WATER | WASTE | ENERGY
Order of Discussion
1. Background 2. Membrane operation and fouling 3. Fouling mitigation and design of
membrane systems 4. Case study 5. Conclusion
What is Membrane Filtration?
Pressure-enhanced separation of solids
Types of Membrane Filtration
Required Pressure
Membrane Applications in Western Canada
• Oil and gas • Municipal and well water treatment • Other industries
Issues with Membrane Filtration
• Fouling potential • Feed-water requirements • Concentrate waste management • Energy consumption
Background – Fouling
Membrane Fouling • Results in clogging of the
membrane • Causes increase in pressure
or decrease in permeate flow
• Increases energy demand and decreases the membrane life
Background – Membrane Fouling
Virgin Membrane Fouled Membrane
• Reversible or irreversible • Due to operational parameters or constituents
within the feed water
Operational Parameters that Affect Fouling
• Membrane type • Permeate (critical) flux • Concentrate ratio • Cleaning and backwash
Fouling due to Feed Water Quality
• Colloidal • Organic
• Precipitive (metals or scaling)
• Biofouling
Background – Pre-treatment
Physical
• Low-pressure membranes (for NF/RO)
• Media Filtration • Settling
Chemical
• Coagulation • Disinfection • Oxidation • Water Softening
• Feed-water pre-treatment reduces fouling by improving the feed-water quality
• Several different types both physical and chemical
Criteria for Determining Pre-treatment
Determine pre-treatment to reduce NF fouling at potable water treatment plant Steps: 1. Characterize fouling 2. Determine pre-treatment requirements 3. Pre-treatment assessment (bench/pilot-
scale) 4. Full-scale application
Step 1: Characterize Fouling
Characterize your water source
Analyze membrane fouling
Perform membrane autopsy
Step 2: Determine Pre-treatment Requirements
• Based on your source water quality and plant set-up/space availability
Colloidal Precipitive Organic Biofouling
Total Suspended Solids (TSS)
Metals, Carbonates and/or Sulfates
DOC, TOC, SUVA, UV254
Bacteria, coliforms
Settling, filtration, floatation
Antiscalant, water softening, metal precipitation, Greensand filter
Coagulation, Carbon Filter, Ion exchange
UV or Ozone oxidation, or chemical oxidation
Step 3: Pre-treatment Assessment
• Bench/pilot-scale analyses under full-scale operating conditions
• Perform a trial under current conditions and pre-treatment condition(s)
Step 4: Full-scale Application Water Treatment Facility
Step 4: Full-scale Application Potable Water for 30-Person Camp
Pre-Treatment: • Chlorine addition • Preliminary filter • Sand filter • Activated carbon filter • Water softening system
Case Study
Case Study - Background
• Small municipal WTP • Lake source water • Integrated Membrane
System • High NF fouling rates • Small footprint
Case Study - Water Treatment Plant
High level of organics in source water NF feed-water meets recommended guidelines for high-pressure filtration (AWWA)
Case Study - System Mass Balance
Raw Water
TOC = 4.25 mg/L
MicroFiltration TOC = 4.10 mg/L
3.5% Removal
NanoFiltration TOC = 0.40 mg/L 90.6% Removal
90.6% reduction of TOC within system
Case Study - NF Membrane Operation
4
4.5
5
5.5
6
6.5
7
7.5
8
60
65
70
75
80
85
90
95
100
0 50 100 150 200
Flo
w (m
l/min
)
Fee
d P
ress
ure
(psi
)
Time (hrs)
Pressure
Flow
Case Study – Step 2: Determine Pre-treatment
Parameter Value (units)
TOC 4.1 - 5.7 (mg/L)
DOC 3.8 - 5.5 (mg/L)
UV254 0.163 - 0.211 (cm-1)
SUVA 3.84 - 4.40 (L/mg/cm)
Case Study - Process Diagram
Case Study - Mass Balance DOC Removal
0
10
20
30
40
50
60
70
80
90
100
No Coag. w MF FeCl3/MF PAX/MF Alum
Per
cen
t M
ass
of
Org
anic
s (
mg
of
C)
Pre-treatment Type
Remaining
NF Removal
Coag./MF Removal
Case Study - NF Feed Pressure
0
20
40
60
80
100
120
1 6 28 48 54 74 124 148 170 193 197.5
Fee
d P
ress
ure
(psi
)
Operation Time (hrs)
Non-coagulated
FeCl3
PAX
Alum
Case Study - Conclusion
• NF membrane had organic fouling • Fouling resulted in increased pressure
requirement and frequent backwashing and cleaning
• Pre-treatment with coagulation – Up to 50% of dissolved organic removal prior to NF
membrane
– Significantly reduced pressure requirement with coagulation
Overall Conclusion
• Pre-treatment can greatly improve membrane operation
• Pre-treatment is dependent on source water type, and membrane type
• Reduction of energy requirement, less damage to membrane
• Don’t get fouled up!
Acknowledgements
• Heather Daurie and Elliott Wright • Research group at Dalhousie University • NSERC / Halifax Water Research Chair
Program • Research Facilities provided by the
Institute for Research in Materials.
WATER | WASTE | ENERGY
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Contact Us: Emily Zevenhuizen Water/Wastewater Engineer, E.I.T. Applicant Integrated Sustainability Consultants Ltd. Telephone: (403) 390-6978 E: [email protected]
Types of Membrane Filtration
RO
Particles (>0.1µm)
Macro- Molecules (MW 2kD-500kD)
Molecules (MW 200D-2kD)
Ions
Pure Water
RO Reverse Osmosis
NF NanoFiltration
UF UltraFiltration
MF MicroFiltration
Case Study - Summary
• Optimal Coagulant Dose Selection – FeCl3- 0.5 mg/L of Fe @ pH = 5.0 – Alum- 0.6mg/L of Al @ pH = 5.5 – PACl- 1.15 mg/L of Al @ pH = 5.7
• Feed Pressure Averages: – Non-Coag./MF: 80.5 psi – FeCl3/MF: 64.1 psi – PACl/MF: 65.3 psi – Alum/MF: 69.7 psi
Case Study - Pre-treatment Assessment
• Removal of foulants • Effect on pressure • Effect on membrane operation
Operational Parameters that Affect Fouling
• Type of membrane (composition and permeability)
• Permeate (critical) flux • Waste efficiency (yield) • Cleaning and backwash
Outlet Concentrate Stream