In Japan, deep seawater has been a valuable resource for food industries
in particular, deionized deep seawater is widely used for bottled mineral water. However, concentrated deep seawater, a byproduct of the deionization process, has no current applications. In this study, we produced highly concentrated deep seawater using a novel membrane distillation system and cultivated the well-known halotolerant microalga Dunaliella salina, which is a rich source for β-carotene, using the distillation products. The proposed membrane distillation system consisted of two glass compartments (feed and permeate sides) and a polytetrafluoroethylene (PTFE) membrane. NaCl concentration from 5.2 to 12.3% was effectively achieved by maintaining the feed side at 36°C and the permeate side at 15°C
the water flux through the PTFE membrane was 0.4 t/day/m 2. The highly concentrated deep seawater produced from the distillation system was used to cultivate D. salina by adding only nitrogen and phosphate sources. These results suggest that this membrane distillation system is useful in manufacturing highly concentrated deep seawater that can be used as a medium for D. salina cultivation.
