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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

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3.6.3 Direct FiltrationDirect filtration is a modified C/F treatment process utilized <strong>for</strong> source waters with lowinfluent suspended solids concentrations. Because <strong>of</strong> the low solids content, settling is not required<strong>and</strong> coagulation is followed immediately by filtration. Direct filtration includes all <strong>of</strong> the typical C/Fprocess elements with the exception <strong>of</strong> flocculation <strong>and</strong> sedimentation. Source waters with highinfluent As(III) concentrations may require pre-oxidation <strong>for</strong> conversion <strong>of</strong> arsenite to arsenate. Preoxidationtechnologies are discussed in Section 3.5. Direct filtration is unlikely to be installed solely<strong>for</strong> arsenic removal. The technology may not be able to achieve high removals <strong>of</strong> arsenic. Designcriteria are not presented <strong>for</strong> direct filtration.3.6.4 Coagulation Assisted Micr<strong>of</strong>iltrationCoagulation assisted micr<strong>of</strong>iltration is another modified C/F process wherein micr<strong>of</strong>iltrationis used in place <strong>of</strong> a conventional gravity filter. The process includes all coagulation, flocculation,sedimentation, <strong>and</strong> micr<strong>of</strong>iltration. Coagulation assisted micr<strong>of</strong>iltration is capable <strong>of</strong> removingsmaller particle floc which results in decreased coagulant dosage <strong>and</strong> increased plant capacity.Source waters with high influent As(III) concentrations may require pre-oxidation <strong>for</strong> conversion <strong>of</strong>arsenite to arsenate. Pre-oxidation technologies are discussed in Section 3.5.Very Small Systems (Less than 0.10 mgd)Capital <strong>and</strong> O&M costs <strong>for</strong> very small systems <strong>for</strong> the coagulation portion <strong>of</strong> this process weredeveloped using the VSS Model. The C/F design parameters given in Section 3.6.1 were used hereas well, however no polymer addition was assumed due to the tendency <strong>of</strong> some membranes to foulwhen used with polymer. Very small system costs also include a 20 mg/L sodium hydroxide dose toadjust process pH. Micr<strong>of</strong>ilter specifications <strong>and</strong> cost estimates were developed based on vendorquotes <strong>and</strong> case studies. These costs were then added to the C/F cost estimates.3-28

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