Organic Contaminant Removal and Membrane Fouling

Transcription

1 Advanced Membrane Technologies Stanford University, May 07, 2008 Organic Contaminant Removal and Membrane Fouling Martin Reinhard Eva Steinle-Darling, Megan Plumlee, Federico Pacheco, Yi-li Lin Civil and Environmental Engineering Stanford University

2 Idealized membrane separation Steinle-Darling et al., Water Research, 2007

3 Solute-membrane-feedwater matrix interactions Rejection mechanisms Size exclusion Charge repulsion Solute - Structure - Molecular size/mass - Shape/diameter - Charge/pK a - Hydrophilicity Membrane -Type - Surface charge - Surface roughness - Cross-linking - Contact angle - Pore size/mwco - Performance indicator - Solute reactions Ionization Coiling Complexation Membrane modifications Charge neutralization Adsorption, fouling Feed water - ph, cations - Salt content - Foulants, bacteria - Organic matter - Hardness

4 Simplified solute-matrixmembrane interaction scheme Organic Compound MW < MWCO MW > MWCO ph < pka Neutral ph > pka ph < pka Neutral ph > pka Log K ow > 2 Log K ow < 2 Transmission Rejection Sorption + transmission Sorption + fouling

5 Rejection and fouling, formation of cake layer

6 Surface roughness virgin ESPA-3 SEM AFM Scale bar: 500 nm Surface roughness increases surface area and causes cavities both promote sorption.

7 Fouling processes Colloids, polymers, inorganic precipitates and bacteria form a cake at the membrane surface. Biofilm

8 Concentration polarization with permeable foulant layer D = alginate layer D inside fouling layer is same as D in water. Concentration at the membrane surface, Cm increases. Gradient driving diffusion increases Permeate concentration increases Steinle-Darling et al. Water Research. 41, (2007)

9 Investigative approach 1. Select test chemicals 2. Characterize membranes 3. Quantify solute rejection 4. Study solution conditions 5. Observe rejection in fouled membranes 6. Infer rejection mechanisms 7. Compare laboratory with treatment plant data

10 Test chemicals Nitrosamines O O OH Perfluorocompounds OH O O O OH THM precursors + tannic acid (MW 1700 Pharmaceuticals

11 Experimental approach 1. Adjust solution conditions and precompact membrane 2. Spike compound into feed tank. 3. Measure compound in feed, concentrate, and permeate, and membrane 4. Evaluate mass balance Steinle-Darling et al. Water Research. 41, (2007)

12 Nitrosamines Name NDMA NMEA NPyr NDEA NPip NDPA NPBA Structure MW LogK ow small hydrophilic uncharged NDMA 2 ng/l reporting limit

13 Nitrosodialkylamine rejection in DI water: MW dependence Flat-sheet cell data ESPA3 Steinle-Darling et al. Water Research. 41, (2007)

14 Artificially deposited alginate lowers rejection Steinle-Darling et al. Water Research. 41, (2007)

15 Rejection below MWCO varies with membrane type Low-fouling lower flux High flux

16 Transmission of Nitrosamines increases with salt passage LFC3 BW30 ESPA3

17 NDMA Removal at Interim Water Purification Facility 14% 0% 0% 33% 64% IWPF Orange County Water District 91% Plumlee et al. Water Research. 42, (2008)

18 NDMA removal by RO and UV Plumlee et al. Water Research. 42, (2008)

19 PFC compounds Perfluorooctanoic acid (PFOA) F F F F F F F O 1H,1H,2,H,2,H-perfluorooctane sulfonate 6:2 FtS F F F F F H H O F CO F SO F F F F F F F Perfluorooctane sulfonate (PFOS and C 4 to C 8 ) F F F F F F F F O F F F F F H H Perfluorooctane sulfonamide (FOSA) O O F SO F(CF 2 ) 8 SO-NH 2 F F F F F F F F O O MW range Da, surface active, all charged, except FOSA

20 Neutralization of membrane charge reduces rejection Cut-off shift

21 PFC rejection: size and charge O F(CF 2 ) 8 SO-NH 2 O Pentyl Tightness NF200>NF>270>DK>DL

22 Sorption dependence of PFCs and FOSA on NF270 FOSA (not charged) sorbs more than neg. charged analogues and is rejected less.

23 Approach to steady-state rejection of FOSA NF270

24 PFC: Salt and PFC Transmission looseness High jump in FOSA transmission is not accompanied by proportional increase PFC transmission

25 Polyphenols and hydroxy acids Phloroglucinol MW 126 Da Radius nm pk 1 = 8.0 Resorcinol MW 110 Da Radius nm pk 1 =9.4 3-Hydroxybenzoic acid MW 138 Da Radius pk 1 = 4.0 Tannic acid MW 1701 Da Radius nm Yi-Li Lin et al. J. Haz. Mat. 146, (2007)

26 O/N ratio, cross-linking and charge Cross-linking determines surface charge, polymer rigidity, and MWCO n = 1 Fully crosslinked Charge low O/N ratio = 1 n = 0 Linear Charge high O/N ratio = 2 NF NF XPS analysis: elemental composition in surface layer (1 to 5 nm)

27 NF70 and NF270 Properties 10 Property NF70 NF270 Type arom. semi-ar. 0 Zeta Potential (mv) NF270 NF70 Flux (70 psi) L h -1 m -2 O/N (cross-linking) CaCl 2 rejection % MWCO Pore radius Roughness (rms) nm Zeta potential at ph lower higher -40 ph Yi-Li Lin et al. J. Haz. Mat. 146, (2007)

28 Property Organic removal Type Flux Cross-linking CaCl 2 rejection MWCO Pore radius Roughness (rms) nm Zeta potential at ph 7 NF70 high arom. low high high low small high lower lower NF270 low semi-a high low low high high low higher higher Yi-Li Lin et al. J. Haz. Mat. 146, (2007)

29 Removal of pharmaceuticals and EDCs by NF Kimura et al. JMS

30 Removal of selected PhACs in pilot MF-RO system (μg/l) Compound Inf. MF RO % removal Ibuprofen OH-Ibuprof Gemfibrozil Naproxen HO- O OH OH O OH O O O Ibuprofen MW Gemfibrozil MW Naproxen MW 230.3

31 Summary and conclusions 1. The MWCO of a membrane depends on compound structure and solution properties (pka, solution ph). 2. The membrane type influences passage of small compounds. 3. Increasing ph increases rejection of acidic compounds; effect is stronger with the highly cross-linked membranes.

32 Summary and conclusions 4. Some trace organics sorb - uncharged solutes more than charged solutes. 5. Sorbing compounds are rejected less. 6. Fouling deepens polarization layer and decreases organics rejection. 7. Pharmaceuticals are removed by RO 70 to >99% NF 60 to 99%.