Low Molecular Weight Cut-Off Ultrafiltration Membrane for Arsenic Removal from Ground Water

1. Low Molecular Weight Cut-Off Ultrafiltration Membrane for Arsenic Removal from Ground Water IWA-8069 Satyendra Singh* , Gopal P. Agarwal Department of Biochemical Engineering & Biotechnology, Indian Institute of Technology Delhi, India E-mail:biotech882002@gmail.com IIT Delhi, India ABSTRACT In the present study removal of arsenic has been performed extensively with the excellent combination of high flux at low pressure with high rejection of arsenic. The effect of the presence of other naturally occurring co and counter ions like NaCl, Ca2+, K+, NO3- and SO42- on arsenic rejection has been studied. This membrane has shown 95% or even more rejection at 50 mg/L arsenic concentration, which decreased to 92 to 84 % in presence of individual co and counter ions. The drastic decrease in rejection of arsenic was observed in case of divalent counter ion (Ca2+), which is the major component of the ground water and Delhi municipal water (Tap Water). A tentative approach to explain the mechanism of arsenic rejection along with other ions through the modified UF membrane has been formulated. ABSTRACT ABSTRACT OBJECTIVES • Study the effect of naturally occurring anions (carbonate, sulphate and nitrate), and cations (Sodium chloride, Potassium and calcium) on the 50 ppm As (V) removal, using charged PAN based UF membrane system. • Study on the effect of Ca2+ ions as well as ground water (Delhi municipal water) on the arsenic rejection. MATERIALS AND METHODS A laboratory-scale plate and frame cross flow membrane filtration (CFMF) test unit procured from (RAYFLOW-RAYNOO21) TECH-SEP, Groupe Rhone-Poulenc was setup for the UF studies. The cross-flow cell of 100 cm2 active area was used and cross flow velocity (0.6-0.7 m/s) has been varied by pump. The transmembrane pressure (≤200 kPa) have been controlled by retentate flow and the whole set off experiments were carried out at ambient room temperature (27-30oC), pH ≥ 7. The experiments were performed with total recycle mode (Total recycle of permeate and retentate in feed reservoir) to keep the concentration of the feed solution constant. Fig. : Schematic representation of UF membrane module Table: Characteristics of membrane P2 RESULTS P1 Feed Tank • Effect of co and counter-ions • . • Effect of Ca2+ ion concentration • Effect of dissolved solid load on membrane Fig.: Comparison of rejection of As (V) (50ppm) alone,presence of other ions (NO3, SO4, NaCl, CO3 & PO4)(50 ppm each), tap water and 25X dil. tap water for E 90 (F) Membrane. Fig.: Effect of co-ions on rejection of arsenic (50ppm) using PAN E-90 modified membrane Fig.: Effect on As(V) rejection at different Ca2+ ion concentrations CONCLUSIONS • Removal of arsenate was 84- 92 % in presence of other ions except Ca2+ ion using modified PAN based UF membrane • The presence of Ca2+ ion showed drastic reduction in arsenic rejection, it may be due to electrostatic interactions may include the formation of ion pairs between counter ions and the fixed charge group in membrane matrix, which locally neutralize the membrane charge . • The ground water (TDS> 1125) effect decreased the overall arsenic rejection < 4%, because of the hardness of water