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| |  Posted 2/1/2008 11:51:06 AM | |
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| | All, During our dechlorination agent conversion from SO2 to Sodium Bisulfite,WET bioassay monitoring was conducted with a >50% mortality to the Mysid Shrimp. The lab feels it was due to a overdosing of the bisulfide because only the shrimp was effected which I agree. Anyway, does anyone have experience with the bisulfite dosing? IE enough for chlorine removal but not overdosing. Thanks, Phil |
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| | | Posted 2/1/2008 11:57:40 AM | |
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| | Phil, Using bisulfide for dechlorination is usually 1 part to 1 part. Excessive use of bisulfide will deplete oxygen and kill the test organisms.
Bob Whitworth |
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| | | Posted 2/1/2008 12:24:11 PM | |
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| | Thanks! I thought DO was monitored & controlled at a level of >4.0 mg/l during the 96hr test period. |
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| | | Posted 2/1/2008 1:43:00 PM | |
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| | Phil, You are most likely correct about maintaining the D.O. during the toxicity test procedure; it just came to mind about the D.O. depression.
Bob Whitworth |
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| | | Posted 2/5/2008 12:42:09 PM | |
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| | We use a feedback loop using an on line analyzer like http://analyticaltechnology.com/cms/Default.aspx?tabid=89 It is relatively cheap and uses diluted sulfuric acid as its only reagent. Be sure to install a system to bleach the sample lines automatically as bisulfite residual will grow slime that consumes both bisulfite and reacts with chlorine. Bisulfite does have a BOD, but chemical DO consumption requires a catalyst like cobalt. Old Std. Mthds. had an aerator test that depressed the DO by adding bisulfite and a cobalt catalyst. Measuring DO drop due to bisulfite on the lab bench showed a DO increase due to the DO probe stirrer. Adding a catalyst dropped the DO immediately. |
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