GB2315259A

GB2315259A - Water sampling

Info

Publication number: GB2315259A
Application number: GB9614963A
Authority: GB
Inventors: Christopher Charles Whitworth
Original assignee: Yorkshire Water Services Ltd
Current assignee: Yorkshire Water Services Ltd
Priority date: 1996-07-12
Filing date: 1996-07-12
Publication date: 1998-01-28
Also published as: GB9614963D0

Abstract

There is disclosed a water sampling system for discontinuously extracting water from a sewer or similar body of water. The system is intermittently activated to pass a sample via water extracting lances 12,14 to a reservoir 42 by means of a pump 40. The water is passed through a cross flow filter 46 in the reservoir 42 to a feeder tank 58 from where it can be removed, possibly continuously, to be tested. The water extracting lances 12,14 comprise open ended tubes having horizontally disposed apertures (16, figure 2) which prevent the extraction of large particulate objects which might cause blockages. The open ends of the tubes face downstream with respect to the flow of water in the source so that matter does not enter the open ends of the lances, while matter which finds its way into the lances can escape. The cross flow filter 46 may be cooled or exposed to UV radiation or ultrasound to inhibit the growth of organisms thereon. Valves 30,32,34,36 can be set so that the pump passes a sample of water into the reservoir 42 or passes water in a loop from one lance to the other to effect back flow cleaning of the lance.

Description

WATER SAMPLING This invention relates to apparatuses and methods of water sampling.

Large scale, environmentally significant sources of water such as rivers, streams, sewers, water treatment plants and the like often require some form of monitoring, sometimes continuously. An important part of such a monitoring process is a suitable water sampling system. The system should be capable of delivering water at a desired flow rate and at an acceptable pressure, and should not be susceptible to blockage by matter present in the water. The latter point is particularly relevant to the sampling of sewer water, which, of course, contains a great deal of foreign matter.

Furthermore, the system should not require frequent downtime for removal of accumulated particulates or biological growth.

Prior art systems typically involve a suction intake that may utilise one or more "lances" positioned in the water source. A lance is a pipe or tube, straight or bent, with one or more apertures for water extraction or water return. Water is extracted continuously via the lance by suitable pumping means, and some proportion may then be abstracted and conditioned by a crossflow or other type of filter. The sample may then be returned via a similar lance, which has some benefits in terms of cleaning this lance for future use as a suction device. However, such systems are prone to build-ups of biological growth and particulate solids.

The present invention addresses the above mentioned problems and considerations.

According to a first aspect of the invention there is provided a water sampling system in which water is discontinuously extracted from a source during sampling.

The water may be extracted with a duty cycle of less than 50%.

The water may be extracted from a sewer, water treatment plant, river or the like.

The water sampling system may comprise at least one water extracting lance having a plurality of extraction apertures in which said apertures are disposed horizontally therein. The number of apertures may be greater than 100. The diameter of the apertures may be between 2 and 4mm.

The water sampling system may comprise at least two lances, and water may be flushed through the lances and returned to the source. This flushing may be continuous or performed at intervals.

The water sampling system may further comprise cross flow filtration means.

The cross flow filtration means may comprise an inclined mesh or a rotatable drum having a plurality of filtering apertures in the periphery thereof.

The cross flow filtration means may be cooled.

The cross flow filtration means may be exposed to UV radiation.

The cross flow filtration means may be exposed to ultrasound.

The filtered flow from the cross flow filtration means may be supplied to a feeder tank.

According to a second aspect of the invention there is provided a method of sampling water in which water is discontinuously extracted from a source during sampling.

The water may be extracted with a duty cycle of less than 50%.

Embodiments of the water sampling system according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a water sampling system; Figure 2 is a side view of components of a lance; and Figure 3a and 3b show an end view and a side view, respectively, of an embodiment of a cross flow filtration means.

Figure 1 is a schematic diagram of a water sampling system according to the present invention in which water is discontinuously extracted from a source 10 during sampling. It has been found that by extracting water discontinuously the build up of particulate matter, fibrous materials, rags and biological growth is inhibited.

The water is extracted with a duty cycle of less than 50%; extraction periods of between one and nine minutes followed by off periods oftwelve minutes have been employed, with a 3 minute/12 minute on/off cycle proving particularly advantageous.

In Figure 1 the water is extracted from a sewer; however, the system may be applied to the sampling of other water sources, such as water treatment plant, rivers and the like.

The water sampling system comprises two lances 12, 14 having a plurality of extraction apertures 16 in which said apertures 16 are disposed horizontally therein.

The lances are shown in more detail in Figure 2. For applications such as the sampling of sewer water it is important that these extraction apertures 16 are disposed horizontally: prior art lances have apertures located over substantially all of the lance circumference, a configuration that can lead to the pumping of air through apertures located on the top of the lance, and to the intake of grit and other particulate matter through apertures located on the bottom of the lance.

Preferably the number of apertures is greater than 100. In the embodiment shown in Figures 1 and 2 a total of 594 apertures, each of 3mm diameter, is employed, a configuration which has proved advantageous with the pumping system employed.

Whilst it is not possible to wholly prevent particulate matter entering the system, it is important that the dimensions of the apertures should not be too large so as to prevent the extraction of large particulate objects which might cause blockages. The lance comprises a main section 18, two extension sections 20 and threaded connecting sections 22, although clearly a one-piece configuration is also within the scope of the invention. Each section of the lance has three rows of thirty three apertures disposed horizontally on each side of the section. Each extension section 20 is 0.5m long; the horizontal length of the main section is also 0.5m.

It should be noted that the circular termini of the lances are open, but water is not sampled via this (large) aperture because the lances face downstream, and the sample velocity is too low. These end aperture are useful because they provide an exit route for large or odd shaped solids during draindown periods.

The lances 12, 14 are connected via flexible hoses 24, 26 to a manifold 28 comprising manual valves 30, 32, 34, 36, an automated valve 38 and a pump 40 of 251mien~ pumping capacity, connected in-the manner shown in Figure 1 by appropriate tubing. During water extraction phases the valves 30, 32 are opened, whilst valves 34, 36 and automated valve 38 are closed. Automated valve 38 opens when the pump 40 is off. It has been found that it is advantageous to flush the system approximately once a month by, for instance, closing valve 32, and opening valve 36 thus extracting water through lance 12 and returning same through lance 14.

Water thus extracted flows into cross flow filtration means 42 from a inflow pipe 44. A preferred, but non-limiting, embodiment shown in Figures 1 and 3 comprises an inclined 30 )lm mesh 46. By inclining the mesh 46, the incoming water flows over substantially all of the mesh surface. The provision of a flow spreader 48 results in the formation of a weir 50, which enhances the flow of water over the mesh surface. The washing action provided by the flow of water over the mesh 46, together with the fact that substantially all of the mesh 46 is used, reduces the frequency with which the mesh is cleaned, an operation resulting in system downtime. Water overflowing the mesh 46 flows to a drain via a waste flow pipe 52. Filtered water collects in a filtrate collection vessel 54 located beneath the mesh 46, and flows via a feed pipe 56 into a feeder tank 58.

It should noted that "cross flow filtration means" is defined in a fairly loose sense : a new mesh 46 has a throughput of 10 lmin-1, dropping to 2 lmin~' within a few days. Cleaning of the mesh 46 is required after about one week of operation; cleaning may be effected with a high pressure washer. Biological growth on the mesh 46 is a major cause of blockage : it may provide desirable to cool the mesh and/or expose the mesh to UV radiation and/or expose the mesh to ultrasound in order to inhibit such growth.

Other cross flow filtration means are also within the scope of the invention.

One possibility would be a commercial available rotatable drum type filter having a plurality of filtering apertures on the periphery thereof.

From the feeder tank 58 water flows continuously via pipe 60 having a vertical drop of 1.5m to the desired application. Flow rates of 200 mlmin' are achieved at negligible water pressure.

The feeder tank 58 has a drain pipe 62 fitted with an automated valve 64.

The operation sequence is as follows The pump starts and automated valve 38 closes, whilst automated valve 64 opens for 60 seconds and then closes. The pump stops after 3 minutes - or earlier if a level indicator on the feeder tank 58 indicates that the tank is full - and automated valve 38 opens. The pumps remains off for 12 minutes.

In this manner water is sampled continuously even though the initial water extraction step is not continuous. By extracting water intermittently the system becomes blocked less readily and has to be cleaned less frequently than continuous extraction systems.

Claims

1. A water sampling system in which water is discontinuously extracted from a source during sampling.

2. A water sampling system according to claim 1 in which the water is extracted with a duty cycle of less than 50%

3. A water sampling system according to claim 1 or claim 2 in which the water is extracted from a sewer, water treatment plant, river or the like.

4. A water sampling system according to any of the previous claims comprising at least one water extracting lance having a plurality of extraction apertures in which said apertures are disposed horizontally therein.

5. A water sampling system according to claim 4 in which the number of apertures is greater than 100.

6. A water sampling system according to claim 5 in which the diameter of the apertures is between 2 and 4mm.

7. A water sampling system according to any of claims 4 to 6 comprising at least two lances in which water may be flushed through the lances and returned to the source.

8. A water sampling system according to any of the previous claims further comprising cross flow filtration means.

9. A water sampling system according to claim 8 in which the cross flow filtration means comprises an inclined mesh.

10. A water sampling system according to claim 8 in which the cross flow filtration means comprises a rotatable drum having a plurality of filtering apertures in the periphery thereof.

11. A water sampling system according to any of claims 8 to 10 in which the cross flow filtration means is cooled.

12. A water sampling system according to any of claims 8 to 11 in which the cross filtration means is exposed to W radiation.

13. A water sampling system according to any of claims 8 to 12 in which the cross filtration means is exposed to ultrasound.

14. A water sampling system according to any of claims 8 to 13 in which the filtered flow from the cross flow filtration means is supplied to a feeder tank.

A A method of sampling water in which water is discontinuously extracted from a source during sampling.

16. A method according to claim 15 in which the water is extracted with a duty cycle of less than 50%.

17. A method according to claim 15 or claim 16 in which the water is extracted from a sewer, water treatment plant, river or the like.