Water Filtration technologies

Transcription

1 Water Filtration technologies

2 Filtration Techniques

3 Filtration Overview Filtration = technique used for the separation of solids from liquids by interposing a filter, through which only the liquid can pass, oversize solids are retained. According to the size of contaminants to be retained, the process for separation and the filter pore size will be defined.

4 4 Water Monovalent Ion Multivalent Ion Viruses Bacteria Suspended solids Microfiltration Water Monovalent Ion Multivalent Ion Viruses Bacteria Suspended solids Ultrafiltration Water Monovalent Ion Multivalent Ion Viruses Bacteria Suspended solids Nanofiltration Water Monovalent Ion Multivalent Ion Viruses Bacteria Suspended solids Reverse Osmosis

5 Filtration Techniques Agenda Macrofiltration or particle filtration Microfiltration (MF) Ultrafiltration (UF) Reverse Osmosis (RO)

6 Macrofiltration

7 Macrofiltration = particle filtration Retention of particles which are of a visible size. Filter porosity is usually > 10 µm E.g. Backwashable Sand filters used as pretreatment at customers with poor feed water quality

8 Microfiltration

9 Microfiltration Definition Microfiltration = removal of contaminants by size filtration, typically in the field between 0.1 µm and 10 µm. UF Microfiltration Filtration 0.01 µm 0.1 µm 1 µm 10 µm Hepatitis Virus 0.02 µm Bacteria µm Blood cell 5 µm Use in lab water purification for removal of particulates & bacteria 2 types of microfilters: depth & screen filters

10 Depth Filters & Screen Filters Depth Filters Usually thick, made of fibers assembled together. Screen Filters Typically thin, made of a solid material pierced of similar holes Example: a fish net Example: fibers in cotton

11 Microfilters Retention Modes Depth Filters Screen Filters

12 Depth Filters vs Screen Filters Depth Filters Retention inside filter depth High capacity Good retention Screen Filters Retention on filter surface Low Capacity 100% retention (of contaminants larger than pore size) Use as a pretreatment, at the beginning of a purification process Use as a polisher at the end of a purification process

13 Examples Depth Filters Screen Filters Glass Fiber Filter Filter FCF

14 Hydrophilic & Hydrophobic Membranes Filters used to purify water hydrophilic filters (= they like water) Hydrophobic membrane filters (= they fear water) Usage for gas filtration.

15 Hydrophobic Filters Vent Filters Connected to the tank for air exit during fillingup by system air entrance &filtration while water is being taken out Degasser Inline with purified water flow and connected to a vacuum line Hydrophobic hollow fibers External part = water compartment Inside part = vacuum compartment Vacuum force attracts dissolved gasses out of water through the filter vacuum Hydrophobic screen filter Degassed Water

16 One more thing Your colleagues working with Life Science are specialized in filtration Don t hesitate to ask them your filter questions even you are from Waste Water Department

17 Ultrafiltration

18 UF Principle Definition Ultrafiltration = similar to standard filtration technique with membrane pores of a suitable size to remove molecules or viruses. membranes are characterized by their Nominal Molecular Weight Limit (NMWL) = the weight of the smallest molecules retained. Principle Pressure required High molecular weight solutes retained (based on the filter NMWL) Lower molecular weight molecules (<1kDa), salts & water molecules pass through

19 Reverse Osmosis

20 Osmosis Phenomenon Description: physical movement of a solvent (water) through a semipermeable membrane based on a difference in chemical potential. Table salt water Reverse Osmosis Pressure Even chemical potential diffusion Different chemical potential Osmosis The greater the pressure the more rapid the diffusion of water Water movement by diffusion of water molecules through semipermeable membrane

21 Reverse Osmosis vs Filtration Similar to filtration treatment process BUT Key differences: Filtration main removal mechanism is based on size exclusion due to the pore size of the filter Active layer (1 µm polyamide) Reverse osmosis involves a diffusive mechanism separation efficiency depends on: contaminant concentration, pressure water flow rate. RO requires : a semipermeable membrane (no visible pores) high pressure to revert the natural osmosis flow & increase water molecule diffusion, for purification efficiency Porous Support Pressurized Feed Water SEM Picture of an RO membrane cut through

22 Reverse Osmosis Principle RO membrane efficiency needs sufficient pressure (> 5 bar): Inorganic ions rejection: 95% 99%, if weakly ionized (e.g. Na ~95%) or strongly ionized (e.g. Fe 3 ~99%) Particles, bacteria & organic molecules (MW > 200Da): > 99% RO cartridge Pressurized Feed Water Ions 95% 99% Organic mol. Particulates Bacteria > 99% Permeate Type 3 water Reject RO membrane

23 Reverse Osmosis Tangential Flow To help limiting contaminant accumulation on RO membrane tangential feed water flow to take contaminants away RO cartridge Pressurized Feed Water Permeate Type 3 water Reject RO membrane

24 Reverse Osmosis Tangential Flow Feed Water Membrane Reject Permeate

25 Spiral RO Cartridge and FloClear Filter Feed Water tangential flow RO Cartridge Feed Water Inlet Sanitization Port Conductivity Cell (feed) Water Reject MILLIPORE Reverse Osmosis Element MILLIPORE Reverse Osmosis Element Spiral RO Membrane Part # PF05099 Rev 1196 Spiral RO membrane Part # PF05099 Rev 1196 RO Cartridge in Housing Reject Permeate Membrane rinsing during 2h4h to avoid permeate contamination Permeate Outlet

26 RO Efficiency Ionic Rejection RO efficiency is estimated by tracking its efficiency in rejecting ions : Conductivity measured upstream and downstream of the RO (at 25 C) Calculation of % of feed () permeate conductivities = % ionic rejection Ionic rejection increases with feed pressure increase, up to ~5 bar max ion rejection RO cartridge Clean Water P= min 5 bar Ions 95% 99% Permeate Cleaned standard water Reject

27 RO Permeate Flow Permeate flow F proportional to feed pressure P: if P1 > P2 F1 > F2 Permeate flow F increases with feed temperature T: if T1 > T2 F1 > F2 P1 > P2 Pressurized Feed Water T1 > T2 RO cartridge water diffusion F1 > F2 Permeate Flow F1 > F2 Flow restriction Reject Note: Salt diffusion with temperature % ion rejection when temp

28 RO Recovery RO recovery Amount of feed water required to produce a volume of purified water Recovery = 100 x (permeate flow / feed water flow ) RO cartridge Pressurized Feed Water Permeate Reject RO Recovery 42 L/h = 100 x (3) = 6.6 % (45)

29 RO Recovery Optimized RO recovery by addition of a recovery loop part of RO reject is diverted and reused to feed the RO membrane lower feed water quality = more challenging conditions RO cartridge Pressurized Feed Water Permeate Recovery Loop Reject

30 Water Waste Improving Recovery System Recovery 10.6 % Membrane recovery 10.6 % 2,400 galons/h 400 galons/h 2,000 galons/h If no recirculation System Recovery = Membrane recovery (for 1 membrane)

31 RO Recovery Optimized RO recovery by addition of a recovery loop part of RO reject is diverted and reused to feed the RO membrane Benefits: Water savings, Reduction on running costs Lower cleaned water quality = more challenging conditions Pressurized partial cleaned Water RO cartridge Permeate Recovery Loop Reject

32 RO & Storage Still, RO purification is a slow process permeate storage (for enough water available in one go) RO cartridge Storage Tank Pressurized Feed Water Permeate Recovery Loop Reject

33 Reverse Osmosis Life Time

34 RO Membrane Life Time RO membrane life time decreases with time % ionic rejection slowly goes down. with the impact of feed water quality : Hardness scale deposit on its surface Chlorine chemical attack piercing holes Organic Molecules fouling by accumulation on its surface Particulates (& Colloids) fouling and scratches ionic rejection reduction / flow variations

35 Feed Water Quality Impact Feed Water Contaminants Effect on RO membrane Specification Prevention / Solution Particles Colloids (colloidal Silica) Fouling Mechanical damage (scratches if hard) coagulation Coating SDI<1012 (Silt Density index or Fouling Index) Flush / Prefiltration RO Clean B Organics Coating / Fouling TOC < ppb AC Flush RO Clean B Chlorine Piercing of the active layer by chemical attack [Cl 2 ] < 3 ppm Activated Carbon Hardness & CaSO 4 (Ca/MgCO 3 ) crystal precipitation Scale fouling Large RiOs/Elix LSI< 0.3 Softening agent RO Clean A Iron & Manganese Hydroxides / Oxides precipitation fouling Tap: Fe< 50 ppt Mn < 20 ppt RO Clean A Softener Aluminium & Silicate (ionic form) Precipitate fouling Tap: Al < 50ppt RO Clean A Bacteria Biofilm formation biofouling Potable: < 100 cfu/ml Cl Sanitization / AC Silver / Flush High phs Decrease performances 4 < ph < 10 Adjustment before

36 RO Membrane Troubleshooting Issue : RO ionic rejection and / or flow rate decrease prematurely. If Ionic rejection is <92%, the RO membrane should be replaced Option : before replacing the cartridge, choose between 2 curative chemicals : RO clean A if likely to be mineral scaling (drilled well water, highly conductive water, hard / high LSI water) RO clean B if likely to be organic fouling (surface water, low conductivity water, soft water, high SDI water) might be too late). Partial recovery of flowrate & ionic rejection (as a function of time: it Offer the customer to : perform the operation on a regular time base. have additional pretreatment (softener or activated carbon/depth filter) if the RO life time is still not good enough.

37 RO Membrane Protection Cleaning Agents RO Clean A RO Clean B Chlorine tablets Warning ROClean A Warning ROClean B FloClear FloClear ZWACID012 ZWBASE012 ZWCL01F50 Ammonium Bifluoride RO Clean A Acid Trisodium Phosphate RO Clean B Base Sodium Dichloroisocyanurate Sodium Bicarbonate Adipic Acid Encapsulated Powder Pouch (6g /unit 12 units/ box) Non Woven Polyethylene Tissue Pill ( 5g/unit 45 units/ box)

38 3 Chlorine & Chloramines Chlorine is the enemy of Polyamide RO membranes as chlorine oxidizes the polyamide structure creating holes in the membrane. This is an irreversible procedure, affecting the performance of the RO cartridge in terms of rejection. Effect of chlorine in water: Chlorine reacts with water to for hypochlorous acid CL2 H20 HOCl H Cl Formation of Hypochlorous acid (H2OCl) is favored by low ph. The hypochlorous acid dissociates into hypochlorite ion at a higher ph. HOCl OCl H Hypochlorous acid has very strong bactericidal properties. It can penetrate the cell walls of bacteria and disrupt the cell. Hypochlorite ions are 100 times more oxidative than hypochlorous acid. High ph favors oxidation of RO cartridge with chlorine. High ph is not favorable for killing bacteria. Low ph is more favorable for killing bacteria. Low ph is less favorable for oxidization of RO cartridges. Chlorine is introduced into water as Sodium hypochlorite. (NaOCl) NaOCl H20 NaOH HOCl As the ph increases, more and more hypochlorite ions are formed. At ph 7.5 the amount of hypochlorous acid and hypochlorite ions are equal. At a ph of 10, hypochlorite ions are most abundant. Hence it is advised to sanitize the RO membrane at a ph around 7. This ensures enough hypochlorous acid for disinfection, but not too much hypochlorite ions, which are destructive to the Polyamide membrane.

39 RO Membrane Protection To save RO membrane life time, protection is added into our systems: System Flush = High flow of feed water going over RO membrane surface to take contaminants away and limit fouling Sanitization = to degrade the biofilm growing & gradually fouling RO surface FloClear pretreatment pack upstream the RO membrane = combination of 3 purification technologies to remove chlorine & organics to prevent scaling to remove particulates & colloids

40 RO : Flush vs Rinse Flush

41 RO : Flush vs Rinse Rinse

42 RO : Flush vs Rinse EDI or Tank Process

43 Reverse Osmosis Summary Benefits Limitations Up to 99% of water contaminants removed in single pass through the RO cartridge Easy tracking of efficiency by % ionic rejection monitoring Minimum maintenance Type 3 water produce RO membrane ages and is sensitive to main water contaminants *(1) it is a consumable Water waste * (2) Functioning dependent on feed temperature and pressure * (3) Storage required due to slow purification process * (4) * Limitations minimized thanks to our system improved design : RO (1) recovery loop (2) booster pump (3) optimized tanks (4)

44 Conclusion Filtration techniques: Microfiltration (depth & screen filtrations particulates & bacteria) Ultrafiltration (Filter Package pyrogenfree & nucleasefree water) Reverse Osmosis (complete technology removing up to 99% of all contaminants)

45 Ion exchange

46 Agenda Ionexchange theory Definitions Bead structure Ionexchange operation Binding Strength Limitations Ionexchange usage Service DI Single use EDI Softening

47 Definitions Ionexchange = deionization (DI) technique removal of charged compounds only! performed by ionexchange resins Ionexchange resin (= DI resins) = charged plastic beads Separation based on ionic bonding (attraction of opposite charges): Anionexchange resins remove anions (negatively charged) resin is positively charged Cationexchange resins remove cations (positively charged) resin is negatively charged

48 CationExchange Bead Structure Anionexchange beads: () fixed cation () counter ion Binding sites mainly inside Porous beads water needs to travel inside to be wellpurified Plastic Structure Fixed anion () Counter ion () Hydrating Water

49 CationExchange Bead Operation Plastic Structure Plastic Structure Fixed anion Counter cation Hydrating Water Contaminating cation

50 Binding Strength Calcium Ca 2 Copper Cu 2 Strong Binding Sulfate SO 2 4 Nitrate NO 3 Not all ions bind to the resin fixed ions with the same strength. Magnesium Mg 2 Potassium K Ammonia NH 4 Sodium Na Chloride Cl Bicarbonate HCO 3 Their ionic strength (linked to the number of charges) contributes to it. Hydrogen & hydroxyl ions bind with the lowest strength So they usually are the Counter ions Hydrogen H Weak Binding Hydroxyl OH

51 Cation & Anion Exchangers: Summary Mg 2 Fixed cation () Counter ion (OH ) Fixed anion () Counter ion (H ) CO OH 2 H 2 H 2 O

52 IonExchange Process End Exhausted resin Resin fouling All binding sites occupied by contaminating ions. expected end of resin life Binding sites still available inside but surface coating by other contaminants blocks the access. to be avoided with good enough feed

53 IonExchange Usage

54 D.I. Resin Bead Usage Na Cl Contaminated water flow through container Mixed bed DI resin in a container Gradual ion removal by exchange vs the counter ion: Na vs H / Cl vs OH Released H OH H 2 O

55 Service DI Mixed Bed Regeneration Tap Water DeIonized Tap Water Exhausted resins collected & returned to the plant for regeneration Regeneration: 1. Anionic & cationic resins separation (different densities) in big tanks 2. Resin immersion in strong acid or strong base solution to force counter ion back 3. Bottles are refilled with regenerated resin (/ fresh resin) 4. Regenerated bottles back at customers where exhausted ones are collected

56 Service DI: Benefits & Limitations Benefits: Low capital cost High instant flow rate (no reservoir) Good ionic quality: R > C Limitations: Operating cost transportation Still contaminated product water: tap water particulates, organic molecules & bacteria Additional contaminants due to regeneration: broken beads (fines), organic compounds & ions from other sources Conclusion: Process producing DI water Process inadequate to produce water (even less Type 1) Service DI water still contaminated with organics, colloids and particulates shorten life time water system consumables.

57 Single Use Mixed Bed Packs Single use mixed bed consumables contain virgin mixed bed ionexchange resin of high quality water Benefits producing very high water quality (high resistivity) high capacity and longer life cartridges Resin used in Disposable Single use = safety : no risk related to regeneration Limitation: good feed water quality required to avoid too high operating costs. More cleaned water

58 ElectroDeIonization EDI

59 EDI Technology Principle Allows passage of Anions Allows passage of Cations A C A C

60 EDI Technology Principle RO Feed Water A C A C

61 EDI Technology Principle RO Feed Water Cl Na A C A C H Cl Na Cl OH Na H Cl Cl Na Na Cl OH Na Waste Type 2 water

62 EDI Technology Principle RO Feed Water Cl Na A C A C H H Cl Cl Na Cl Cl Na Na Cl OH Na OH Na Conductive Carbon Beads Waste Cleaned water

63 Scaling due to high ph at cathode OH Generated at Cathode High Local Surface ph High Scale Potential standard flat cathode OH OH surface ph SOFTENER NEEDED Most Locations of Stations cathode surface

64 Carbon Beads: less steep ph gradient High Surface Area Cathode = Generation of hydroxyls in a larger volume standard flat cathode Reduces Local Surface ph surface ph Reduces Scale Potential NO SOFTENER NEEDED carbon bead cathode cathode surface

65 Activated Carbon

66 What is Activated Carbon? Activated Carbon (AC) = porous material prepared from organic material heated in specific conditions, with a high developed surface 2 types of AC: Natural AC Synthetic AC Controlled pyrolysis Coconut shell Polystyrene Beads Carbonization

67 Synthetic AC Operation Bead pores filled with water large contact surface with contaminants Organic molecules link to binding sites by weak Van der Waals forces

68 UV Light

69 Introduction UV light = wavelength from 100nm to 400nm Gamma Rays XRays UltraViolet Visible Infra Red Radio wavelength UV Light wavelength UV C nm UV B nm UV A nm UV light properties are used to help purifying water 1. Bacteria Destruction 2. Oxidation of organic molecules UV light produced by lamp containing small amount of mercury Exited mercury atoms emit relevant UV wavelengths

70 Bacteria Destruction UV 254 nm Relative Bactericidal Effect 100% 80% DNA 60% 40% 20% 254nm 0% Wavelength (nm)

71 Photooxidation process using a dual wavelength UV lamp power supply mercury vapor 185 / 254 nm lamp (18 Watts) optical quartz sleeve Water feed Oxidized H 2 O Hydroxyl radical Organic carbon Housing Inorganic carbon (CO 2, HCO 3 )

72 Organic Molecule PhotoOxidation Photooxidation Process: Water irradiation with UV 185nm 254nm free radical compounds Free radicals attack of the organic molecules organics oxidation Neutral organic molecule Charged organic molecule UV 185 nm 254 nm UV 185 nm 254 nm CO 2 H 2 O Short term effect: Apparition of charges on the organic molecule Long term effect: Fully degraded organic molecule by photooxidation

73 3 O 2 UV (185 ) CH OH 3 2 OH * 2 O 3 UV (254) H O 2 HCHO 2 H O 2 2 OH * 2 O 2 UV Action on Organic Contaminants H O 2 2 O * UV (254) 2 O 2 2 H O 2 2 HCOOH H O 2 2 OH * CO 2 2 H O 2 4 OH *

74 Organic Molecule PhotoOxidation Neutral Organic molecule UV 185 nm 254 nm Charged organic molecule CO 2 Mixed Bed IonExchange Resin H 2 O Long term effect: long enough contact time required between organic molecules & UV light for full degradation not often reached due to flow rate limiting the contact time Short term effect: charged organics collected on ionexchange resins downstream from UV lamp online main purification way.

75 Conclusion UV purification technology 254nm bactericidal effect 185nm 254nm organic molecule photooxidation Activated Carbon purification technology Natural AC reduction of chlorine level Synthetic AC adsorption of organic traces

76 Vacuum Degassing

77 Gas Content Common Dissolved Gases in water : Oxygen (O 2 ) / Nitrogen (N 2 ) / Carbon Dioxide (CO 2 ) Temperature Effect : dissolved gas solubility increases as temperature decreases : Temperature Gas solubility Pressure Effect : dissolved gas solubility increases as gas pressure increase above water. Pressure Gas solubility water temperature increase spontaneous degassing vacuum (= reverse pressure) degases water

78 Dissolved Gas Removal No chemical reaction with water : Gas easy removal with physical means (eg. vacuum) as for oxygen and nitrogen. Chemically react with water to some extent : Gases like CO 2, NH 3 and H 2 S Difficult to remove with vacuum after interaction. Usually removed with chemical means. Example: chlorine reduction by activated carbon. Water without dissolved gases does not stay degassed very long. CO 2 will dissolve in ultrapure water very quickly and form HCO 3 2 and H ions.

79 Aqueous degassing principle Vacuum* Degasser *generated either by a dual head pump or an reductor on the RO reject

80 GENERAL CONCLUSION

81 Contaminants IONS ORGANICS PARTICLES & COLLOIDS BACTERIA & VIRUSES GASES Purification Technologies DI RO UF MF AC UV converts organic molecules into CO 2 or charged molecules Still Not removed at all Totally removed

82 Thank you!