Membrane Distillation (MD) as a desalination component in hybrid desalination process combinations for small Island Applications

Abstract The brine volume and environmental damage are key factors to consider desalination as a water source for small islands. Membrane distillation (MD) is still evolving to be used as a single source for desalination with constraints in pre-treatment and pore wetting. However reverse osmosis (RO) is optimised and thermal desalination is heat intensive. A combination of various desalination technologies with MD for seawater and brackish water at 35000ppm and 15000ppm is evaluated with low thermal renewable energy source. It is identified that while RO-MD combination for brackish and seawater desalination may have the least capital and operation cost, there isn’t much difference in levelised production cost considering increased recovery with combinations of RO-MD with Forward Osmosis (FO), Pressure Assisted Forward Osmosis (PAFO), Multi Effective Distillation (MED) and Counter Flow Reverse Osmosis (CFRO). The brine reduction rates are found to be halved with an increase in capital and operational cost of 50% and more. The unit cost of production for RO-MD is found to be INR 0.06 for brackish and INR 0.23 for seawater desalination. The addition of components will reduce the brine production, while increased capital and operational expanses stabilise unit cost of production.