The Effects of Fluctuating Operation on Reverse Osmosis Membranes

Directly coupling renewable energy to reverse osmosis may be the most cost effective solution to supply potable water to remote and isolated areas that lack infrastructure and safe drinking water. These systems do not use batteries but rather operate only when sufficient energy is available and store any excess energy as water. Since reverse osmosis membranes are designed to be operated for continuous periods under constant power, it has been unclear how the fluctuating operation will affect the performance of the membranes. In these experiments, a small-scale reverse osmosis unit (maximum production 8 m3/day) was set up in the laboratory to continually recycle and treat a reservoir of artificial seawater (32 800 mg/L NaCl). The power of the high pressure pump feeding the reverse osmosis membranes is fluctuated corresponding to inputs of real wind data entered through an automated computer system. Measurements of pressure, permeate production and conductivity were continually recorded and used to determine if there were changes in the membrane permeability coefficient and salt rejection of the membrane resulting from fluctuating operation. After more than 650 hours of fluctuating operation, no deterioration of reverse osmosis membrane performance was observed.