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10.10 WATER PRODUCTION COSTS 233
FIGURE 10.2 Universal ultrafiltration rack that accommodates membranes from several manufacturers.
10.10 WATER PRODUCTION COSTS
At present, the overall cost of production of desalinated water using the membrane pre- treatment is typically 5%e15% higher than that for fresh water produced by desalination plants with conventional source water pretreatment. In some cases, such as conditions when the source water quality is highly variable and/or the cost and availability of land are at premium, membrane pretreatment may be more cost advantageous. Also, when source water quality is fairly high, the membrane pretreatment system could be designed quite aggressively and could have a clear capital and life-cycle cost advantage compared with con- ventional granular media filtration.
Key factors that are often underestimated or omitted when comparing granular media and membrane pretreatment systems are (1) the additional capital and O&M costs of the micro- screening system needed to protect the integrity of the pretreatment membranes; (2) the actual chemical costs and frequency of pretreatment membrane cleaning and chemically enhanced backwash; (3) the useful life and replacement costs of the pretreatment membranesdmost analyses assume 5 yearsdwhereas actual operational data show that membranes need to be replaced in approximately 3 years due to the loss of integrity; (4) the 5%e10% higher cost of project financing associated with the use of membrane pretreat- ment because of the long-term risk associated with the use of technology of limited full-scale track record and commoditization, especially for large-scale desalination plants.