AU657192B2 - Improvements in pollution monitoring - Google Patents

Description

657192 p00011 Regulation 3.2

AUSTRALIA

Patents Act, 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Original TO BE COMPLETED BY THE APPLICANT NAME OF APPLICANT: *O MEASURING CONTROL EQUIPMENT CO.

PTY. LIMITED (ACN 004 740 863) LAWRENCE A. CAMPBELL ACTUAL INVENTOR: 8t***I ADDRESS FOR SERVICE: 00 Peter Maxwell Associates Blaxland House, Suite 10, 5 Ross Street, NORTH PARRAMATTA NSW 2151 IMPROVEMENTS IN POLLUTION

MONITORING

INVENTION TITLE: DETAILS OF ASSOCIATED PROVISIONAL APPLICATION NO: PL 0522 22ND JANUARY, 1992 The following statement is a full description of this invention, including the best method of performing it know to me:- -2- The present invention relates to improvements in pollution monitoring and, in particular, to a measurement apparatus for detecting or measuring physical and chemical properties of wastewater. In this specification, the term wastewater encompasses all forms of liquid effluent and sewage.

The measurement of pollution level indicators in wastewater with the aid of permanently installed sensitive measurement devices such as electrodes, probes and transducers has often led to unreliable results in view of the contamination of the measurement devices with the waste.

•Unless adequate cleaning of the measurement devices is undertaken, the long periods of time in which most o: these measurement devices are expected to work without service, a a during which time they are immersed in the wastewater, will lead to severe contamination and poisoning of the device.

This is usually caused either by surface oil and debris forming a coating on the sensing part of the device or as a o result of the long term effect of harsh chemicals reacting 0* with the device.

a S, "For example, pH probes will not maintain stability when subjected to the high sulphide levels normally present in sewer wastewater. Dissolved oxygen probes also suffer severe degradation and many electro-chemical electrodes will not retain long term stability due to chemical poisoning.

The regular cleaning of such permanently installed measurement devices to slow the rate of contamination has, however, not always been possible because of difficulties -3associated with removing the devices from their immersed environment.

For example, when a probe is raised from the wastewater, the probe may often by coated by surface oil and debris contained in the wastewater and these contaminants may not always be readily washed off the probe during the washing cycle, thereby adversely affecting the probe reading upon subsequent reimmersion.

It is an object of the present invention to overcome or substantially ameliorate the disadvantages of the prior art.

According to the invention there is provided a measurement apparatus for detecting or measuring a desired physical or chemical property of wastewater, the apparatus adapted to be at least partly immersed in the wastewater, the apparatus comprising:an immersible enclosure, the enclosure having an opening for receiving wastewater therewithin, a measurement device located within and immersible with

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.he enclosure, the measurement device being adapted to detect or measure a desired physical or chemical property of the wastewater, gas transfer means adapted to supply gas to or vent gas from the enclosure, liquid spray supply means adapted to supply liquid spray onto the measurement device, and control means for co-ordinating the supply of gas and liquid spray into the enclosure when the apparatus is being -4at least partly immersed, so that wastewater does not enter the enclosure and so that any contaminants at the wastewater/gas interface at the enclosure opening are removed, (ii) terminating the supply of gas and liquid spray after a predetermined period and venting gas from the enclosure to atmosphere so that the wastewater level rises in the enclosure and at least partially immerses the measurement device.

Preferably, the control means also co-ordinates the supply of gas and liquid spray into the enclosure after the measurement is made, so that wastewater is removed from the 9* enclosure through the opening and so that any wastewater and any contaminants thereof are washed off the measurement device.

Preferably, the gas transfer means includes a valve controlling both the supply of gas under pressure to the enclosure and the venting of gas to atmospheric from the 9 enclosure.

Preferably, the liquid spray supply means includes a valve which controls the supply of liquid spray onto the 0* measurement device.

Preferably, the liquid spray supply means also includes a plurality of spray nozzles disposed within the enclosure and directing liquid spray onto the measurement device.

Preferably, the opening of the enclosure is at the underside thereof.

Preferably, the control means terminates the supply of C. S

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gas and liquid spray after a period that allows sufficient removal of contaminants from the wastewater/gas interface so that a reliable measurement of the desired physical or chemical property of the wastewater may be made.

In another embodiment of the invention, the measurement apparatus includes a plurality of measurement devices, each device adapted to detect or measure a different desired physical or chemical property of the wastewater.

In use, the measuring apparatus of the invention may be partly or fully immersed in the wastewater.

According to another aspect of the invention, there is provided a method for detecting or measuring a desired physical or chemical property of wastewater, the said method using the aforementioned measurement apparatus and comprising 15 the steps of:at least partly immersing the enclosure of the apparatus in the wastewater and simultaneously co-ordinating the supply of gas and liquid spray into the enclosure during immersion so that 20 wastewater does not enter the enclosure and so that any contaminants floating on the wastewater/gas interface at the enclosure opening are removed, (ii) separately terminating the supply of gas and liquid spray after predetermined periods representative of substantial removal of said contaminants and so as to allow the wastewater to reach an equilibrium state, and -6- (iii) venting gas from the enclosure to atmosphere so that the wastewater level rises in the enclosure and at least partially immerses the measurement device, whereby a reliable measurement of the desired physical or chemical property of the wastewater may be made.

In order that the invention may be more readily understood and put into practical effect, reference will be made to the accompanying drawings, in which:- Fig. 1 is a side view of a measurement apparatus of the prior art immersed in wastewater with the probe surface contaminated with an oily coating *o acquired from the surface of the wastewater, Fig. 2 is a side view of the contaminated probe and apparatus of Fig. 1 having been removed from the wastewater and being washed by water spray jets, Fig. 3 is a sectional side view of a measurement apparatus according to a preferred embodiment of 0 the present invention, including a probe thereof, about to be immersed in wastewater, Fig. 4 is a sectional side view of the measurement apparatus of Fig. 3 immersed in wastewater and showing a first stage of preparing the probe for the measurement, Fig. 5 is a sectional side view of the measurement apparatus of Fig. 4 in a second stage where the desired measurement can be made, and, Fig. 6 is a sectional side view of the measurement -7apparatus of Fig. 5 in a third stage where the measurement has been made and the probe is being cleaned.

The measurement apparatus 10 of the prior art shown in Figs. 1 and 2 has a probe 11 for measuring a desired chemical or physical property of the wastewater 12 in which the probe 11 is immersed, such as the pH or dissolved oxygen concentration, via an electrical connection 13 to a measurement recorder (not shown).

The probe 11 is shown in Fig. 1 coated with a contaminating layer 14 of surface oil and debris derived from the wastewater 12. The contaminating layer 14 will interfere with the reading of the probe 11 and an erroneous measurement o of the desired property of the wastewater will be recorded.

Washing the probe 11 with water spray jets 15, as shown in Fig. 2, is unlikely to remove completely the contaminating oil and debris layer 14 and so, when the probe 11 is reimmersed in the wastewater 12 for a further measurement, an erroneous measurement will again result that is likaly to be more pronounced in error than the earlier measurement.

The measurement apparatus 20 of Fig. 3 to 6 also has a probe 21 for measuring a desired chemical or physical property of the wastewater 22 in which the probe 21 will be immersed. The probe 21 has an electrical connection 23 to a measurement recorder (not shown).

The probe 21 may alternatively be an electrode or transducer or a like measurement device or plurality of devices.

The probe 21 is surrounded by and mounted in an enclosure or shroud 24 having an opening 25 at its underside.

The shroud 24 serves as a 'diving bell' type enclosure as it is immersible in the wastewater.

The shroud 24 is connected to air transfer means consisting of an air supply chamber (not shown) supplying air under pressure via an air transfer valve 26 to an air transfer tube 27 having an opening 28 to the interior 29 of the shroud 24. The valve 26 can be set so that supply of pressurized air from the air supply chamber to the air '."transfer tube 27 is blocked and air is free to pass from the air transfer tube 27 (and hence from the interior 29 of the shroud 24) to the atmosphere under atmospheric pressure via a air valve outlet 32. In this way, the air transfer means can supply air to or vent air from the shroud 24.

,e The shroud 24 is also connected to liquid spray supply means consisting of a liquid supply chamber (not shown) supplying liquid under pressure via a liquid supply valve (not shown) to a liquid supply tube 30 having a plurality of liquid spray nozzles 31 opening to the interior 29 of the shroud 24. When the liquid supply valve is open, the nozzles 31 can direct pressurized liquid in the form of a spray onto the probe 21 for washing the probe 21.

The liquid used for the spray may be clean water, but may be a buffered aqueous solution as in the case when a pH electrode requires washing and recalibration, or a detergent solution.

Fig. 4 shows the first stage in preparing the probe 21 for its measurement. The apparatus 20 may either be lowered into the wastewater 22 or the wastewater 22 may be allowed to rise to a level where the lower portion of the shroud 24 is immersed in wastewater. However, wastewater is restricted from entering through the opening 25 to the interior 29 of the shroud 24 by opening the air transfer valve 26 and liquid supply valve to supply air and liquid under pressure to the shroud interior 29. The air transfer valve 26 is, of course, set so that air cannot escape from the shroud interi..or 29 through the valve outlet 32 to the atmosphere during immersion of the apparatus The pressurized air and liquid supplied to the shroud 0 interior 29 serve a number of purposes. The pressurized air 06 prevents the surface of the wastewater 22 from entering the interior 29 through the opening 25 by providing a positive air pressure in the interior 29, thereby preventing any 9 wastewater 22 contacting the surface of the probe 21. The pressurized liquid spray removes any residual contamination 0 from the surface of the probe 21 but, more importantly at this stage, serves to break up any film of surface oil 5 floating at the wastewater/air interface at the shroud opening 25. The pressurized air, by bubbling out through the opening 25, also serves to break up any oily film and causes the smaller conglomerations of oil and any debris to be moved away from the wastewater/air interface at the shroud opening to the wastewater surface surrounding the shroud 24 where the oil and debris cannot contaminate or interfere with the reading of the probe 21.

In a second stage as shown in Fig. 5, where the desired measurement can be made, the supply of pressurized liquid is terminated for a time sufficient to allow untainted wastewater 22 to surround the shroud 24. The supply of pressurized air is then terminated to allow the wastewater/air interface at the shroud opening 25 to stabilize. Once an equilibrium state representative of the physical and chemical properties of the wastewater surrounding the shroud 24 has been reached, the air from the shroud interior 29 is vented to atmosphere by adjustment of air transfer valve 26 to allow air flow communication between 0 the air transfer tube 27 and the air valve outlet 32. The level of the untainted wastewater/air interface will, as a

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result, rise through the shroud interior 29 as pressurized air is vented to at 'osphere until the wastewater level in the shroud interior 29 corresponds to the level of the wastewater o. surrounding the shroud 24. Alternatively, pressurized air may be released controllably so that a lower level of ft pressurized air remains in the shroud interior and the wastewater/air interface is at a suitable level.

•Although the use of the measurement apparatus of the invention has, in relation to Fig. 5, been described as involving partial immersion of the enclosure 24, it is to be understood that the enclosure 24 could be fully immersed in the wastewater. In the case of full immersion, appropriate arrangements would need to be made to exhaust the enclosure or shroud 24 of the washing liqaid and pressurised air.

At the desired inte-face level, the probe 21 should be -11suffiiently immersed in wastewater 22 so that reliable readings of the desired physical or chemical properties of the wastewater can be made free of any contaminating oil or debris that might interfere with the readings or damage or otherwise compromise the functional integrity of the probe.

It is important that, in the course of removing the contaminants, such as oil and debris, from the wastewater/air interface, the desired physical or chemical properties of the wastewater to be sampled by the probe 21 in the shroud interior and which are sought to be measured are not affected.

After the measurement of the probe 21 has been made, Fig. 6 shows a third stage where the probe 21 is being washed

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or cleaned. The apparatus 20 ne.ed not be raised from the wastewater during the washing stage.

Pressurized air is again supplied into the shroud s interior 29 by adjustment of the air transfer valve 26 to the configuration as shown in Fig. 6. The introduced pressurized air lowers the level of the wastewater/air interface unt... it is below the probe 21 and preferably at a level corresponding to the shroud opening The washing of the probe 21 with pressurized liquid spray supplied through the liquid supply tube 30 and directed through the nozzles 31 can then begin. The supply of pressurized air is maintained during the washing of the probe 21 and assists the flow of liquid in the washing process whilst maintaining the wastewater/air interface below the probe 21.

-12- After the probe washing has been dleted, by stopping the supply of liquid, the apparatus 20 can be left immersed in the wastewater 22 as long as there is sufficient pressurized air continuously or periodically fed into the shroud interior 29 to maintain the wastewater/air interface at a level below the probe 21. In this way, the shroud 24 will act as a kind of 'diving bell' and the pressurized air therewithin will ensure that the probe 21 remains uncontaminated by oil and debris from the wastewater and any gaseous contaminants while immersed therewithin for long periods of time.

Periodic or continuous washing of the probe 21 between 0*00 00 measurements can also lead to prolonged functional life and

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reduced likelihood of contamination of the probe 21.

The measurement apparatus of the invention has numerous other advantages. For instance, by monitoring the pH level t of a buffered washing liquid in the liquid supply chamber and comparing it with the pH measured by the probe while being

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00.0. washed, it is possible to detect significant levels of drift in the pH probe. This technique can be further extended to 000005 spraying the probe with buffer solutions to both calibrate and clean the probe. The pH level of the buffered liquid may be monitored by a separate probe located in the liquid supply chamber.

In-situ calibration of dissolved oxygen probes is possible. This can be achieved by taking the dissolved oxygen measurement during or just after the liquid washing cycle while air flow into the shroud is still maintained to -13ensure a 100% dissolved oxygen saturation level.

The measurement apparatus of the present invention may also be adapted to include a plurality of measurement devices located within and immersible with the enclosure or shroud, so that measurements of any number of physical or chemical properties of wastewater can be made, either simultaneously or at different times.

Alternatively, a single measurement device may be used that is able to measure more than one physical or chemical property of the wastewater.

In some circumstances such as with certain probes (for example, dissolved oxygen probes) it may be desirable to interrupt the flow of the liquid washing solution and replace 0* it with a flow of air so that the accuracy of the probe output may be checked during the time the washing cycle is replaced by flow of air.

Various other modifications may be made in details of design and construction without departing from the scope or 0 ambit of the invention.

Claims (13)

1. A measurement apparatus for detecting or measuring a desired physical or chemical property of wastewater, the apparatus adapted to be at least partly immersed in the wastewater, the apparatus comprising:- an immersible enclosure, the enclosure having an opening for receiving wastewater therewithin, a measurement device located within and immersible with the enclosure, the measurement device being adapted to detect or measure a desired physical or chemical property of the "wastewater, o'oo* gas transfer means adapted to supply gas to or vent gas from the enclosure, 4 liquid spray supply means adapted to supply liquid spray onto the measurement device, and control means for co-ordinating the supply of gas and liquid spray into the enclosure when the apparatus is being 4 at least partly immersed, so that wastewater does not enter the enclosure and so that any contaminants at the wastewater/gas interface at the enclosure opening are removed, (ii) separately terminating the supply of gas and liquid spray after predetermined periods and venting gas from the enclosure to atmosphere so that the wastewater level rises in the enclosure and at least partially immerses the measurement device.

2. The measurement apparatus of claim 1 wherein the control means also co-ordino.tes the supply of gas and liquid spray into the enclosure after the measurement is made, so that wastewater is removed from the enclosure through the opening and so that any wastewater and any contaminants thereof are washed off the measurement device.

3. The measurement apparatus of claim 1 or claim 2 wherein the gas transfer means includes a valve controlling both the supply of gas under pressure to the enclosure and the venting of gas to atmosphere from the enclosure.

4. The measurement apparatus of any one of claims 1 to 3 wherein the liquid spray supply means includes a valve which controls the supply of liquid spray onto the measurement device.

The measurement apparatus of claim 4 wherein the liquid spray supply means also includes a plurality of spray nozzles disposed within the enclosure and directing liquid spray onto the measurement device. ooo*@

6. The measurement apparatus of any one of claims 1 to wherein the opening of the enclosure is at the underside thereof. 0*

7. The measurement apparatus of any one of claims 1 to 6 wherein the corLtrol means separately terminates the supply of gas and liquid spray after periods that allow sufficient removal of contaminants from the wastewater/gas interface so that a reliable measurement of the desired physical or chemical property of the wastewater may be made.

8. The measurement apparatus of any one of claims 1 to 7 -16- wherein the gas is air.

9. The measurement apparatus of any one of claims 1 to 8 wherein the liquid is water.

The measurement apparatus of any one of claims 1 to 9 including a plurality of measurement devices, each device adapted to detect or measure a different desired physical or chemical property of the wastewater.

11. The measurement apparatus of any one of the preceding claims wherein the control means is adapted to interrupt the flow of liquid for a predetermined period to permit testing of the probe in the presence of air.

12. A method for detecting or measuring a desired physical 99 or chemical property of wastewater, the said method using the 9 measurement apparatus of any one of claims 1 to 10, and comprising the steps of:- at least partly immersing the enclosure of the 9 apparatus in the wastewater and simultaneously co-ordinating the supply of gas and liquid spray into the enclosure during immersion so that wastewater does not enter the enclosure and so eo0ae "that any contaminants at the wastewater/gas interface at the enclosure opening are removed, (ii) separately terminating the supply of gas and liquid spray after predetermined periods that allow sufficient removal of said contaminants and so as to allow the wastewater to reach an equilibrium state, and -17- (iii) venting gas from the enclosure to atmosphere so that the wastewater level rises in the enclosure and at least partially immerses the or each measurement device, whereby a reliable measurement of the desired physical or chemical property of the wastewater may be made.

13. A measurement apparatus substantially as hereinbefore described with reference to any one of Figs. 3 to 6. Dated this 20th day of January, 1993. 0 MEASURING AND CONTROL EQUIPMENT PTY. LIMITED S Patent Attorneys for the Applicant: PETER MAXWELL ASSOCIATES S 93 1 93 1 003 S .5.5 ABSTRACT A partly immersible measurement apparatus (20) for detecting or measuring a desired physical or chemical property of wastewater, such as pH or oxygen concentration, has an enclosure (24) with an opening (25) thereto at its underside. The enclosure (24) contains a measurement device such as a probe, mounted therewithin, as well as gas transfer means (26, 27, 28, 32) for supplying gas to or venting gas from the enclosure and liquid spray supply means (30,31) for supplying liquid spray onto the measurement device The apparatus (20) includes control means for, in sequence, preparing the measurement device (21) for °0°00 measurement, taking the measurement, and washing the *4 measurement device (21) after the measurement has been taken. 0 0 see@ *0 *54o* 44