Membrane distillation crystallization for simultaneous recovery of water and salt from tannery industry wastewater using TiO2 modified poly(vinylidene fluoride-co-hexafluoropropylene) nanocomposite membranes

Abstract

Membrane distillation crystallization (MDCr) is a promising technology for simultaneous water recovery and salt crystallization from tannery industry wastewater. We synthesized TiO2 modified poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanocomposite flat sheet membranes to treat tannery industry wastewater by MDCr. The influence of TiO2 nanoparticles morphologies on membrane performance (salt rejection and water flux) was investigated. The nanocomposite membranes were analyzed for surface morphology, thermal stability, porosity, water flux, and salt rejection. It was demonstrated that the TiO2 modified PVDF-HFP nanocomposite membrane showed improved hydrophobicity, porosity and number of pores; thus, water flux significantly increased without any deterioration in salt rejection. Among different membranes, decanoic acid-modified TiO2 nanoparticles (bipyramidal morphology) nanocomposite membrane (M-1B) showed 6.1 kg m−2 h−1 water flux with ~100% salt rejection with mixed synthetic salt solution (1% NaCl and Na2SO4, each) feed. Using real tannery industry wastewater, the M-1B membrane showed 5.9 kg m−2 h−1 water flux and 99.97% salt rejection. The crystallization of salts revealed cubic NaCl crystals and monoclinic Na2SO4 crystals in the wastewater. The XRD spectra revealed a high purity of salts and ruled out any co-crystallization. These findings suggested the potential candidature of the M-1B membrane for the treatment of tannery industry wastewater by the MDCr process. The recovered salt and water can also be re-used in the tannery industry.