RO- Reverse Osmosis Basics of RO membranes Bisleri International Pvt Ltd- Bidadi 4th November 2022 2-3 hours training 1 L Osmosis Reverse Osmosis Dilute solution Concentrate solution Applied pressure Semi permeable membrane Osmosis & Reverse Osmosis 2 3 Reverse Osmosis • Cross flow filtration on Spiral Bound Reverse Osmosis Membrane Elements produces two streams (permeate and brine) from feed stream. • Dissolved and suspended solids are concentrated on brine stream. • Typical pore size of reverse osmosis membrane is < 0.002 microns 4 Assembly and parts of RO Element in vessel Video 5 Basic RO Terms • Salt passage and salt rejection • Cross Flow & Dead end flow. • Concentration Factor • Concentration polarization. • APF -average permeate flux - Combined permeate flow divided by the total membrane area in the RO unit. • Net Driving Pressure 6 Salt Passage & Salt rejection • SP - salt passage = Permeate TDS • Feed TDS • SR - salt rejection = (1-SP) x 100 7 F e e d P e r m e a t e D e p t h F i l t r a t i o n C r o s s f l o w F i l t r a t i o n M e m b r a n e F e e d P e r m e a t e C o n c e n t r a t e M e m b r a n e 3 S t r e a m s 2 S t r e a m s 8 Concentration Factor • Concentration Factor = Reject TDS = 100 • Feed TDS 100-R • R = Permeate Recovery % • At 50 % recovery, reject TDS is 2x higher than feed TDS • At 67 % recovery, reject TDS is 3x higher than feed TDS • At 75 % recovery, reject TDS is 4x higher than feed TDS • At 80 % recovery, reject TDS is 5x higher than feed TDS • At 90 % recovery, reject TDS is 10x higher than feed TDS 9 Net Driving Pressure • NDP is that pressure which remains to force water through the membrane. • NDP = Feed pressure • minus the average Osmotic Pressure • minus the average Delta P • minus the Permeate Back Pressure 10 Important Membrane Characteristics 1 sq ft Membrane Salt Rejection or Salt Passage 99 % Rejection or 1% Salt Passage 1000 mg/L 10 mg/L Specific Flux 0.5 GFD / PSI 100 psi 50 GPD 11 C o n c e n t r a t i o n P o l a r i z a t i o n F e e d P e r m e a t e C o n c e n t r a t e M e m b r a n e 12 Feed Water Limiting Condition • pH : 2-10 • Temperature : 40 deg C • Turbidity : 1 NTU (Recommended 0.1 NTU max) • Suspended solids : 1 ppm • SDI : 5.0 (Recommended 3.0 max) • LSI (CaCO3 saturation) : +2.5 (with antiscalant) • CaSO4% saturation : 240 (with antiscalant) • BaSO4% saturation : 800 (with antiscalant) • SrSO4% saturation : 6000 (with antiscalant) • Chlorine/Ozone : Nil • COD : 6-15 ppm • Oil & Grease : Nil • Heavy metals : 0.05 ppm 13 Problems faced in RO plant • Colloidal/ particle fouling • Coagulant precipitation • Scaling • Organic fouling • Bio fouling • Oxidative attack • Design/ Operation issues. 14 Solubility of Inorganic salts in water 15 Particulate Fouling 16 Surface Damage Due To Particle 17 Calcium Carbonate Scale 18 Calcium Sulphate Scale 19 Silica Scale 20