The　potential　of　enhancing　As(III)　removal　was　investigated　in　a　pilot　study　for　the　process　of　oxidation,　precipitation　and　direct　sand　filtration　as　pretreatment　before　ultrafiltration.　The　pretreatment　effectively　facilitated　As(III)　removal　and　residual　arsenic　was　below　10　mu　g/L　for　membrane　effluent.　Sand　filters　exhibit　good　potential　for　removing　ferric　precipitates　with　adsorbed　arsenic,　and　membrane　filtration　is　more　significant　in　controlling　effluent　turbidity　in　this　process.　Permanganate　was　more　promising　than　chlorine　in　this　process,　mainly　ascribing　to　the　positive　seeding　effects　of　in　situ　formed　hydrous　MnO2(s)　and　the　formation　of　larger　floc.　A　bench-scale　study　demonstrated　the　remarkable　influence　of　in　situ　formed　hydrous　MnO2(s)　on　flocculant　aggregation.　The　widely　presented　silicate　(10　mg/L　as　Si)　showed　remarkable　negative　effects　on　arsenic　removal.　The　process　is　effective　in　enhancing　As(III)　removal　as　a　pretreatment　for　ultrafiltration;　however,　arsenic　removal　should　be　enhanced　while　silicate　presenting　to　assure　residual　arsenic　below　10　mu　g/L.