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Bromamine decomposition and cyanogen bromide formation in drinking water from monobromamine and formaldehyde

Posted on:2004-08-07Degree:Ph.DType:Dissertation
University:University of Illinois at Urbana-ChampaignCandidate:Lei, HongxiaFull Text:PDF
GTID:1461390011966469Subject:Engineering
Abstract/Summary:
When monochloramine is applied to drinking water as a disinfectant, it can react with bromide ion, a common species present in natural waters, to form bromamines. Hypobromous acid, formed through oxidation reactions, reacting with ammonia is another way to introduce bromamines into drinking water. The formation of bromamines helps decrease bromate formation by decreasing the available free bromine, which is necessary for bromate formation pathways. Even though bromamines are important for disinfection byproducts (DPBs) formation, the chemistry of bromamines and their roles in DPBs formation are far from well understood. For this reason, bromamine decomposition kinetics was investigated over a pH range of 6.7 to 9.5, which is usually encountered in drinking water treatment.; Even though under typical drinking water conditions, dibrommaine (NHBr 2) is the dominant species, monobromamine (NH2Br) is the product formed first from HOBr reacting with ammonia. NHBr2 is then formed through the disproportionation reaction of NH2Br: 2 NH2Br↔NHBr 2 + NH3, which undergoes general acid catalysis. The decrease of total bromamines occurs via the following two decomposition reactions: 2 NHBr2→products; NH2Br + NHBr2→products. These two reactions are both assisted by basic species, such as HPO4 2− for the first reaction, and OH− and CO32− for the second reaction, as observed under the experimental conditions investigated.; The establishment of a bromamine decomposition model makes it possible to study the formation of BrCN from formaldehyde (HCHO) and NH2Br, which occurs at similar rate to bromamine decomposition. NH2Br in this scheme depletes through two pathways: one by the disproportionation reaction of NH2Br, the other by reacting with HCHO. The reaction mechanisms are:; HCHO + NH2 Br ↔ CH2(OH) NHBr CH2(OH)NHBr → CH2NBr + H2O CH2NBr → HBr + HCN CN− + NH 2Br + H+ → BrCN + NH3 CN− + NHBr 2 + H2O → NH2Br + BrCN + OH− ; The last two reactions can be singled out and studied independent of the other reactions including bromamine decompositions because the reactions are extremely fast. The BrCN producing reaction from NH2Br is mediated in general by the acids: H+, H2PO4 −, HPO42−, H...
Keywords/Search Tags:Drinkingwater, Bromaminedecomposition, Cellrulerty, Formation, Reaction
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