MEMBRANES FOR WTPS JUSTIN RAK-BANVILLE, M.SC., P.CHEM., EP WATER AND WASTEWATER INFRASTRUCTURE WSP CANADA INC

Transcription

1 MEMBRANES FOR WTPS JUSTIN RAK-BANVILLE, M.SC., P.CHEM., EP WATER AND WASTEWATER INFRASTRUCTURE WSP CANADA INC

2

3 MEMBRANES BRIEF HISTORY 1956 to early 1970 s RO driver by desalination, no commercial MF/UF for drinking water During the 1970 s RO membranes with greater operating pressures were developed This resulted in considerable increases in energy cost Mid 1980s to early 1990 s Development of microfiltration (Memcor) and ultrafiltration (Aquasource) By the late 1980s, NF became established Low-pressure RO membranes were developed and came be known as NF membranes

4 MEMBRANES BRIEF HISTORY (CONTINUED) Early 1990s Membrane filtration costs 3x to 4x the price of conventional filtration and desalination costs were 10x Milwaukee Cryptosporidiosis outbreak in part drives innovation led by Dow, Memtec (Siemens), ZENON (GE), etc. Late 1990s Membranes become cost competitive, reduction in costs and increases in throughput Membranes become cost competitive with non-membrane technologies for many applications. Reducing wastage and reuse of water. Reducing cost of overall operation.

5 MEMBRANE USES FOR WATER TREATMENT Municipal Water Treatment Industrial High Purity Process Water Municipal Wastewater Treatment Residential Water Treatment Industrial Process Wastewater Desalination

6 STRINGENT WATER QUALITY Source: The Water We Drink: An International Comparison of Drinking Water Quality Standards and Guidelines David Suzuki Foundation, 2006.

7 PRIMER Membranes work by creating a physical separation

8 CREATING A PHYSICAL SEPARATION MOLECULAR WEIGHT CUT OFF (MWCO) USED TO CHARACTERIZE MEMBRANES Membranes with MWCOs ranging from 1 500,000 kda are commercially available, membranes with MWCO near 10 kda are most commonly used for water treatment. MWCO refers to the smallest average molecular mass of a standard molecule that will not effectively diffuse across the membrane. Ideally, a molecular must be at least 20x to 50x times smaller than the MWCO rating of a membrane to allow rapid, smooth diffusion. Many factors affect MWCO ratings. - Vary with membrane age, material, cleaning, temperatures, etc.

9 MEMBRANE PROCESSES Generally, there are four common types of membrane processes: Microfiltration Particle exclusion (> 0.1 µm) Ultrafiltration Macro-molecule exclusion MW between 2 kda 500 kda Nanofiltration Molecule exclusion (MW between 200 Da and 2 kda) Some multivalent ion exclusion Reverse Osmosis Ion exclusion (monovalent ions)

10 RELATIVE FILTRATION SPECTRUM

11 PILOT DATA ALS Sample ID #1 RAW - Metals only - Surface water body - Shallow - Water control structure - Feed by Boyne River #3 MICRO EFFLUENT #5 NANO EFFLUENT 10/16/2015 ALS ID L L L L Date Sampled 8/20/2015 3:00:00 8/20/2015 3:00:00 8/20/2015 3:00:00 PM PM PM Analyte Units LOR Water Water Water Aluminum (Al)-Total mg/l < < Antimony (Sb)-Total mg/l < Arsenic (As)-Total mg/l < Barium (Ba)-Total mg/l Beryllium (Be)-Total mg/l < < < Bismuth (Bi)-Total mg/l < < < Boron (B)-Total mg/l Cadmium (Cd)-Total mg/l < < Calcium (Ca)-Total mg/l Cesium (Cs)-Total mg/l < < < Chromium (Cr)-Total mg/l < < < Cobalt (Co)-Total mg/l < Copper (Cu)-Total mg/l Iron (Fe)-Total mg/l <0.10 <0.10 Lead (Pb)-Total mg/l Lithium (Li)-Total mg/l Magnesium (Mg)-Total mg/l Manganese (Mn)-Total mg/l < Molybdenum (Mo)-Total mg/l < Nickel (Ni)-Total mg/l < Phosphorus (P)-Total mg/l <0.10 Potassium (K)-Total mg/l Rubidium (Rb)-Total mg/l Selenium (Se)-Total mg/l < < < Silicon (Si)-Total mg/l Silver (Ag)-Total mg/l < < < Sodium (Na)-Total mg/l Strontium (Sr)-Total mg/l Tellurium (Te)-Total mg/l < < < Thallium (Tl)-Total mg/l < < < Thorium (Th)-Total mg/l < < < Tin (Sn)-Total mg/l < < < Titanium (Ti)-Total mg/l < < Tungsten (W)-Total mg/l < < < Uranium (U)-Total mg/l < Vanadium (V)-Total mg/l Zinc (Zn)-Total mg/l < Zirconium (Zr)-Total mg/l < < <

12 TYPES OF MEMBRANES LOW PRESSURE MICROFILTRATION (MF) ULTRAFILTRATION (UF) REMOVES: TURBIDITY VIRUSES BACTERIA PROTOZOA PARTIAL ORGANICS Microfiltration (Bacteria, fungi, etc.) Ultrafiltration (Viruses, etc.) HIGH PRESSURE NANOFILTRATION (NF) REVERSE OSMOSIS (RO) REMOVES: TURBIDITY VIRUSES BACTERIA PROTOZOA ORGANICS INORGANICS Nanofiltration (Dissolved organics, multivalent ions, etc.) Non specific microorganism removal (charge and size exclusion, MWCO) Reverse Osmosis (Monovalent ions, etc.) Pressure Increasing transmembrane pressure, decreasing membrane operational life

13 MEMBRANE THEORY OSMOTIC PRESSURE Attributed to several geochemical processes: Describes expected operational pressure of RO membrane Salinity, ppm TDS 5,000 20,000 35,000 70,000 80,000 30C 48 psi 201 psi 372 psi 744 psi 856 psi 15C 46 psi 191 psi 355 psi 708 psi 813 psi Π = Osmotic Pressure C = Concentration (mol/l) R = Gas Constant (L atm/mol K) T = Temperature (K)

14 DEAD-END AND CROSS-FLOW MODES Cross-Flow (NF/RO) Dead-End (MF/UF)

15 MEMBRANE FLAVORS TYPES OF MEMBRANES Spiral membranes Hollow Fiber/Tubular Membranes Surface area of spiral membranes is greater than tubular membranes greater treatment capacity

16 LOW PRESSURE MF/UF Dead end filtration Flux : 60 to 140 l/h/m² TMP: 0,2 to 1,5 bar Lifetime: 5 years

17 LOW PRESSURE MF/UF Mineral and organic fouling present at the membrane surface Fouling of particulate mater

18 HIGH PRESSURE NF/RO TERMS J v = Q p S Permeate flux describes the quantity of permeate produced during membrane separation per unit of time R = 1 C p C avg 100 Y = Q p Q f Salt rejection is a percentage which describes the amount of solute retained by the RO membrane. C avg is the average feed concentration, C avg =(C f +C c )/2 Recovery rate is defined as the fraction of the feed flow which passes through the membrane. It is usually expressed in percentage. TMP = P F + P c 2 P P Transmembrane Pressure of the membrane system is an overall indication of the feed pressure requirement; it is used, with the flux, to assess membrane fouling

19 TREE LAYOUT OF MEMBRANE FILTRATION Source: David Hendricks, Fundamentals of Water Treatment Unit Processes, IWA Publishing, 2013.

20 MEMBRANES AND ARSENIC MANITOBA GROUNDWATER Groundwater throughout the Province is typically good, however it is influenced by both natural and anthropogenic sources. Erosion and weathering of soils, minerals, etc., mining, industries, etc. Arsenic is found in different parts of the Province, and even in different parts of the same aquifer. Classified as human carcinogen GCDWQ MAC based on treatment achievability Manitoba Drinking Water Quality Standards Regulation MAX 0.01 mg/l (10 μg/l) ALARA

21 ARSENIC AND IT S MOBILITY IN GROUNDWATER Theories of arsenic mobilization: Oxidation of As bearing sulfides Desorption of As from oxides and hydroxides (oxygen, iron, aluminum) Release from geothermal waters Leaching of As from sulfides by carbonate Due to complexities and likely simultaneous processes, source identification is difficult. Substantial verification needed to distinguish mechanisms which release arsenic.

22 ARSENIC CYCLE Source: Microbial arsenic: from geocycles to genes and enzymes Rita Mukhopadhyay, Barry P. Rosen, Le T. Phung, Simon Silver FEMS Microbiology Reviews Aug 2002

23 ARSENIC AND IT S MOBILITY There are both organic and inorganic forms of arsenic found in nature. Arsenic is present in a number of different forms and oxidation states (-3, 0, +3, +5) In aqueous environments, dissolved arsenic is normally found as part of oxyanions in either arsenate (+5) or arsenite (+3) form.

24 ARSENIC AND MEMBRANE REMOVAL As 3+ and As 5+ are soluble and cannot be removed as ions by a MF or UF membrane. They ions and are much smaller than the typical pore sizes associated with MF/UF membranes. As 3+ has no net charge and thus is more difficult for membrane removal (i.e. As 2 O 3 common groundwater form) Often design to oxidize As 3+ to As 5+ for membrane removal. As 5+ has a net charge, facilitating removal. Alternative is to coagulate prior to MF Depends on design, scale, budget, blending, etc.

25 MEMBRANE ARSENIC REMOVAL Design Factors To Consider Water Chemistry ph As concentration As speciation Ionic strength Co-solutes Physical Parameters Pressure Temperature Flow rate Recovery Membrane Characteristics MWCO Membrane surface charge Salt separation ability Hydrophobicity Fouling

26 Raw at WTP: AUG-12: TEST As(III) CASE ug/l, As(V) 2.13 ug/l AUG-12: As(III) ug/l, As(V) 2.23 ug/l JUL-12: Total As 4 ug/l FEB-13: Total As 24.7 ug/l MAR-13: Total As 4.41 ug/l MAR-13: As(III) ug/l, As(V) 3.07 mg/l Raw after filters: FEB-13: Total As 2.6 ug/l MAR-13: Total As 2.86 ug/l MAR-13: As(III) 0.02 ug/l, As(V) 2.57 ug/l Final Blend 3:1: MAR-13: Total As 0.66 ug/l MAR-13: As(III) <0.01 ug/l, As(V) ug/l Raw at Wells: OCT-12: As(III) 16 ug/l, As(V) 2.45 ug/l RFP Sampling: April 2011: μg/l total As August 2011: 12 μg/l total As November 2011: μg/l total As NF Permeate: MAR-13: Total As 0.2 ug/l MAR-13: As(III) <0.01 ug/l, As(V) ug/l Piloting different NF membranes: 79 to 88% total As removal

27