Micro- and ultrafiltration

Transcription

1 CT4471 Drinking water I Dr.ir. S.G.J. Heijman micro- and ultrafiltration Micro- and ultrafiltration

2 Application area filtration processes Size, µm Approximate moleculair weight Relative size of materials in water Viruses Bacteria Dissolved salt Algea Humic acids Cysts Sand Clay Silt ΔP [bar] Conventional filtration processes 0.01 Treatment process Ultrafiltration Nanofiltration Reverse osmosis ED and EDR Microfiltration Metal ions Arseen Nitraat Nitriet Cyanide Dissolved salt Calcium salts Sulphate salts Maganesium salts Aluminium salts Viruses Hepatitis Humic acids Trihalomethanen Precursors Bacteria Salmonella Shigella Vibrio cholerae Cysten Protozoa Giardia Cryptosporidium October 16,

3 Application area filtration processes Bacteria Virusses Multivalent salts Monovalent salts Microfiltration MF Ultrafiltration UF Nanofiltration NF Reversed Osmosis RO October 16,

4 Why MF/UF? Removal of bacteria and virusses is expressed as logremoval capacity 90%-removal = log 1 99%-removal = log 2 99,99%-removal = log 4 suspended solids organische subst. Giardia Cryptosporidium MS2-virus microfiltration 99% 50% > 4 > 4 0 ultrafiltration 99% 50% > 4 > Introduction

5 Full scale 1. Introdcution

6 Module A spec A = I mem module n π d L = 1 2 π D 4 A spec = specific membrane surface [m 2 /m 3 ] A mem = membrane surface area [m 2 ] I module = module volume [m 3 ] N = number membranes in module [-] d L D = diameter membrane [m] = length membrane [m] = diameter module [m] 2. Concept MF/UF

7 Dead-end Filtration filtration backwash or backflush 2. Concept MF/UF

8 Mass balans Filtration time Q f Q p = Q f Q p Filtration run = filtration time + back wash time Q f =Q p+ Q bw Q p = permeate flow [m 3 /h] Q f Q bw = feed flow [m 3 /h] = back wash flow [m 3 /h] 3. Theory October 16,

9 Recovery γ = V V p V p r γ = recovery [-] V p = permeate production [m 3 ] V r = volume needed for cleaning [m 3 ] Recovery as high as possible (>90%): - long filtration time - short cleaning time - low cleaning flux 3. Theory October 16,

10 Kinetics J = A Q p mem TMP = ν R tot J = flux [m 3 /(m 2 h)] Q p = permeate flow [m 3 /h] A mem = membrane surface area [m 2 ] TMP = transmembrane pessure [Pa] R tot = totale resistance ν = dynamic viscosity [Pa/s] R tot =R membrane +R fouling resistance flux time 3. Theory October 16,

11 Fouling mechanisms 3. Theory October 16,

12 Trans membrane pressure P feed P Conc TMP ΔP P Perm hydr = PFeed P ΔP Hydr 0 perm 2 P Perm 0 3. Theory October 16,

13 Cleaning Different cleaning methods: - forward flush or cross flow - backflush or backwash - Airflush or air/water flush - Chemical enhanced flush or chemical backwash - intensive chemical cleaning or cleaning-in-place (CIP) 3. Theory October 16,

14 Forward flush Feed Flush water Cleaning with high cross flow velocities Re > 2300 Re = v o d h ν Need cross flow for turbulent conditions d [mm] v o [m/s] drukval [Pa] 5,2 0, ,5 2, ,7 4, Theory October 16,

15 Back flush Backwash water permeate Backwash flux = 2 tot 2,5 filtration flux Time needed to flush a membrane of 1 meter with a backwash flux of 250 l/(m 2 h) d [mm] flush time [s] 5,2 19 1,5 5 0,7 3 October 16, Theory

16 Back flush with forward flush October 16,

17 Air flush Forward flush with air injection higher turbulence air Taylor bubbles Slug flow 3. Theory October 16, Water

18 Design concepts Different modules: - tubular membranes - capillary membranes 1. flat sheet membranes Different operational modes: - dead end - cross flow - under pressure - constant pressure - constant flux Different orientation: - vertical - horizontal Different materials: - polymer - ceramic 4. Design concepts October 16,

19 Tubular membranes Diameter channel = 5 25 mm Easily cleaned Low specific surface area Low clogging potential 4. Design concepts October 16,

20 Capillary membranes Diameter channel = mm Well cleaned, but not as good as tubular membranes High specific surface area High clogging potential 4. Design concepts October 16,

21 Choosing a module Economical balance: low investment costs vs low exploitation costs or high specific surface area vs low clogging potential High flux >>> fast fouling 4. Design concepts October 16,

22 4. Design concepts Vertical - horizontal

23 P v, F w P v, F w ± 20 min constant pressure (ca 0.5 bar) backwash constant flux (ca 100 l/m 2 h) time time flux pressure flux pressure October 16, Design concepts

24 Dead-end vs Cross-flow filtration Q f Q p Q c Q v CF: Application with high suspended solid contents Q p CF: High cross flow velocities, high energy costs 4. Design concepts

25 Under pressure membrane filtration Feed water concentrate membranes permeate air 4. Design concepts

26 Ceramic microfiltration October 16,

27 Ceramic microfiltration Membrane layer October 16,