Membrane Distillation Operated on Seawater Brines

Membrane Distillation (MD) has emerged in recent years as one of the most promising approach to seawater desalination. Specifically, a reduced sensitivity to concentration polarization, that represents a critical issue in Reverse Osmosis (RO), allows MD to operate at high concentration factors (CF), even up to NaCl supersaturation [1]. When treating seawater, scaling potential due to sparingly soluble salts dissolved is recognized as a critical problem. MD is a thermally-driven membrane operation, and scaling events are intensified by the inverse solubility of gypsum and calcium carbonate with temperature [2]. In addition, the presence of dissolved organic matter (DOM), in most part composed by humic substances derived from chemical and biological degradation of micro-organisms, increases the complexity of fouling phenomena. In the present study we investigated the performance of direct contact membrane distillation (DCMD) operated at high seawater concentration factors (from 4 to 6), with particular emphasis on: i) the kinetics of calcium carbonate scaling; ii) the effect of humic acid on calcite growth rate and on transmembrane flux stability; iii) the potential benefit of Submerged Ultrafiltration as pre-treatment.