ARSENIC REMOVAL FROM DRINKING-WATER DURING COAGULATION

The efficiency of arsenic removal from source waters and artificial fr eshwaters during coagulation with ferric chloride and alum was examine d in bench-scale studies. Arsenic(V) removal by either ferric chloride or alum was relatively insensitive to variations in source water comp osition below pH 8. At pH 8 and 9, the efficiency of arsenic(V) remova l by ferric chloride was decreased in the presence of natural organic matter. The pH range for arsenic(V) removal with alum was more restric ted than with ferric chloride. For source waters spiked with 20 mu g/L arsenic(V), final dissolved arsenic(V) concentrations in the product water of less than 2 mu g/L were achieved with both coagulants at neut ral pH. Removal of arsenic(III) from source waters by ferric chloride was both less efficient and more strongly influenced by source water c omposition than removal of arsenic(V). The presence of sulfate (at pH 4 and 5) and natural organic matter (at pH 4 through 9) adversely affe cted the efficiency of arsenic(III) removal by ferric chloride. Arseni c(III) could not be removed from source waters by coagulation with alu m.