wastewater by soil aquifer treatment (SAT) so that it can be stored underground for eventual potable use The feasibility of SAT in the Phoenix area was studied with a small test project installed in 1967 and a larger demonstration project installed in 1975 The latter could be part of a future operational project that would have a basin area of 48 ha (119 acres) and a projected capacity of about 276 x 106 m3/year (73 x 109 gal/ year) Both projects were operated in the normally dry Salt River bed (Bouwer and Rice, 1984)

Planned augmentation of surface water supplies with reclaimed water is being investigated in both California and the eastern United States for different reasons San Diego is actively investigating the feasibility of augmenting its general water supplies with reclaimed municipal wastewater because of the high costs of importing water from other parts of the state and the lack of local water sources (see Box 1-6) In Florida, both water shortages and waste disposal requirements are generating increased interest in the use of reclaimed wastewater Increasingly stringent requirements regulating discharge to sensitive receiving waters have

Box 1-6 San Diego's Total Resource Recovery Project

San Diego, California, imports virtually all of its water supply from other parts of the state. New sources of imported water are not readily available, and the availability of existing supplies is diminishing. The city is thus actively investigating advanced water treatment technologies for reclaiming municipal wastewater that is presently being discharged to the Pacific Ocean. Preliminary experiments were conducted at the bench-scale (0.02 x 106 gal/day) Aqua I facility in Mission Valley from 1981 to 1986. the pilot-scale (0.3 x 106 gal/day secondary, 0.05 x 106 gal/day advanced) treatment Aqua II Total Resource Recovery facility operated at Mission Valley from 1984 through 1992. the full-scale demonstration Aqua III facility (1 x 106 gal/day secondary, 0.5 x 106 gal/day advanced) was constructed in Pasqual Valley and began full-time operation in October 1994.

The Aqua II pilot facility uses channels containing water hyacinths for secondary treatment, followed by a 50,000 gal/day advanced treatment system designed to upgrade the secondary effluent water to a quality equivalent to raw water for potable reuse. The tertiary and advanced process trains were selected in 1985 by a technical advisory committee in conjunction with the city. Tertiary to produce a low-turbidity water suitable for reverse osmosis feedwater was provided by a package water treatment plant, with ferric chloride coagulation, flocculation, sedimentation, and multimedia filtration. The system included ultraviolet light dissinfection, cartridge filtration, chemical pretreatment, reverse osmosis using thin-film composite membranes, aeration tower decarbonation, and carbon adsorption. The final process train produces water that meets U.S. drinking water standards.

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