Membrane Filtration (MF / UF)

Transcription

1 Membrane Filtration (MF / UF) Mark White, PE, DEE Principal Engineer CDM Chicago University of Wisconsin Madison Water Treatment Plant Design October 26, 2011

2 Outline Membrane Fundamentals MF / UF Configurations MF / UF Operation Growth in Membrane Filtration Use Membrane Terminology Integrated Membrane Treatment Systems Membrane Regulations

3 Membrane Fundamentals

4 What is a Membrane? Thin barrier or film of material that allow certain substances to pass through while rejecting other substances. Feed Water Filtered Water (Permeate)

5 Drinking Water Membrane Treatment Feed Water Particles, Giardia, Cryptosporidium Some Viruses MF UF NF DOC, Hardness Minerals RO Water

6 Filtration Spectrum Dissolved salts Colloids Suspended solids Viruses Bacteria Org. macro. molecules Parasites mm polio virus smallest microorganism Cryptosporidium hair Reverse Osmosis Ultrafiltration Sand filtration Nanofiltration Microfiltration Figure Courtesy of GE ZENON

7 MF/UF Configurations

8 MF/UF Membrane Systems Multiple proprietary system with different dimensions, configurations, module types, and operating parameters.

9 MF/UF Membrane Systems Hollow Fiber

10 MF/UF Hollow Fiber Configuration Inside-Out Outside-In Greater prescreening Harsher cleaning Less prescreening Milder cleaning

11 Pressurized versus Submerged Systems Feed Water Feed Pump (0 to 50 psi) Treated Water Feed Water Permeate Pump (-2 to -12 psi) Treated Water Backwash Waste Backwash Waste Pressurized Membranes Submerged Membranes

12 Pressurized versus Submerged Systems Pressurized Membranes Greater Pressure Range Smaller Capacity Trains More Connectors/Valves Greater Footprint Usually for smaller WTP s Submerged Membranes Lower Pressure Range Higher Capacity Trains Less Connectors/Valves More Compact Footprint Usually for larger WTPs

13 MF/UF Hollow Fiber Membranes

14 MF/UF Hollow Fiber Membranes

15 Ideal MF/UF Membrane Materials Highly permeable Durable Resistant to chemical cleaning agents (e.g., chlorine) Inexpensive to manufacture Lightweight

16 Common MF/UF Membrane Materials Polyvinylidine Fluoride (PVDF) - Most Common Good permeability, resistant to chlorine and a range of ph levels, 5-10 year membrane life Polyethersulphone (PES) Polysulphone (PS) Cellulose Acetate (CA) Polypropylene (PP) Polyacrylonitrile (PAN) Ceramic - Focus for future systems

17 Ceramic Membranes = the future? Pros: Durable: year life; no broken fibers High flux (up to 175 gfd) Can accept high solids loading (including PAC) Chemically tolerant

18 Ceramic Membranes = the future? Cons: Expensive Heavy Subject to silica fouling Small number of installations

19 MF/UF Operation

20 MF/UF Filtration Cycle FLOW Start filtration Pressure Gradient

21 MF/UF Filtration Cycle FLOW FLOW Start filtration End filtration

22 MF/UF Filtration Cycle FILTRATE BACKWASH AIR SCOUR Initiate Backwash

23 MF/UF Filtration Cycle FLOW Start filtration

24 Dead-End Flow Entire Flow Passes Through Membrane Filter Cake Builds Up Requires Periodic Backwashing Fairly Good Quality Feeds Simple Operation Good Recovery >90% No Concentration of Feed Stream

25 Cross-Flow Flow is Pumped Across Membrane Creates Scouring Action Filter Cake is Reduced Higher Solids Feed Possible Increased Concentration of Feed Stream

26 Submerged Membrane Operation

27 Submerged Membrane Backwash

28 Backwash Draining

29 Growth in Membrane Filtration Use

30 Tremendous MF/UF Installation Growth From Development of a MF and UF Knowledge Base, AwwaRF2005

31 Tremendous MF/UF Installation Growth From Development of a MF and UF Knowledge Base, AwwaRF2005

32 Tremendous interest in membrane filtration in the Great Lakes area. Figure Courtesy of Siemens Water Technologies Figure Courtesy of GE ZENON

33 Typical MF/UF Treatment Objectives Turbidity Removal Advanced Disinfection Dissolved contaminant removal using combined treatment processes PAC Coagulation Oxidation Softening Ion exchange resins

34 Why use MF/UF treatment? Recent technological innovations Costs have been lowered High quality

35 Low Cost Membrane Installation Compare size to 2 football fields (each 360 ft long) Flocculation HDT: 45 min Conventional High Rate 35,000 ft 2 Membrane 12,000 ft 2 HDT: 10 min Sedimentation 50 MGD WTP Filtration 120,000 ft 2

36 Why use MF/UF treatment? Increased Regulatory Requirements Turbidity Waterborne pathogens DBP s

37 MF/UF Meets Treatment Requirements of the LT2ESWTR Filtrate turbidity < 0.05 NTU > 4-log Giardia / Cryptosporidium removal UF can provide 3.5- to 4-log virus removal MF can provide 0.5-log virus removal Removal credits valuable in reducing inactivation credits

38 Conventional Versus Membrane Treatment Jan-00 Jul-00 Jan-01 Jul-01 Jan-02 Jul-02 0 dity (NTU) Temp (deg F) Tap Turbidity d Plant Turbidity Membrane Plant Turbidity

39 Treatment Performance Conventional filtration turbidity relies on particle destabilization Membrane filtration turbidity is guaranteed, if the membrane is intact Membrane filtration operation targets optimal O&M costs

40 Why use MF/UF treatment? Expand / replace existing infrastructure

41 Manitowoc, WI Expansion of Existing Facilities

42 Manitowoc, WI Expansion of Existing Facilities

43 Why use MF/UF treatment? Socioeconomic Factors Aging population Greater sensitivity to microbial outbreaks

44 Waterborne Disease Outbreaks Tragic Events Year State/Territory Cause of Disease No. of People Affected 1985 Massachusetts Giardia lamblia (protozoan) 703 illnesses 1987 Georgia Cryptosporidium parvum (protozoan) 13,000 illnesses 1987 Puerto Rico Shigella sonnei (bacterium) 1,800 illnesses 1989 Missouri E. coli 0157 (bacterium) 243 illnesses / 4 deaths 1991 Puerto Rico Unknown 9,847 illnesses 1993 Missouri Salmonella typhimurium (bacterium) 650 illnesses / 7 deaths 1993 Wisconsin Cryptosporidium parvum (protozoan) 400,000 illnesses 100+ deaths 1998 Texas Cryptosporidium parvum (protozoan) 1,400 illnesses 1999 New York E. coli 0157 (bacterium) 150 illnesses / 1 death 2000 Ontario E. coli 0157 (bacterium) 1,000 illnesses / 7 deaths Source: HDR s Handbook of Public Water Systems

45 Sieve action rejects contaminants larger than the membrane pore size. 4 to 6 micron 0.1 micron pore size Giardia (4-14 micron) Cryptosporidium (4-6 microns in diameter)

46 Why use MF/UF treatment? Environmental Factors Increased use of lower quality water sources Deteriorating quality of existing sources Limited water supply

47 Orange County Water Factory 21, CA Secondary WW effluent, groundwater recharge 130 MGD

48 Changi, Singapore (Wastewater Reuse) NEWater potable reuse UF pretreatment to RO and UV

49 Membrane Terminology

50 Membrane Terminology Feed water: Influent stream to a membrane treatment process Filtrate (or permeate): Water produced by the membrane treatment process

51 Transmembrane Pressure (TMP) The driving force for the transport of water across MF and UF porous membranes. Difference in pressure across the membrane that provides the driving force for filtration TMP increases as membrane fouls TMP increases as temperature decreases Typical TMP range for MF/UF membranes is 5 to 50 psi

52 Transmembrane Pressure TMP (psi) Transmembrane Pressure Pressure in - Pressure Out Operating Hours

53 Transmembrane Pressure TMP (psi) Backwash Operating Hours Every 30 to 60 min. for 2 to 3 min. duration

54 Transmembrane Pressure TMP (psi) Maximum TMP Operating Hours

55 Transmembrane Pressure TMP (psi) Chemical Clean Operating Hours

56 Temperature Impacts on Viscosity Reduced capacity at low temperature due to increased viscosity 2 Temperature Effect on Water Viscosity Viscosity (cp) Water Temperature (C)

57 Membrane Flux Flux: Throughput of a membrane treatment system (surface loading rate) J = Q filtrate / A Where: Q filtrate = flow rate of filtrate or permeate A = active area of membrane Units of flux: gpd / ft 2 (gfd) or lph / m 2 (lmh) Typical flux range is 30 to 80 gfd

58 Temperature-Corrected Flux Used to normalize impact of temperature on performance to reference temperature (usually 20C) Flux (20C) = Flux (T1) X TCF TCF = Viscosity (T1) / Viscosity (20C

59 Permeability Permeability is the ability of a membrane to pass a substance (e.g., water) = Flux (20C) / TMP Typical units are gfd / psi

60 Recovery Percent of feed water converted to usable filtrate = Amount of filtrate produced over a given time, less amount of filtrate used for membrane cleaning processes divided by amount of feed water Typical recovery range is 90 to 97%

61 Membrane Fouling Build-up of materials on the membrane modules that increases the TMP and reduces capacity. Solids Organics (colloids, biogrowth, polymers, etc.) Inorganic precipitates (silica, iron, manganese, barium, etc.)

62 Membrane Fouling Hydraulically-reversible fouling: fouling removable using a backwash process Chemically-reversible fouling: fouling removable using a chemical cleaning processes Irreversible fouling: fouling not removable by backwashing or cleaning. This fouling permanently reduces the capacity of the membrane modules, eventually requiring their replacement

63 Membrane Fouling Source: Water Treatment Membrane Processes, AWWA, 1996 Chemical Cleaning Performed Transmembrane Pressure Hydraulically- Reversible Fouling Backwashing Operating Hours Chemically- Reversible Fouling Irreversible Fouling

64 Chemical Cleaning Processes Chemically-enhanced backwash (CEB) Frequent: every 1 to 7 days Short duration: ~ 30 minutes Low strength chemicals

65 Chemical Cleaning Processes Recovery clean (aka Clean-In-Place or CIP) Typically every 30 to 90 days Long duration: 2 8 hours High strength chemicals

66 Typical Cleaning Chemicals Hypochlorite (for chlorine-tolerant membranes) Citric acid Mineral acid (H2SO4, H3PO4, HCl) Surfactant Chelating agent NaOH Proprietary cleaners

67 Integrated Membrane Treatment Systems

68 MF/UF Treatment Process Design Membrane systems can be implemented at many stages within a treatment plant Pretreatment ahead of membranes is selected based upon: Raw water quality Treatment goals Site-specific constraints Pretreatment may be used to meet water quality goals or to improve the operation of the membrane system

69 Microstrainer Pretreatment of MF/UF Typically required for all MF/UF membranes to eliminate objects that can damage the membranes during vigorous air scour Shell fragments, gravel, pine cones, debris, etc. Microstrainer pore size: microns

70 Direct Filtration of MF/UF Direct filtration of MF/UF is cost-effective when turbidity removal and advanced disinfection are primary treatment goals Well-suited for water from the Great Lakes (Manitowoc, Kenosha, South Milwaukee, Two Rivers, Lake Forest, East Chicago and others) Suitable for highly turbid water RAW WATER STRAINER MF / UF DISINFECTION TREATED WATER

71 Coagulation Pretreatment of MF/UF Convert dissolved contaminant to solid phase so that they can be removed by the membranes Example contaminants: DOC, arsenic Washoe Co., NV Albuquerque, NM, College Wells Fernley, NV RAW WATER COAGULATION STRAINER MF / UF DISINFECTION TREATED WATER

72 Oxidation Pretreatment of MF/UF Precipitate iron and manganese so that they can be removed by the membranes Algonquin, IL RAW WATER OXIDATION STRAINER MF / UF DISINFECTION TREATED WATER

73 Softening Pretreatment of MF/UF Precipitate hardness ions and DOC so that they can be removed by the membranes Minneapolis, MN Marco Island, FL RAW WATER TREATED WATER SOFTENING / CLARIFICATION STRAINER MF / UF DISINFECTION

74 Clarification Pretreatment of MF/UF Some time clarification improves performance of MF/UF membranes, allowing higher flux or reducing membrane cleaning Reuse existing sed. basins Erie, PA RAW WATER TREATED WATER CLARIFICATION STRAINER MF / UF DISINFECTION

75 Filtration Pretreatment of MF/UF MF/UF membranes sometimes used as polishing step after conventional filtration Provides multi-barriers for advanced disinfection Racine, WI Appleton, WI Park Cities, TX RAW WATER COAGULATION/ FLOCCULATION PRE-TREATMENT CLARIFIER SAND FILTRATION MF/UF DISINFECTION TREATED WATER

76 Racine, WI (50 MGD MF) Existing 50 MGD conventional pretreatment facilities Filtered water benefits Inst.Flux Net Flux Flux (gfd) Conventionally Filtered Water Settled Water

77 Ozone and Membranes What order to put Ozone/GAC and Membranes? Membranes First Lower ozone demand Less clogging of GAC contactors Membranes are not final barrier to microorganisms (BAC) Ozone/GAC First Reduced membrane fouling Membranes final barrier to microorganisms Higher ozone demand Frequent GAC backwash

78 Santa Fe, NM (15 MGD) PREOZONE RAW WATER PRE-SED. COAG / FLOC CLARIFICATION STRAINER MF/UF OZONE TREATED WATER DISINFECTION GAC CONTACTOR

79 MF/UF as Pretreatment to NF/RO High-quality MF/UF feed improves operation of NF/RO membrane system Changi, Singapore

80 Membrane Regulations

81 LT2ESWTR MF/UF membrane filtration is approved technology for Cryptosporidium removal Membrane Filtration Guidance Manual provides design recommendations and integrity verification requirements.

82 Membrane Integrity Key to Ensuring High Quality Water Intact membrane fibers reject particles and pathogens larger in size than membrane pores. Integrity breaches allow unfiltered flow to enter clean water supply. Untreated By-Pass Figure Courtesy of GE ZENON

83 Integrity Monitoring Requirements LT2ESWTR & Membrane Filtration Guidance Manual: Three types of integrity monitoring required Product-Specific Challenge Testing Direct Integrity Testing Indirect Integrity Monitoring Once per product Daily (minimum) Continuous

84 Pressure Decay Test (PDT) Defect Membrane integral Lumen Air Pressure Membrane suspect Membrane wall Figure Courtesy of Siemens MEMCOR Time

85 Response to Integrity Breach Identification of breach location Visual Identification (Submerged Systems) Photo Courtesy of Siemens MEMCOR

86 Response to Integrity Breach Identification of breach location Visual Identification (Pressure Systems) Photo Courtesy of Pall Corporation

87 Response to Integrity Breach Identification of breach location Sonic Identification (Pressure Systems) Photo Courtesy of Siemens MEMCOR

88 Response to Integrity Breach Module repair Photo Courtesy of GE ZENON Photos Courtesy of Siemens MEMCOR

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