Low Pressure Membrane Filtration System Operations

Nick LucasMISCO Water

New Mexico PWO Seminar

Agenda

Membrane Basics

Comparison to Conventional Treatment Systems

Drivers & Applications

Operations Discussion

Low Pressure Membrane Filtration Basics Membrane filtration is a pressure-driven separation

process through semi-permeable membrane material with a pore size of less than 1 µm

Typically hollow fiber membrane

Outside-in flow pattern most common

Membranes Provide Physical Barrier

Filtrate

Cross-section: dirty fiber

Dirt on Fiber SurfaceDiatom on Fiber SurfaceCrypto on Fiber Surface

Membranes provide physical barrier against:

•Suspended solids•Cryptosporidium•Giardia•Bacteria•Colloids•Viruses

Does NOT affect:•pH/conductivity•Dissolved solids

Typical Water/Solids Separation Processes

Comparison: Conventional & Membranes Conventional

Technologies:

Clarifiers & Media Filters

Chemically assisted separation

Sensitive to feed water changes

Sensitive to flow changes

Treated quality subject to breakthrough

Minimal temp effects – media filters

Large temp effects - clarifiers

Treatment Mechanisms Differ Conventional

Technologies:

Clarifiers & Media Filters

Chemically assisted separation

Sensitive to feed water changes

Sensitive to flow changes

Treated quality subject to upsets

Minimal temperature effects

Membrane Filtration:

Physical separation

Copes with sudden, short-term feed condition changes

Copes with sudden flow changes

Stable treated water quality

Temperature impacts to production performance

Low Pressure Membrane Drivers/Applications Drivers

Surface Water Source – treatment removal credit Need/Desire for High Effluent Quality Verifiable Pathogen Removal Footprint Considerations High Recovery Requirements Simplicity of Operations – High Degree of Automation Flexibility of Operations – Start/Stop Ability

Applications Surface Water Treatment (multi-process component or direct feed) Groundwater (GUI) Reuse applications Pretreatment to NF/RO

Pressure & Submerged Low Pressure Membrane Systems

Pressurized: Membrane modules operate in a closed environment. Feed water is pressurized (pump or gravity) through the modules and membrane skid or unit. The modular skid design simplifies installation and operation.

Submerged: Membrane modules operate in a open tank, or cell. This configuration allows for visual inspection, simple membrane installation and removal. Feed water enters the cell by gravity and a suction pump draws water through the immersed membrane modules.

Wide Range of Flow Applications Small Package Systems

Large Component Systems

Air System

H

CIP System

PLC&I/O

..O

..O

..O

..O

..O

..O

..O

..O

..O

..O

..O

..O

Membrane System

VV

VFeed

HMIMaster PLCSCADA

Strainer Feed Pumps

Compressors/Blowers

HeaterTankRecirculation Pumps

MembranesHousingsFrame/cells PipingValvesInstrumentsPLC Scope of Supply

Typical Membrane System Scope of Supply

General Membrane Modes of Operation

Normal Filtration

Backwash

Chemical Cleaning

Integrity Testing

Filtrate

Normal Filtration CycleFeed stream

StartFiltration

Feed stream

Filtrate

EndFiltration

Raw water is pressurized or drawn to the membrane fibers

Particles larger than pore size remain on surface

Filtrate, is collected in the inside (lumen) of the fibers

Water from the fiber bundles (modules) is collected and sent to the next process in the application train

Raw/Feed Water

Filtrate

DefinitionsFouling – gradual accumulation of contaminants on a membrane surface

or within a porous membrane structure that inhibits the passage of water

TMP – Transmembrane Pressure – pressure drop across membrane fiber –measure of membrane fouling/performance

Flux – throughput of a pressure driven membrane filtration expressed as flow per unit of membrane area [gal/ft2*d] – way of measuring how hard a system is being run

Permeability – ability of a membrane barrier to allow fluid passage as flow per unit of membrane area [gal/ft2*d*psi]

Air Scour Backwash Cycle Primary solids removal mechanism Fully automated process Based on time or volume

Chemical Cleaning

Chemical/Physical method of fouling control Frequency dependent on flux and backwash interval

Common chemicals Sodium Hypochlorite and/or Sodium Hydroxide (or blend) Citric, Sulfuric, Phosphoric or Hydrochloric Acid (or blends)

Steps include Filtrate recirculation / Soak / Aeration

Maintenance Washes: Typically 45 minute duration / lower chemical concentration / unheated

Frequency varies depending on application (daily to weekly per unit)

Clean In Place (CIP): Typically once per month / heated

Usually “dual” cleans; 2-3 hours per chemical

Integrity Testing Verifies intact barrier

Fibers

Orings

Seals

Is more sensitive than particle counters and turbidimeters

Can be correlated to a Log Removal Value (LRV) for pathogens 0.3 micron (or greater) per EPA Membrane Filtration Guidance Manual

Integrity Testing – How it Works

Apply Air

Flaw time

P

Decay Rate Low

Decay Rate High

Integrity Recovery via Bubble Test & Pin Repair

‘Squirter’ Identified

Pin Repair is Permanent

Low pressure air applied to leaking module without removal from skid

It’s All in the Details

Stable, LowCost, Long TermPerformance

FeedConditions

Long TermFouling

PlantSizing

Conc.Coagulant

ChlorineConstantTrace

SpikesSeasonal

Trials

Bench-marking

CleaningInterval

Recovery

B/washEfficiency

TMP

CleaningEfficiency

Integrity

Operation

Flexibility

ControlMethodology

Regular Maintenance

Cleaning Schedule

Trend Monitoring

Integrity Mgmt

Low Pressure Membrane Systems:Shift in Focus from Conventional Treatment

CONVENTIONAL MEMBRANE

Chemical Optimization enhances separation and effluent quality

Incoming Feed Changes Can Adversely Impact Effluent Quality

Steady state Operation Yields Best Performance

Temperature Not Large Impact on Filter Media Performance – more impact on Clarification processes

Effluent Largely a Given – focus on monitoring membrane performance

Incoming Feed Changes Can Adversely Impact Effluent Quantity

Flexibility in Operations through Start/Stop Ability – ability to cycle units in and out of service quickly

Temperature (via viscosity) has large impacts on throughput and level of performance (i.e. permeability, flux)

Operations Focus ItemsFOCUS ITEM RESULTING GENERAL APPROACH

Effluent Largely a Given – focus on monitoring membrane performance

Incoming Feed Changes Can Adversely Impact Effluent Quantity

Flexibility in Operations through Start/Stop Ability – ability to cycle units in and out of service quickly

Temperature (via viscosity) has large impacts on throughput and level of performance (i.e. permeability, flux)

Focus on Performance Trends and Cleaning Intervals – Data Collection/Monitoring

Flexible Use of Backwash and Chemical Cleaning during Challenging Feed Periods

Alternate use of units during lower flow periods (shared burden) – Automated rotation to reduce downtime, up efficiency

Operational plans for colder temperatures when lower throughput expected ---generally coincides with lower demand

Data Monitoring – generic trend

Operating Time

2

4

6

8

10

12

14

16

18

TM

P (p

si)

CIP

Main

ten

an

ce

Wash

Trend Comparison

System Flux Selection & Operation Impact of operation at extremes not understood

Leaves little room for unexpected conditions

Requires frequent use of chemicals More frequent waste handling

Long term fouling in this mode is not fully understood

Increases operating costs

Greater energy usage

Greater chemical usage

Consider Impact on Eventual Membrane Replacement

More susceptible to viscosity effects

Operations Standpoint: High flux reduces operational time to meet short-term demand or increases capacity of current infrastructure (i.e. fill short-term gap)

adds long term risk –more fouling more chemical &More long-term residual fouling

More rapid membrane decline Less room for unexpected conditions & membrane replacement cost sooner

Flux & Temperature Impact on Performance

Membrane System Control System Membrane Control System and HMI/SCADA provides broad oversight

Active Warning and Shut Down Alarms

HMI Screens Displaying All System Component Operations

Data Monitoring & Logging Capabilities

Remote Accessibility

Membrane system often one component of broader architecture

Feed Pumps

StrainersMembrane

UnitsFeed tanks

Pre-treatment

Filtrate Tanks

Post-treatment

CIP EquipCompressed

AirBulk

Chemicals

Membrane Controller

System

Low Pressure Membrane System Maintenance Schedule

Regular Maintenance – Membrane Maintain Chemical Cleaning Interval Integrity Monitoring (Sonic Test Mapping)

Regular Maintenance – Ancillary Equipment Valve actuator timing/seating Instrumentation Calibration Compressor/Blower (oil filter change) Strainer cleaning Dosing Pump Calibration

Long-Term Maintenance Rotating Equipment (pumps, compressors, blowers, etc.) Membrane Repairs O-ring replacements and seals

Long Term Equipment Care Membrane Replacement

$64,000 Question ---- How long will my membranes last????

Followed By Ultimate Sales Response ---- It depends

Factors: Flux, Operational Load, Feed WQ, Chemical Cleaning Regime, Preventative Maintenance Program, Pretreatment Process/Chemistry, Cost/Benefit Evaluation at End of Membrane Life

Major Rotating Equipment Feed Pumps, Compressors, Blowers

Skids Generally Planned for 30 year wear life Under right maintenance program maybe longer

First generation of large scale membrane systems entering third decade of service

Repairs/Rehabs can involve proprietary parts, but can add an extra 5-10 years to a long-term piece of equipment

Conclusions Paradigm Shift in Operator Focus from Conventional to Membrane Systems

Importance of Data Trend Analysis – Assessing Long-Term Performance

Trade-Offs in Operation (Short Term Benefits vs. Long Term Risks)

Various Controls System Oversight Options

Short Term Maintenance Requirements Membrane Maintenance

Regular Mechanical Ancillary Equipment Upkeep

Long Term Maintenance Requirements Integrity Management

Rotating Equipment Upkeep

Long Term Use Equipment Upkeep

Thank You for you Attention

Questions ?????

Nick Lucas