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| |  Posted 3/5/2007 2:14:07 PM | |
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| | The UV transmissivity design for disinfection for our activated sludge WWTP is 40%. The UV disinfection system has been on line for 1 year with no problems. Normal transmissivity is around 53%. Recently, the transmissivity began to decrease during one afternoon and by the next morning it was down to 7%. All other indicators appeared normal. This condition existed for 2 days and then gradually improved over the next 3 days until transmissivity returned to normal. Does anyone know of any type of industrial discharge that might have caused this? Types of industries discharging to the plant are specialty chemicals, electroplating, metal finishing, printed circuit board manufacturing, central waste treatment, industrial laundry, and groundwater remediation. |
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| | | Posted 3/6/2007 8:18:15 AM | |
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| There are lots of compounds that can affect the UVT. But here are some of the strongest UV absorbers:
Inorganic
Cobalt
Iron
Organic
Organic dyes
Humic acid
Although that doesn't answer your question, perhaps it may point you to the right direction. |
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| | | Posted 3/6/2007 9:50:02 AM | |
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| | I seem to remember, (but can't put my hands on the information) that printed circuit board manufacturing uses a masking agent in their plating processes that is a UV inhibitor. |
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| | | Posted 3/12/2007 11:26:11 AM | |
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| | Printed circuit board companies us a "UV resist" to coat the copper. They expose the resist to UV light through a mask so the UV light hardens the resist where they want the copper lines to be. Then they wash off the uncured resist and the copper leaving the copper traces where the UV resist was cured by UV light. Then they strip off the cured resist with another chemical. Needless to say the stuff absorbs UV. We had a factory that had effluent was crystal clear, but had to be diluted 1:100 to get a reading on the %UV transmittance meter. Take samples of your major trunk lines and test for %UVT. When you find the trunk with the low %UVT follow it up the trunk, checking at each sub trunk until you find the industry. Use their low %UVT as a dye to follow upstream. Chlorination of their effluent can destroy the double bonds that are absorbing the UV. You could require that they meet a %UVT on their discharge by chlorination or hyponation or switching to a different chemical process. The stuff will also have a high Cl2 demand if you were chlorinating. You can demonstrate the effect of Cl2 by dosing a sample in a beaker at different doses and measuring the %UVT. Is your plant upset? We found that the UV system would get hit if the plant was upset, normally it degraded the UV resist. You may have a different chemical causing the problem than we did. |
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| | | Posted 8/2/2007 11:16:48 PM | |
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| | Also check for dyes from textile industries. THey can be invisible (colorless) but absorb a lot of UV. Also measure suspended solids and colour in the effluent, when you measure UV%T, however for a 7 % UVT effluent these would be obvious. Grant |
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