AWWA WKICO66059

This powerpoint presentation looks at a problem that the Massachusetts Water Resources Authority (MWRA) had with how hits for cyanide in ozone-treated water samples. MWRA set up a study on whether cyanide was really in the samples, or was it forming in the sample container during preservation and storage. A literature search found that there is growing evidence, especially on the wastewater side, that cyanide can form in the bottle. The hypothesis as stated in the presentation was that preservation interrupts a series of chemical reactions between formaldehyde, an ozone disinfection byproduct (DBP), and chlorine/chloramines that normally convert formaldehyde into CN- to cyanogen chloride (CNCl), and on to non-toxic cyanate (CNO-). A bench-scale experiment and results are presented, that showed: unspiked and spiked samples formed detectable cyanide over 2 to 10 days of storage; this happened with both Thiosulfate and Ascorbic acid dechlorination; and, Thiosulfate had twice as many hits, and higher concentration hits, than Ascorbic Acid. The on-site experiment is presented, using a Micro Dist Tube, with results indicating that only the samples handled in the conventional way had detectable amounts of cyanide. Conclusion from these studies: cyanide can form in preserved drinking water samples; formaldehyde appears to stimulate cyanide formation; and, stabilizing samples in MICRO DIST tubes on-site, without raising to pH 12 appears to avoid cyanide formation. Includes figures.