost part of the arm.

5. A unit as claimed in Claim 3 or Claim 4, wherein the spindle is located inboard of a leading edge of the vane with respect to the intended direction of rotation of the arm such that at least a portion of vane between the spindle and the leading edge can contact part of the outer surface of the distribution arm when the vane is pivoted out of its rest position such that the distribution arm itself thereby forms the detent, 6. A unit as claimed in any of Claims 3 to 5, wherein the spindle is located on a leading side of a vertical plane passing through the longitudinal axis of the arm with respect to the intended direction of rotation of the arm.

7. A unit as claimed in any of Claims 1 to 6, wherein the vane is substantially rectangular in shape with its longer sides positioned parallel to the spindle.

8. A unit as claimed in any of Claims 1 to 7, comprising at least two distribution arms arranged in-line over the bed of the filter media and each provided with a wind vane arrangement.

9. A unit as claimed in any of Claims 1 to 7, comprising four distribution arms arranged in a cruciform arrangement and each provided with a wind vane arrangement.

10. A wind vane arrangement for a trickling filter unit as claimed in any of Claims 1 to 9, comprising a vane connected to a spindle that is pivotally mounted on at least one bracket adapted for connection to a distribution arm of the unit such that the vane can pivot about an axis substantially parallel to the longitudinal axis of the distribution arm.

ii. A trickling filter unit substantially as described herein with reference to any of the accompanying drawings.

12. A wind vane arrangement for a trickling filter unit substantially as described herein with reference to any of the accompanying drawings.