Effects of pH and temperature on forward osmosis membrane flux using rainwater to dilute cooling water

Cooling water plays an important role in maintaining proper temperatures for many industrial processes. To compensate for water loss and maintain sufficient cooling water quality, fresh water must be added to the circulating system.

In this US–Chinese study, researchers evaluated the feasibility of forward osmosis (FO) using rainwater as the makeup water source for the cooling water.

It was determined that the average water flux was 1.75 L/(m2h) at 23°C, and decreased gradually to 0.65 L/(m2h) after the draw solution was diluted four times.

Although the changes in pH had a small direct effect on the water flux, the existence of sodium hydroxide (NaOH) would promote the dissolution of more carbon dioxide into the feed solution, and thus inhibit the permeation process.

However, the temperature showed a notable effect on the water flux. By increasing the temperature of the draw solution from 3°C to 50°C, the membrane flux increased approximately 10 times.

During the extended operation, no flux decrease was observed as a result of membrane fouling, even when 50 mg/L kaolin or 25 mg/L sodium alginate was added to the feed solution.

Desalination, Volume 351, 15 October 2014, Pages 70–76.