Technologies and Costs for Removal of Arsenic From Drinking Water
Technologies and Costs for Removal of Arsenic From Drinking Water
Technologies and Costs for Removal of Arsenic From Drinking Water
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
3.7.2 Granular Ferric HydroxideGranular ferric hydroxide is a technology that may allow <strong>for</strong> very long run length without theneed <strong>for</strong> pH adjustment or pre-oxidation. It has been demonstrated <strong>for</strong> full-scale arsenic removal inEngl<strong>and</strong> (Simms, et. al., 2000). It was not designated a BAT because <strong>of</strong> the lack <strong>of</strong> published datashowing per<strong>for</strong>mance <strong>for</strong> a range <strong>of</strong> water qualities. Also, there is little published cost data, so costsare difficult to evaluate <strong>and</strong> are not presented.3.8 ION EXCHANGE PROCESSES3.8.1 Anion ExchangeIon exchange (IX) is a physical/chemical treatment process in which an ion on the solid phase(IX resin) is exchanged <strong>for</strong> an ion in the feed water, thereby removing contaminants from the feedwater. The IX removal mechanism is discussed in detail in Chapter 2. Ion exchange resin can befouled by suspended <strong>and</strong> dissolved contaminants in the feed water. If the feed water containssuspended solids the IX process will need to be preceded by a pretreatment process, typically multimediafiltration. Also, source waters high in As(III) concentration may require pre-oxidation <strong>for</strong>conversion <strong>of</strong> arsenite to arsenate. Pre-oxidation is discussed in Section 3.5. Neither pre-oxidationnor pre-filtration have been considered as part <strong>of</strong> the costs developed in this section. It is furtherassumed that corrosion control measures are not required because the pH is not significantly affectedby the process, especially when blending can be utilized.Sulfate concentrations in the influent water significantly affect the capacity <strong>of</strong> the IX resin withrespect to the removal <strong>of</strong> arsenic. Clif<strong>for</strong>d (1995) estimated bed volumes <strong>for</strong> 10 percent <strong>and</strong> 50percent breakthrough <strong>of</strong> influent arsenic as a function <strong>of</strong> influent sulfate concentration. Figure 3-15shows the bed volume <strong>and</strong> sulfate relationship estimated by Clif<strong>for</strong>d (1995). Using this figure, theregeneration frequency <strong>for</strong> an IX column can be estimated <strong>for</strong> the entire range <strong>of</strong> sulfate concentrationbased on the upper bound concentration. This is a very conservative assumption <strong>and</strong> underestimatesrun length <strong>for</strong> systems with lower sulfate concentrations in the range. The run length until regenerationis the critical factor in estimating the O&M cost. Capital costs will be marginally affected by changesin bed volume to regeneration.3-47
Change language