A Novel Forward Osmosis Desalination Process for Irrigation and Industrial Purposes

Abstract

The availability of clean water for agriculture has become a growing concern because of the increasing global water scarcity. Agriculture sector already accounts for around 70% of the total water withdrawals in the world whereas domestic and industrial water use is about 10% and 21% respectively. Desalinated water has high quality and irrigating with desalinated water would result in 24% increase in the crop yield and assist a 45% reduction in the current water irrigation volume simultaneously. However desalination is an energy intensive process and an expensive option. The current membrane and thermal desalination systems have many limitations, including high energy consumption and capital cost, especially for thermal methods, coupled with negative environmental impacts due to the discharge of brines and chemicals. Forward Osmosis (FO) promises to overcome most of the practical difficulties in conventional RO desalination process such as fouling, scaling, chemical treatment and high power consumption. In addition, FO process gives higher throughput with minimal environmental impact including minimal chemical additives and rejection of waste stream. Forward Osmosis (FO) process has the potential to increase the availability of freshwater both in coastal areas with limited resources and in areas where seawater, salinized groundwater and municipal wastewater are available. The novelty of FO process lies in using natural osmosis as a driving force for water to move across a semi-pearmeable membrane from a solution of low osmotic pressure (seawater) to a solution of high osmotic pressure (DS). The choice of draw solution (DS) has a large impact on the performance and viability of the FO process. The draw solutes should be able to generate high osmotic pressures and be completely regenerated using simple and energy efficient techniques.This study presents a novel FO process for producing irrigation water using thermolytic draw solution. The main energy intensive stage in FO process is the separation of draw solute from the freshwater. In this research, the concept of employing liquefied gas compounds as a draw agent has been investigated among 137 gaseous compounds by determining their high solubility in water. In this process a liquefied gas as DS with high solubility in water resulting high osmotic pressure has been used. The DS could be separated from water by changing the operating temperature and or pressure allowing for an efficient and complete removal of the DS. The modified FO process operates at low hydraulic pressure