Retardation of wetting for membrane distillation by adjusting major components of seawater.

Wetting by fouling is phenomenon specific to membrane distillation (MD) and are regarded as challenges to the seawater membrane distillation (SWMD) process. To understand fouling and wetting, the influence of Mg and Sr crystals, which can potentially cause scaling, as well as Ca crystals deposited on the membrane surface were investigated. Mg(OH) and CaSO had significant impact on fouling and wetting. Even if CaCO and SrSO had no effects on fouling and wetting as single salts, CaCO and CaSO were dominant in synthetic seawater without Mg(OH). However, the occurrence of Mg(OH) scales became a cause for concern if Ca ion was removed from seawater for the prevention of fouling and wetting. Therefore, Mg as well as Ca should be removed for proper fouling and wetting control. NaOH/NaCO softening was used for the removal of Ca and Mg ions. In addition, based on the inhibition effects of Mg ions on Ca scales, a new pretreatment method involving the injection of MgCl to increase the Mg /Ca ratio was examined.