Abstract
The present work aims to study forward osmosis process using different kinds of draw solutions and membranes. Three types of draw solutions (sodium chloride, sodium formate, and sodium acetate) were used in forward osmosis process to evaluate their effectiveness with respect to water flux and reverse salt flux. Experiments conducted in a laboratory-scale forward osmosis (FO) unit in cross flow flat sheet membrane cell. Three types of membranes (Thin film composite (TFC), Cellulose acetate (CA), and Cellulose triacetate (CTA)) were used to determine the water flux under osmotic pressure as a driving force. The effect of temperature, draw solution concentration, feed and draw solution flow rate, and membrane types, were studied with respect to water flux. The results showed an increase in water flux with increasing feed temperature and draw solution concentrations In addition, the flux increased with increasing feed flow rate while the flux was inversely proportional with the draw solution flow rate. The results showed that reverse osmosis membranes (TFC and CA) are not suitable for using in FO process due to the relatively obtained low water flux when compared with the flux obtained by forward osmosis membrane (CTA). NaCl draw solution gave higher water flux than other draw solutions and at the same time, revealed higher reverse salt flux.
Highlights
Fresh water scarcity is a basic problem in many places in the world
According to figure 3, the water flux increase with temperature linearly and this attributed to decrease in viscosity of the feed water and this lead to increase in diffusion rate for water through the membrane outcoming in a higher permeability which is compatible with previous studies [19]
We notice that the effect of temperature on water flux is greater when using cellulose triacetate (CTA) membrane when compared with cellulose acetate (CA) and thin film composite (TFC) membranes
Summary
Fresh water scarcity is a basic problem in many places in the world. One of the most challenges of this century is the increasing for the demand of fresh water for drinking and other utilities such as food production and other industrial needs. In this research we describe the forward osmosis process by using three types of membranes (TFC, CA and CTA) and three types of draw solutions, one of them is inorganic (NaCl) and the two others are organic (sodium acetate and sodium formate). The main advantage of using organic salts as draw agent is to reduce the negative influence of the accumulation of draw solute in the feed side due to reverse salt flux and this phenomenon is desirable especially in osmotic membrane bioreactor (OMBR) systems for waste water treatment where the organic salt is biologically degraded in the reactor. The organic salt who have shorter carbon chain overcome the larger carbon chain when they are similar in cation species with the same osmotic pressure This phenomenon may be attributed to that the former has less ICP than the latter according to the higher diffusion coefficient. The thickness of the membrane is less than 50 μm
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