Technologies and Costs for Removal of Arsenic From Drinking Water

Table 2-14Adsorption Tests on GFHUnits Test 1 Test 2 Test 3 Test 4Raw Water ParameterspH 7.8 7.8 8.2 7.6Arsenate Concentration µg/L 100-800 21 16 15-20Phosphate Concentration µg/L 0.70 0.22 0.15 0.30Conductivity µS/cm 780 480 200 460Adsorption Capacity for Arsenate g/kg 8.5 4.5 3.2 N/DAdsorberBed Height m 0.24 0.16 0.15 0.82Filter Rate m/h 6-10 7.6 5.7 15Treatment Capacity BV 34,000 37,000 32,000 85,000Maximum Effluent Concentration µg/L 10 10 10 7Arsenate Content of GFH g/kg 8.5 1.4 0.8 1.7Mass of Spent GFH (dry weight) g/m 3 20.5 12 18 8.6N/D: not determinedThe competition of sulfate on arsenate adsorption was not very strong. Phosphate, however,competed strongly with arsenate, which reduced arsenate removal with GFH. Arsenate adsorptiondecreases with pH, which is typical for anion adsorption. At high pH values GFH out-performsalumina. Below a pH of 7.6 the performance is comparable.A field study reported by Simms et al. (2000) confirms the efficacy of GFH for arsenicremoval. Over the course of this study, a 5.3 mgd GFH plant located in the United Kingdom wasfound to reliably and consistently reduce average influent arsenic concentrations of 20 Fg/L to lessthan 10 Fg/L for 200,000 BV (over a year of operation) at an EBCT of 3 minutes. Despiteinsignificant headloss, routine backwashing was conducted on a monthly basis to maintain mediacondition and to reduce the possibility of bacterial growth. The backwash was not hazardous andcould be recycled or disposed to a sanitary sewer. At the time of replacement, arsenic loading on themedia was 2.3 percent. Leachate tests conducted on the spent media found that arsenic did not leachfrom the media.2-46