Effect of Membrane Properties on Performance of Membrane Distillation for Ammonia Removal

Membrane distillation (MD) has received much attention in recent years as an alternative technology for the removal of volatile compounds from industrial waters. The microporous hydrophobic membrane utilised in MD allows only vapour passing through and the process selectivity is essentially determined by the liquid-vapour equilibrium conditions existing at the liquid-membrane interface. In this study, a series of asymmetrically structured polyvinylidene fluoride (PVDF) hollow fibre membranes were fabricated and tested for the removal of ammonia from simulated industrial wastewater. The asymmetric membranes contain very thin skin layer with macrovoids supported underneath. Hollow fibre MD modules with membrane area of 0.06 m have been assembled and tested for dilute aqueous solutions containing ammonia at concentrations <1000 mg/L. The membranes were characterised in terms of porosity, thickness, hydrophobicity, water permeability, surface roughness and zeta potential. Sweep gas MD configuration was employed for all experiments and >90% ammonia removal could be achieved. The results from the MD experiments were compared and the effect of membranes characteristics was discussed.