Direct Contact Membrane Distillation applied to the simultaneous treatment of two saline streams

Desalination by reverse osmosis (RO) allows to obtain two streams: one concentrated, rich in salt (brine), and the other very diluted (fresh water). The RO brine cannot be directly discharged into the marine environment, without altering the ecosystem. Therefore, its handling and disposal are the main challenges to face. In this work, Membrane Distillation (MD) in Direct Contact configuration (DCMD) was applied for the simultaneous treatment of solutions with NaCl concentrations of around 70 g/L at the permeate side (representing the RO brine) and around 18 g/L at the feed side, in order to obtain, at both sides, streams with concentration of seawater (around 35 g/L), so as to be discharged back to the sea. For this purpose, the experimental tests were carried out using a lab set up in which the module was equipped with a flat commercial membrane made in polypropylene (membrane pore size: 0.2 μm, thickness: 91 μm, membrane area: around 40 cm2). During the experiments, the effect on the permeate flux and feed/permeate conductivity of the feed temperature (40-50-60°C), permeate temperature and feed flow rate, while the permeate flow rate was fixed at 42 L/h, was investigated.