CONTROL DEVICE FOR A UV-DISINFECTING SYSTEM WITH BROADBAND UV EMITTERS

Abstract

A device for monitoring and controlling water disinfecting systems having at least one broadband UV emitter arranged in a channel, wherein the device has at least one sensor, which is arranged in the water at a distance from the broadband UV emitter, and wherein the sensor is connected to a control unit, which is set up to control the output of the broadband UV emitter or the volumetric flow of water through the channel, wherein the sensor has a maximum sensitivity to UV radiation in a wavelength range between 200 nm and 240 nm.

Claims

1. A method for monitoring and controlling a water disinfecting system having at least one broadband UV emitter arranged in a channel, wherein at least one first UV sensor is provided, which is arranged in the water at a distance from the broadband UV emitter and wherein the first UV sensor is connected to a control unit, which is configured to control an output of the broadband UV emitter or of a volumetric flow of water through the channel, wherein: the first UV sensor has a maximum sensitivity between 200 nm and 240 nm, a signal of the first UV sensor is evaluated during operation, a UV dose in the wavelength range between 200 nm and 240 nm is calculated based on the signal from the first UV sensor, and the UV dose calculated at the site of the first UV sensor is used as a measurement for calculating a disinfection performance of the water disinfecting system.

2. The method according to claim 1, wherein a UV effectiveness spectrum of a predetermined microorganism is used to calculate disinfection performance.

3. The method according to claim 2, wherein the microorganism is selected from a group consisting of viruses, bacteria and protozoa for calculating disinfection performance.

4. The method according to claim 1, wherein a second UV sensor with a maximum sensitivity between 240 nm and 300 nm is provided and a measurement is calculated from a ratio of signals from the first UV sensor and the second UV sensor, which enables calculation of the dose taking account of a deterioration of the broadband UV emitter and a spectral absorption of the water.

5. The method according to claim 1, wherein an electrical efficiency of the broadband UV emitter is controlled according to the signal from the first UV sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] An embodiment of the present invention is described in detail below using the drawing. The drawing also shows the general technical background in the form of the UV spectra of various lamps and effect diagrams for the disinfection performance of various wavelengths on different microorganisms.

[0027] FIG. 1 shows a comparison between the spectrum of a low pressure lamp and the spectrum of a medium pressure lamp (prior art);

[0028] FIG. 2 shows the dependence of the effect of UV rays on different microorganisms on the wavelength (prior art);

[0029] FIG. 3 shows example transmission spectra for various types of fused silica;

[0030] FIG. 4 shows several absorption spectra of water samples in the range between 200 and 300 nm (Prior art from: USEPA (2006) Ultraviolet Disinfection Guidance Manual for the Long Term 2 Enhanced Surface Water Treatment Rule, EPA 815-R-06-007. Office of Water, Washington, D.C.);

[0031] FIG. 5 shows spectra of medium pressure lamps depending on the deterioration of the lamps;

[0032] FIG. 6 shows an arrangement as per the invention as a schematic block diagram; and FIG. 7 shows preferred sensitivity curves for the sensors in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

[0033] FIGS. 1, 2 and 4 show drawings from the prior art which are useful in terms of explaining the technical facts.

[0034] FIG. 1 shows two different spectra. The emission curve of a low pressure lamp is shown at 254 nm at the top in FIG. 1. It can be seen immediately that monitoring the UV emission at this wavelength is appropriate in order to control the overall UV radiation output of a low pressure lamp at a specific given value.

[0035] FIG. 1 shows at the bottom the spectrum of a medium pressure lamp. A large number of curves between 240 nm and approx. 370 nm can be seen here. Controlling the performance of such a medium pressure lamp solely on the basis of a UV sensor, which has maximum sensitivity at 260 nm, can only control the overall UV radiation output if the relative intensities of the various curves and the underlying continuum do not change.

[0036] It can be seen in practice, however, that firstly the proportion of UV radiation between 200 and 240 nm depends on design of the medium pressure lamp. Modern high-performance lamps emit a significant proportion of their overall radiation output in said shortwave range, whereas older lamps, which are designed and operated differently, only emit a small part of their overall radiation output in said range. FIG. 1 suggests in the lower spectrum that the overall proportion of the UV radiation of a medium pressure lamp in the range between 200 and 240 nm is low compared with the overall emission. However, in terms of biological effectiveness in water disinfecting systems, which are contaminated with microorganisms, it is precisely this wavelength range that is extremely significant. This can be demonstrated with the help of FIG. 2. FIG. 2 shows the effect of UV radiation on the DNA of various microorganisms depending on the wavelength. The different curves shown in FIG. 2 are scaled to a relative effect of 1 at 240 nm. It is noticeable that the effect of UV radiation between 240 and 300 nm on the microorganisms tested is more or less the same (with a fluctuation of perhaps approx. 50%). However, below 240 nm, the effect of the UV radiation on the DNA of the various microorganisms changes dramatically. There are microorganisms, which absorb relatively little UV radiation in the shortwave range and consequently the UV effect on these microorganisms remains relatively slight. However, there are other microorganisms, which show a considerable increase in UV absorption below 240 nm and thus also inactivation as a result of UV radiation.

[0037] FIG. 2 therefore shows that the variation in radiation output between 200 and 240 nm can, in the case of some microorganisms, make a huge difference in terms of the disinfection performance of a UV disinfecting system, if the effect of the UV radiation at low wavelengths increases as sharply as demonstrated in the case of some microorganisms in FIG. 2.

[0038] There are other influences on the spectrum of UV radiation which is emitted by a medium pressure lamp. The relationship between radiation output between 200 and 240 nm and the overall emission of the lamp is dependent only on the design and operating method of the lamp. If UV light spreads out from the radiation source, the light also interacts with the various materials in the radiation path before it reaches the microorganisms. The materials in the radiation path are firstly the gas filling of the lamp itself, the silica piston of the lamp, the air between the silica piston and a protective covering, a sheath that may be provided between the UV lamp and the water to be treated and finally the water itself. Absorption, reflection, diffraction and diffusion, which affect the spectrum, occur on these materials and their surfaces.

[0039] FIG. 3 shows, for example, the transmission spectra for UV radiation in various grades of fused silica. In the wavelength range of interest here between 200 and 300 nm, the synthetic fused silica identified as 021 has the best transmission of a sustained approx. 90%, whereas the fused silica identified as 219 shows a clear decrease below 260 nm and below 220 nm is virtually non-transparent to UV radiation. The grade identified as 124 has a minimum transmission at 245 nm and decreases again from 230 nm. At 200 nm, transmission is just 25%. FIG. 3 is intended to show that a medium pressure lamp, which emits a significant proportion of its radiation output between 200 and 240 nm, i.e. in the wavelength range which, according to FIG. 2 is particularly effective for some microorganisms, may lose its radiation output in this range either completely or partially in the event of an unsuitable selection of fused silica for the sheath. The range between 260 and 300 nm is virtually the same for the various silica grades. If the radiation output of the medium pressure lamp is controlled based on a sensor, which is only sensitive between 260 and 300 nm, absorption influences from various types of silica are not taken into account.

[0040] FIG. 4 shows various absorption spectra of water samples between 200 and 300 nm. Whereas water samples with very low UV absorption in the shortwave range only show absorption of approx. 20% at 200 nm, water samples with higher UV absorption are specified upwards of a wavelength range of approx. 230 nm with UV absorption of 40% or higher. Absorption at wavelengths of more than 240 nm is substantially the same for all samples. This example also shows that controlling radiation output using sensors, the sensitivity of which is between 260 and 300 nm, cannot take sufficient account of changes in the UV absorption of the treated water. If a UV sensor is used as per the invention to control and monitor the radiation output of the medium pressure lamp, which is sensitive in the range between 200 and 240 nm, the radiation reaching the site of the desired effect can be controlled reliably even if the UV absorption fluctuates.

[0041] FIG. 5 shows using examples how the spectra of medium pressure lamps change over an operating period of 3,266 hours. The higher emission spectra represent the output of new lamps whilst the curves below these reflect the output of aged lamps. It is clear that the deterioration causes output to be reduced by approx. 50% in the region of 260 nm, however the decline in output between 200 and 240 nm is significantly greater. In the bottom example, the range between 200 and 210 nm has ceased to exist almost completely.

[0042] When controlling the disinfecting system according to intensity in the region of 260 nm, it would therefore not be taken into account that the decline in output is significantly greater between 200 and 240 nm. It is therefore advantageous in terms of controlling a UV disinfecting system to control according to radiation output between 200 and 240 nm.

[0043] FIG. 6 shows a block diagram of a UV disinfecting system controlled as per the invention.

[0044] A channel 100 guides a flow of water (wastewater or drinking water). In the case of wastewater, the channel can be an open or a closed sluice. In the case of drinking water, typically a closed stainless steel channel is provided.

[0045] The water flows past a mercury medium pressure lamp 101, which is arranged in a UV transparent sheath 102 and consequently is not in contact with the water.

[0046] A first UV sensor 103 is arranged in the water at a distance from the sheath 102, said sensor is sensitive to UV radiation in the wavelength range between 200 and 240 nm. The distance between the first UV sensor 103 and the sheath 102 is selected such that there is a stretch of water between the first UV sensor 103 and the sheath 102, as said stretch of water is also in the middle between the sheath 102 and the microorganisms present in the water. The exact distance is not crucial, since it is more important that as much water lies between in the radiation path between the sheath 102 and the first UV sensor 103 such that a decrease in the UV radiation reaching the first UV sensor 103 can be measured during operation through the UV absorption of the water.

[0047] The first UV sensor 103 emits a signal during operation, which is representative of the incoming radiation intensity in the wavelength range between 200 and 240 nm. The signal is emitted via a first signal transmission 104 to a control unit 105. The control unit 105 in turn controls a power supply system 106 such that the lamp 101 produces the intended UV intensity which is necessary for the required disinfection performance.

[0048] The first UV sensor 103 is sensitive precisely in the range of the UV-C spectrum in which the disinfection effect depends very heavily on the biological effectiveness and the wavelength, particularly for different microorganisms. The first UV sensor 103 receives the radiation in the cited range emitted by the lamp 101, wherein a change in the output spectrum is taken into account in terms of time, absorption by the sheath and the water, dispersion and other influences. Output-reducing influences are taken into account which have less impact in the region of 260 nm wavelength.

[0049] Optionally, a further sensor can be provided as a second UV sensor 107, which is also provided for measuring the UV radiation in the water, which, however, as in conventional systems for monitoring or controlling broadband UV emitters, has its maximum sensitivity in the longer-wave range, at approx. 260 nm. Said second sensor 107 emits the radiation intensity in the longer-wave range of the UV-C spectrum to the control unit 105, which can then calculate from this the overall radiation output in the UV-C range and in the short-wave portion of the UV-B range, without however taking account of the particularly important short-wave UV-C range, which is covered by the first UV sensor 103. The control unit 105 can reach a conclusion on the condition of the disinfecting system and in particular the lamp 101 from the ratio of intensities, which are measured firstly by the first UV sensor 103 and secondly, by the second UV sensor 107, and can generate an alarm in the event of an excessive decrease in UV output in the wavelength range of the first UV sensor 103.

[0050] Lastly, FIG. 7 shows a sensitivity spectrum 203 of the first UV sensor 103 and a sensitivity spectrum 207 of the second UV sensor 107. The curve 203 for the first UV sensor 103 has maximum sensitivity at approx. 225 nm whereas there is virtually no sensitivity above 240 nm or below 200 nm. The curve 207 of the second UV sensor 107 has a maximum at 260 nm wherein the spectral sensitivity of the second UV sensor 107 is close to zero below 235 and above 295 nm.

[0051] The control system described thus allows precise monitoring and controlling of the disinfecting system in the important wavelength range between 200 nm and 240 nm and consequently precise information is available regarding the inactivation or disinfection performance to be achieved and also in respect of specific microorganisms where appropriate.