Potentialities of thermal responsive polymer in forward osmosis (FO) process for water desalination

This work aims at assessing the technical feasibility and performances of the Forward Osmosis (FO), an emergent desalination process. Two FO processes with different draw solutions have been studied: the first one is based on Ammonium Bicarbonate (AB) and the second on poly (propylene glycol-ran-ethylene glycol) monobutyl ethers (PAGBs) with different molecular weight. The two solutes have different regeneration steps, but they adopt the same membrane separation process of the salt water. The comparison between the different processes is given in terms of recovery ratio, temperature and energy requirements. AB could be regenerated through column distillation at 99.63 degrees C and zeolite filter, while PAGBs could be regenerated at lower temperatures (77.2 - 83.6 degrees C) through gravity separation followed by a final step of nanofiltration. This study showed that PAGBs have great potential to desalinate water in an energy-efficient way, reaching minimum consumptions of 39.5 kWhth/ m3 and 0.5 kWhel/m3, even if the water recovery is not so high ( 24%). On the contrary, AB has shown higher energy consumptions ( 3.51 kWhel/m3, > 442 kWhth/m3). Finally, a comparison based on energy consumptions and recovery ratio with the mature desalination technologies is provided, showing the potentialities of the process when low temperature heat is available.