WO2002028504A1

WO2002028504A1 - Apparatus for cleaning the surface of a slow sand filter in a filterbasin of a water treatment plant

Info

Publication number: WO2002028504A1
Application number: PCT/SE2001/002184
Authority: WO
Inventors: Miodrag Jankovic; Miro JANKOVIC
Original assignee: Miodrag Jankovic
Priority date: 2000-10-06
Filing date: 2001-10-08
Publication date: 2002-04-11
Also published as: SE517199C2; SE0003618D0; SE0003618L; AU2001294468A1

Abstract

The invention relates to a bottom suction assembly for surface cleaning of the sand bed in a slow filter in a filter basin of a water treatment plant. The assembly is constituted by a float craft (1) which is movable in the basin and has an elongate suction nozzle (3) extending transversely across the float craft and being vertically adjustable to a predetermined depth in the sand bed and also including a sieve (5), arranged at its mouth, and a vibrator (6) mounted on the suction nozzle (3) in order to generate vibrations in the sieve (5) so as to separate algae an other contaminations which are at the same time sucked up through the nozzle by a pump (8), connected thereto, and are then transported to a filter bag (15) supported by the float craft (2).

Description

Apparatus for cleaning the surface of a slow sand filter in a filterbasin of a water treatment plant

The present invention relates to an apparatus for cleaning the surface of a slow sand filter in a filterbasin of a water treatment plant.

A slow-operating filter in a water treatment plant is the last filter of those through which the water passes before exiting from the water cleaning plant. Such a slowly functioning filter is in most cases constituted by a rectangular outdoor basin of varying size, comprising a sand bed with a height of about 1,5 m below a water layer also about 1.5 m deep. The filtration is achieved mechanically when water streams through the sand bed. The term surface cleaning refers to the work required for removal of an, a few centimeters thick, surface layer of the sand bed for cleaning purposes and for removal of the so called filter film which is formed automatically. This surface cleaning must be carried out with even time intervals the duration of which varies to match external circumstances, such as weather, location etc. This work is today performed with use of compact loaders, tractors and/or rear loaders. The first step of the surface cleaning is to empty out the water whereupon roughly 3 cm of the sand bed top surface layer is removed together with the filter film. The removed material is then transported to a sand drill. When, following the surface cleaning, the basin is refilled with water, the filter must, for a time period of at least 10 hours, be diverted to an adjacent selected lake before it can resume its normal operation. This procedure, involving drainage of the sand surface, causes disturbances in the microbacterial activity taking place in the sand bed. Each surface cleaning period lasts for about 1 month and is very work-requiring. The surface cleaning implies that about 6 cm of the sand bed is removed every year, meaning that the filters must be refilled with 10 years' interval.

Accordingly, the object of the present invention is to provide a bottom suction assembly of a new type intended for use to clean the surface of the sand bed in a slow-operating filter basin in a water treatment plant, and eliminating the problems mentioned above. The characterizing features of the invention are set out in the subsequent claims.

Thanks to the invention there has now been provided a bottom suction assembly for surface cleaning of the sand bed in a slow filter in a filter basin, which in an excellent manner performs its object and, in addition thereto, also is easy and cheap to manufacture. With the aid of a bottom suction assembly according to the invention a cleaning of the sand bed can be carried out without any need to empty out the water in the filter basin, an operation which per se has a most negative affect on the filter. Also, the assembly does only very little disturb the water production since, shortly after the surface cleaning, the slow- filter can again perform its ordinary operation. By use of an assembly according to the invention it becomes possible, by means of vibro energy and a sieve, to remove the upper surface layer of the sand bed down to a depth of a few centimeters, the sand being simultaneously washed and the filter film removed. Due to this washing of the sand, algae and other vegetables are disposed, after which a suction nozzle is used to suck up remaining residues for further transport up through a flexible tube to a filter bag in a float craft in the basin. The bottom suction assembly and the related suction nozzle can be moved above the filter basin, the suction nozzle being at the same time either pushed in front of the craft or pulled behind it. The suction nozzle, which is out elongate shape, can by means of a control device be vertically adjusted to a predetermined distance down into the sand bed. The contaminations which are separated from the sand during the washing by use of vibration energy in the water are sucked up at the same time as the cleaned sand is replaced in previous position.

A preferred embodiment of the invention is described below with reference to the drawings.

Fig.l is a diagrammatic, lateral, cross-sectional view of a suction nozzle for a bottom suction assembly according to the present invention,

Fig. 2 is a top view of a bottom suction assembly according to the invention, comprising a front-mounted suction nozzle, and

Fig. 3 is a top view of the sieve mounted on the suction nozzle shown in Fig. 1.

As appears from the drawings the bottom suction assembly 1, according to a preferred embodiment of the invention, is constituted by a float craft 2 displaceable in the basin and supporting a vertically adjustable suction nozzle 3. Attached thereto is a vibrator 4, adapted to vibrate the suction nozzle, and, mounted thereon, a sieve 5 which in a preferred, exemplifying embodiment is constituted by a fork, for the purpose of washing the upper layer of a sand bed 7 in a slow filter. The operational position of nozzle 3 is not dependent on the pump 8. The sieve 5, which is mounted on tghe suction nozzle 3, is arranged to sieve and wash the sand in the water 13 which is carried out in such a way that the algae and other vegetables get dispersed and, since the sand 12 is heavier, it will pass through the sieve 5. The sand 12 is separated and washed by the vibration energy transferred from the vibrator 6 to the sieve 5 and, after having been washed, the sand is replaced at the same location as before. The suction nozle 3 will then suck up the remaining algae and vegetables rests still in the sieve. A regulator is installed to adjust the working position of suction nozzle 3. The contaminations are, at a constant speed, transported through the pipes up to a filter bag 15 in the craft. This speed is stepwise increased along the passage route from the suction nozzle 3 to the pump 8.

The craft 2 is preferably driven by an electric motor 14 and the craft can either drag or push the suction nozzle and its related support arms behind or in front of itself, respectively.

In the example shown the width of the suction nozzle 2 is approximately 2000 mm. With the aid of the bottom suction nozzle according to the invention the sand can be washed and the remaining rests sucked up at a rate of about 17 m/min.

Claims

1. A bottom suction assembly for surface cleaning of the sand bed in a slowfilter in a filter basin in a water treatment plant, comprising a float craft (1) movable in said basin and having an elongate suction nozzle (3) extending transversally across the float craft, the nozzle being vertically adjustable to a predetermined operational depth in the sand bed, characterized in that the suction nozzle (3) at its orifice exhibits a sieve (5), a vibrator (6) being mounted on the suction nozzle (3) and arranged to generate vibrations in the sieve (5) in order to separate algae and other contaminations, which are at the same time sucked up with the aid of a pump (8) connected thereto and then transported to a filter bag (15) locataed on the float craft (2) , while the cleaned sand does by gravity sink back after the cleaning or washing procedure.

2. A bottom suction assembly according to claim 1, characterized in that the bottom suction assembly (1) comprises a regulator controlling the operational position of the suction nozzle (3) as related to the sand bed layer that is to be cleaned.

3. A bottom suction assembly according to claim 1, characterized in that the suction nozzle (3) has a width amounting to preferably about 2 m. and to which nozzle there are connected at least two flexible tube conduits (9-11) for transporting away the contaminations sucked up to the filter bag (15) of the float craft (2) .

4. A method for surface cleaning of the sand bed in a slowfilter in a filter basin in a water treatment plant by means of a suction nozzle and a pertaining sieve (5) , the nozzle being arranged to penetrate a predetermined distance down into the surface layer of the sand bed, the suction nozzle being simultaneously displaced across the sand bed, characterized in that the nozzle (3) and its related sieve (5) are caused to vibrate so that the algae and the contaminations which are separated from the sand bed are sucked up through the nozzle and transported on to a filter bag on the float craft, whereas the cleaned or washed sand does by gravity sink back after the washing.