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| |  Posted 8/25/2006 2:48:43 AM | |
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| | For a wastewater client in the middle east we are looking at closed versus open UV disinfection system. due to site constraints it appears that closed system (with medium pr. lamps) would be appropriate over the open system using low pr. lamps and would serve the purpose. Can someone put some light on which system to use - You can get varied and opposite responses depending which manufacturer representative you happen to discusses this with. Any help in this regard would be greatly appreciated. Thanks in advance. regards, Tatya. |
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| | | Posted 8/30/2006 10:59:11 AM | |
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Supreme Being
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| | I like the closed medium pressure systems because you vary the power by shutting off individual lamps. The lamps are perpendicular to flow. Most open channel lamps are parallel to flow so all the lamps in a bank need to be on (and aging) to avoid a path with low UV energy. The ballasts must be more complicated to allow dimming like some of the medium pressure in channel units or you have to bring on an entire module to increase the dose. There are vertical low pressure open channel models that can turn on and off individual rows of lamps as the flow or transmittance changes. The most important thing is to measure %UV transmittance before design. Some industrial discharges may look crystal clear, but in the UV spectra, they are opaque. Don't base the design on a single grab, buy an analyzer and measure at least several months of composites and at least as couple of individual 24 hour discrete sample to insure no surprises. Test each industries discharge too. |
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| | | Posted 4/30/2007 3:34:43 PM | |
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| | Rob, Our plant is also looking at installing a UV system. I am currently starting to perform the UV Scans on the plant effluent. My question for you, is what range to you recommend that you scan the effluent and other samples with? (220 nm to 400nm??) My other question for you is that when a scan for % Transmittance, I notice that there appears to be a difference of how the instrument is zeroed. I have run my scans both ways, zeroed against air and zeroed against distilled water. What is the proper method for running the % transmittance based on what the engineers design against?? Thanks, Patti |
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| | | Posted 5/1/2007 10:55:26 AM | |
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Supreme Being
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| | There are several %UVT analyzers on the market, all the UV equipment manufactures sell them. We used one of their dedicated analyzers that just measure at 253.7 one centimeter path length. You zero with DI water that has an organic removal cartridge. Below is one meter I found on the web. There are also online meters available. You may be able to borrow a meter from a potential UV vendor. http://www.metexcorporation.com/HF_Scientific/micro_uvt-15_photometer.htm |
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| | | Posted 8/2/2007 11:10:43 PM | |
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| | One issue you need to firstly clarify is whether the system needs to be validated (eg NWRI standard). For wastewater applications the NWRI valiadation is usually carried out on open channel sysytems at wastewater UV%Ts. Closed systems are usually validated on potable water UVTs. Alternatively you can carry out your own site validation. The big advantage is that higher UV power inputs can be achieved with the MP closed units. This makes the unit more compact. Other issues between open and closed systems is the type of lamp. Closed systems are usually MP lamps. There are a few exceptions. MP lamps are less electrically efficient (greenhouse gas) and lamp life approximately half. Thus operating costs are higher. Closed systems often are lower in capital cost. Selection of a system needs also to look at hydraulics. If you need to construct an open channel system metres up in the air then it may be more cost effective to pipe the system through a closed pipe system at ground level. Another issue is that MP systems are often designed as a single lamp. These systems are better suited to high UV%T effluent, because there is a large variation in delivered dose, for different parcels of fluid that pass through the reactor. This issue led to the development of the USEPA UV Disinfection Design Manual, and derating of dose. Regards UV%T measurements, I recommend that you carry out a sampling scheme over say a year. UV%T is affected by: Suspended solids (sample after PDWF and during PWWF), Colour (potable water colour due to seasonal supplies, trade wastes such as wool scour, dyeing, yeast, abbatoir blood, colour, etc.) and effectiveness of the activated sludge system (adequacy of oxygen input). Dose is also affected by SS and sludge age. Regards Grant H |
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