As Derek mentioned, the species of As matters if you are opting to use conventional treatment methods. Commonly the use of Greensand regenerated with KMNO4 (+ small amount of chlorine up stream) will oxidize As III to As V (RO works better on As V than it does As III) so post treatment with RO to remove the As V is likely required.
Published by Lawrence Jessup CWS VI,C.I., Director of Operational Excellence
As Derek mentioned, the species of As matters if you are opting to use conventional treatment methods. Commonly the use of Greensand regenerated with KMNO4 (+ small amount of chlorine up stream) will oxidize As III to As V (RO works better on As V than it does As III) so post treatment with RO to remove the As V is likely required.