PHASE INVERSION MODELING AND EXPERIMENTAL STUDIES ON POLYVINYLIDENE FLUORIDE/ BOEHMITE NANOCOMPOSITE MEMBRANE FOR ARSENATE ION REMOVAL FROM WATER

Abstract

Contamination of drinking water with arsenic is a severe threat that damages millions of people's health. Membrane based technology has been widely used in separation processes and has vast applications in wastewater treatment. Filtration combined with adsorption is beneficial, and this combination has been the commonly used, inexpensive and faster groundwater treatment technology. Polyvinylidene fluoride (PVDF) and its copolymers are becoming increasingly popular in water purification due to their outstanding thermal stability and high mechanical and chemical resistance properties. The selection criteria of these metal oxides or hydroxides are based on isoelectric point (pHIEP) since higher adsorption is exhibited by higher iso-electric point (pHIEP) value. Boehmite nanoparticles have a high isoelectric point value of 9.1 as given in the literature. PVDF/boehmite nanocomposite membrane was prepared using solvent casting at room temperature. A static adsorption test was conducted in a dead-end filtration setup, and the best rejection was obtained for Al/As ratio of 200:1 as 65% in a 1-hour duration. The water flux of the membranes was in the range of 62 to 270 L/m2h. The key component of solution thermodynamics is the solubility parameter. The solubility of boehmite nanoparticles was determined experimentally for 20 different solvents using the HSP method. The calculated solubility parameter was found as 33.08 MPa1/2. The binodal curve was located on the ternary phase diagram using Flory Huggin's theory. Thermodynamic enhancement and kinetic hindrance were calculated to predict the membrane morphology. The binodal curve shifts towards the solvent axis, which indicates the increase in the number of pores. The porosity of the membrane was theoretically increased with the addition of filler and agreed with experimental characterization. PVDF/ boehmite composite membrane was prepared using a non-solvent induced phase separation (NIPS) method. Filtration was done on continuous flow NF filtration setup and the membrane has shown the highest removal of 55% from 100 ppb arsenic solution with a flux of 3.5659 L/m2.hr.