Removal of arsenic from contaminated groundwater by membrane-integrated hybrid treatment system

Experimental investigations were carried out to separate arsenic from contaminated groundwater by using three different types of nanofiltration membranes in a flat sheet cross flow membrane module with a pre-oxidation step for conversion of trivalent arsenic to pentavalent form. KMnO4 was used as an oxidising agent in the pre-oxidation step. Effects of pressure, iron concentration in groundwater, pH, and pre-oxidation on the performance of the membranes in terms of flux as well as percentage rejection of arsenic were studied. While transmembrane pressure was found to have strong impact on flux and retention of arsenic, pH and pre-oxidation exhibited strong influence on percentage removal of arsenic. Introduction of pre-oxidation step remarkably enhanced arsenic separation in a largely fouling-free membrane module. Overall arsenic removal increased from 50-63% to 97-100% for all the three types of membranes over a transmembrane pressure range of 5-12 kgf/cm2 on pre-oxidation of trivalent arsenic. With increase in pH from 3 to 10, arsenic rejection increased by 23% for NF-1, 33% for NF-2 and 26% for NF-20 membranes. Polyamide composite nanofiltration membrane fitted in a cross flow membrane module could successfully remove arsenic from contaminated groundwater with a pre-oxidation step.