Application of low-pressure nanofiltration coupled with a bicycle pump forthe treatment of arsenic-contaminated groundwater

A nanofiltration (NF) membrane process coupled with a bicycle pumping syste m was examined by using arsenic-contaminated tube well water in a rural are a of Bangladesh. It was operated under the conditions of low recovery and l ow operational pressure. It was proposed using both permeate and concentrat e of NF membranes for drinking water and smother purpose. Rejection charact eristics of arsenic compounds such as arsenite [As(III)] and arsenate [As(V )] were also investigated. Arsenite, a neutral solute at pH 8, showed lower rejection than arsenate, which existed in ionized forms at pH 8. In this s ense the pre-oxidation of arsenite to arsenate was necessary to obtain safe r drinking water using the NF process. Furthermore, the reverse osmosis (RO ) process could be operated under the conditions of high operational pressu re at 4MPa by using a bicycle pedal pump. Rejection of arsenite and arsenat e with the RO membrane was over 95%. However, treatment of concentrate with a high concentration of arsenic might be necessary for the application of the RO process where recovery was obtained at 66%. A high recovery of 66% w as delivered at three times a higher concentration of arsenic in concentrat e than feed water. Consequently, a low-pressure NF process with the pre-oxi dation of arsenite to arsenate or the RO process coupled with a bicycle pum ping system could be applied to the treatment of arsenic-contaminated groun dwater in areas where electricity supply is not efficient or feasible.