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Water-poor coastal regions of the world are turning increasingly to desalinationof seawater for supply. Tampa, Florida has a plant under construction andSan Diego, CA is considering one. In addition, the State of Texas isevaluating a large-scale desalination demonstration project for several sitesalong its Gulf Coast. While much of this desalination relies on membraneprocess sites where electrical power is generated using steam are uniquelysuited to distillation processes.The Water and Power Authority of the USVI (WAPA) has operatedhypobaric distillation desalination plants on the three major islands for over10 years. The two major plants each provide potable water for populationsof about 50,000 persons. In the last two years one of the islands experienceda sudden increase in TTHMs at the long-residence-time site (LRT). Thisincrease was roughly concomitant with changes in passivation for corrosioncontrol in the distribution system and a number of other changes, includingseveral in disinfection practices. Unlike most THMs in most systems, thosein the WAPA system were between 50% and 70% bromoform, with up to90% brominated species.Efforts of the Authority to address the problem are reviewed in this paper and the possiblecontribution of electrolytic generation of mixed-oxidant disinfectantsis discussed, along with a review of the possibility of passivation chemicaladdition contributing to the problem. A factor most likely to affect isolatedsystems subject to severe interruptions in production, such as canresult from hurricane damage, is the large amount of finished water storagerequired against such interruptions.It was found that several factors contributed to the problem, includingautomatic disinfectant rate control, operation of storage facilities, instantaneouswater supply demand changes and possibly application of mixedoxidantsgenerated on-site. For each contributing factor the corrective actionstaken by the Authority and their results are presented. At this point,only a single, under-utilized part of the system does not comply with DBPRStage 2 requirements and proposed corrective action for this area is alsopresented. [Pontius(1999)] Includes 13 references, tables, figures.

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Edition: Vol. - No. Published: 11/02/2003 Number of Pages: 13 File Size: 1 file , 300 KB