Technologies and Costs for Removal of Arsenic From Drinking Water

2.4.12 Typical Design ParametersThrough extensive research, Clifford and others (1998) assembled typical operatingparameters and suggested options for ion exchange processes. Although many design parameters mustbe tailored to the specific treatment situation, Table 2-2 gives typical values and options.TABLE 2-2Typical Operating Parameters and Options for IX1.5 minute EBCT (15 gpm/ft 2 at 3 ft/day)0.5 - 1.0 M NaCl (1-2 eq Cl - /eq resin)Operate the column to a fixed BV endpoint (to prevent leakage)Regenerant Surface Loading Velocity should be greater than 2 cm/minRegenerant may be used 25 times or more (with Cl - concentration of 1 M maintained)Ferric coagulant should be used for Fe(OH) 3 •As from regenerant waste2.5 MEMBRANE PROCESSES2.5.1 IntroductionMembranes are a selective barrier, allowing some constituents to pass while blocking thepassage of others. The movement of constituents across a membrane requires a driving force (i.e. apotential difference between the two sides of the membrane). Membrane processes are oftenclassified by the type of driving force, including pressure, concentration, electrical potential, andtemperature. The processes discussed here include only pressure-driven and electrical potentialdriventypes.Pressure-driven membrane processes are often classified by pore size into four categories:microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). Typicalpore size classification ranges are given in Figure 2-1. High-pressure processes (i.e., NF and RO)have a relatively small pore size compared to low-pressure processes (i.e., MF and UF). Typicalpressure ranges for these processes are given in Table 2-3. NF and RO primarily remove constituentsthrough chemical diffusion (Aptel and Buckley, 1996). MF and UF primarily remove constituentsthrough physical sieving. An advantage of high-pressure processes is that they tend to remove a2-27