Forward osmosis

slides share the idea about forward osmosis

1. FORWARD OSMOSIS Presented By: MOHIT KUMAR (18FET208) NISHANK WAGHMARE (18FET211) 1

2. O smosis is defined as the net movement of solvent molecules across a selectively permeable membrane driven by a difference in osmotic pressure across the semipermeable membrane . Osmotic pressure  is the minimum pressure  which needs to be applied to a solution to prevent the inward flow of its pure solvent  across a semipermeable membrane. Π = iMRT where,   i   is van 't Hoff factor , M is molar concentration , R is the  ideal gas constant , T  is the temperature in  kelvin . INTRODUCTION 2

3. 3 OSMOTIC PROCESSES

4. 4 Osmotic Solutions There are 3 types of osmotic solutions:

5. The FO process results in concentration of a feed stream and dilution of a highly concentrated stream (referred to as the draw solution ). Forward osmosis membranes are of the asymmetric composite type- active layer (typically 100-200nm in thickness) support layer (typically 100-200μm in thickness) 5 Forward osmosis process

6. The general equation describing water transport in FO, RO, and PRO is J w = A(σ π − ∆P ) where Jw is the water flux , A the water permeability constant of the membrane, σ the reflection coefficient ∆P is the applied pressure. In FO ∆P = 0 The reflection coefficient describes the ability of a membrane active layer to preferentially allow solvent permeation over solute permeation σ = /   6

7. Concentration polarization is the build-up of concentration gradients both inside and around forward osmosis membranes during operation. 4 types of concentration polarization  two main categories : External concentration polarization (ECP)   Internal concentration polarization (ICP ) A nd two sub-categories; Dilutive Concentrative 7 CONCENTRATION POLARIZATION

8. Modules Packing density Advantages disadvantages Plate and frame below 100 m 2 /m 3 ease of operation in case of high amounts of fouling agents large footprint Spiral wound up to 600 m 2 /m 3 suitable for large volume applications due to high packing density membrane fouling Tubular up to 500 m 2 /m 3 ease of cleaning, replacement and ease of operation tube wall thickness might limit the water flux performance Hollow up to 1600 m 2 /m 3 Ideally suitable for high volume applications prone to fouling with high solid loadings 8 M embrane modules in Forward osmosis

9. MODERN APPLICATIONS OF FORWARD OSMOSIS Waste water treatment and water purification Seawater desalination Food processing Pharmaceutical industry 9

10. REFERENCE Achilli , A., Cath , T.Y., Childress, A.E. (2010). Selection of inorganic-based draw solutions for forward osmosis applications, Journal of Membrane Science, 364, 233-241 . Cath , T.Y., Childress, A.E., Elimelech , M . (2006). Forward osmosis: principles, applications and recent developments. Journal of Membrane Science , 281 , 70-87 . Tang, C.Y., She, Q., Lay, W.C.L., Wang, R., Fane AG. (2010). Coupled effects of internal concentration polarization and fouling on flux behavior of forward osmosis membranes during humic acid filtration. Journal of Membrane Science , 354, 123-133 . 10