Permitting Issues in Seawater Desalination: Examining the Microbial and Disinfection Byproducts Rules

摘要

The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), developed to fulfill requirements set forth in the Safe Drinking Water Act (SDWA) Amendments of 1996, proposes new standards for the removal of Cryptosporidium in drinking water plants in an effort to provide increased public protection from acute illness. The rule proposes a minimum removal/inactivation requirement of 3 log, with additional removal required dependant upon the source water concentration of Cryptosporidium oocysts. Although USEPA Water Supply Guidance documents indicate that it was not the intent of USEPA to apply surface water regulations to seawater, new data on Cryptosporidium viability in seawater and a trend towards the location of seawater facilities in estuarial waters challenge the premise of USEPA's guidance on seawater. Some primacy agencies have indicated that prudence may require that the LT2ESWTR be applied to seawater desalination facilities treating open water intakes, particularly if they are located in estuarial waters. As a result, existing and future coastal seawater desalination facilities in the USA must be prepared to comply with the requirements of the LT2ESWTR. Although RO can be used to achieve Cryptosporidium credit, the methods recommended are either technically difficult to achieve, and/or require the system to be taken off-line during the test. In either case, pursuance of Cryptosporidium removal credit for the desalination process is not recommended. Upon examination of the unit processes typically used for seawater desalination pretreatment, it appears that more than adequate removal credit will be achieved for bin 1 and bin 2 waters. A more advanced treatment processes, or a conventional process that produces particularly excellent water, may be granted sufficient credit to comply with bin 4 requirements - in such an event source water monitoring is not required for the facility.