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

Integrated Sustainability Consultants Ltd. is an employee-owned engineering and consulting company specializing in water and wastewater treatment, water management, waste management and energy solutions.

Contact Us: Emily Zevenhuizen Water/Wastewater Engineer, E.I.T. Applicant Integrated Sustainability Consultants Ltd. Telephone: (403) 390-6978 E: emily.zevenhuizen@integratedsustainability.ca

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