Technologies and Costs for Removal of Arsenic From Drinking Water

RO performance is adversely affected by the presence of turbidity, iron, manganese, silica,scale-producing compounds, and other constituents. Like NF, RO requires extensive pretreatment forparticle removal and often pretreatment for dissolved constituents. RO often requires pretreatmenteven for high quality source waters. RO has sometimes been used as a polishing step for alreadytreated drinking water. Pretreatment can make RO processes costly. Treated waters from RO systemstypically have extremely high quality, however, and blending of treated water and raw water can beused to produce a finished water of acceptable quality. This may reduce cost to some extent.RO is an effective arsenic removal technology proven through several bench- and pilot-scalestudies, and is very effective in removing dissolved constituents. Since the arsenic found ingroundwater is typically 80 to 90 percent dissolved, RO is a suitable technology for arsenic removalin groundwater. Several previous RO bench-scale and pilot-scale studies for arsenic removal aresummarized in Table 2-9. These studies indicate that RO can be an effective process for arsenicremoval, however, membrane type and operating conditions will affect removal and must be chosenappropriately. As with other processes, RO removes As(V) to a greater degree than As(III), somaintaining oxidation conditions may be important to the process.AWWARF (1998) performed bench- and pilot-scale RO testing. Short-term, single elementtesting and flat sheet testing were performed for a DK2540F RO membrane manufactured by DESALon a lake water and on spiked deionized water. Results from this testing are shown in Table 2-10.2-37