Berrigan- Nitrate-Removal_April-7-2016-Minnesota-AWWA-Metro-District

Nitrate Removal TechnologiesAlternatives and Costs

John K. Berrigan Jr., PEManager Water/Wastewater

April 6, 2016

Nitrate Removal Technologies

• Alternatives

• Ion Exchange

• Reverse Osmosis

• Electrodialysis

• Biological treatment

• Nontreatment alternatives

• Conclusion

AlternativesBest Available Technologies

Alternatives

• Best Available Technologies

– Ion Exchange

– Reverse Osmosis

– Electrodialysis

• Additional Technologies

– Biological Treatment

Ion ExchangeBest Available Technology

Ion exchange

• A process in

which ions are

exchanged

between a

solution and an

insoluble solid.

McCook NE, two-stage ion exchange removal

Courtesy Tonka Water

Ion Exchange Applications

• Calcium

• Magnesium

• Radium

• Nitrate

• Arsenic

• Uranium

• TOC

Ion Exchange Selectivity

• Cation (positive) exchange selectivity:

Fe3+ > Ra2+ > Fe2+ > Mn2+ > Ca2+ > Mg2+ > Na+

• Anion (negative) exchange selectivity:

U > DOC > SO42- > NO3

- > As5- > Cl- > HCO3-

Ion Exchange Resin

Courtesy Thermax

Ideal Resins for Nitrate Removal

• Macroporous (large pore size)

• Strong base anion exchange resin

• Certified to the ASTM/NSF 61 standard

• Nitrate selectivity

• Examples

– Purolite 520E @ $310/cubic foot.

– Thermax A-62 MP @ $240/cubic

Macroporous Ion Exchange Bead

Courtesy Dow Chemical

Ion Exchange Beads

Courtesy Dow Chemical

Ion Exchange Vessel

• Distributor

• Collector

• Brine System

• Shell

Courtesy Tonka Water

Ion Exchange Process

• Service Mode

• Regeneration Mode

– Backwash

– Brine

– Slow Rinse

– Fast Rinse

Resin Regeneration - Brining

Background photo courtesy Dow

Service

• Each vessel operates for a pre-determined amount of

water

• Determined by batched effluent meter

In Service Mode

Background photo courtesy Dow

Backwash

• Up-flow

• Expands resin bed and removes accumulated

solids

• Breaks up any bridging of resin

• “Fluffs” resin exposing new sites for ion exchange

• 100% feed water

• Can be recycled/reclaimed

Brine/Slow Rinse

• Brine

– Replenishes exchange sites with Cl-

– Drives out adsorbed organics

• Slow Rinse

– 100% treated water

– Brine moves evenly out of the bed

– Maintains slow brine rate

Brine

Background photo courtesy Dow

Fast Rinse/Return to Service

• Washes away residual salinity

• 100% feed water

• Return to service at conductivity setpoint

Ion Exchange Process

• Service Mode

– Each vessel operates for predetermined amount of

water treated (typically 1,000 – 1,500 gallons/cubic ft.

of resin).

– Nitrate exchanged for chloride ions on the resin

• Regeneration Mode

– Accumulated nitrates are removed

– Resin bed is rejuvenated

– Approximately 80-100 minutes

Ion Exchange Process

• Nitrate Specific Requirements

– Regeneration is counter-current

– Two stages if nitrates are above MCL

Case Study - Hastings

Courtesy City of Hastings, MN

Representative Costs

• Facility cost – $3.5 Million (~5.0 million in 2016 $)

• Capacity – 2,400 gpm (blended flow)

• Resin capacity 160# of nitrate (as N)

• 4 Vessels able to treat >500,000 gal

• Regeneration requires 1.0-1.5 tons of salt.

• Salt is generally $150-$200/ton $0.40/1,000 gal.

• Blending reduces cost

Equipment

• Ion exchange system

– Vessels

– Resin

– Salt storage, brine pumping

– Valves, actuators, compressor

– Instruments and controls

• Chemical feed

• Pumping equipment

• Building and property

Courtesy City of Hastings, MN

Reverse OsmosisBest Available Technologies

RO – Membrane Introduction

• Membrane - a thin piece of material that has no

visible holes.

• From the Latin “membrana”, meaning “skin”.

• Examples

– Roofing membranes

– Reverse osmosis membranes

– Cell membranes

RO – Membrane Introduction

Every operator has a working knowledge of at least five membrane systems operating in this room:

• Blood vessels

• Kidneys

• Lungs

• Stomach

• Skin

RO – Membrane Introduction

Circulatory System is a complex membrane filtration

system.

• Blood vessels, arteries, veins, capillaries

• Red blood cells, platelets, white blood cells

• Plasma

• Valves (heart, veins)

• Pumps (heart)

Photo courtesy of Medtronic®

RO – Membrane Introduction

Kidneys are a membrane

separation system

(micro & nanofiltration)

• Selective separation of

nitrogen compounds

• Foundation for treatment

for nitrates

Photos courtesy of Medivators®

RO – Membrane Introduction

• Filtration of Particles

– Microfiltration (MF)

– Ultrafiltration (UF)

• Selective Separation of Solubles

– Nanofiltration (NF)

– Reverse Osmosis (RO)

RO – Membrane Introduction

Photo Courtesy of GE

RO – Membrane Introduction

Courtesy Osmonics

RO – Membrane Introduction

• Feed = The water pumped into the membrane

system, after pretreatment.

Feed Permeate

Concentrate

Membrane

RO – Membrane Introduction

• Permeate = The portion of the feed which passes

through a membrane.

Feed Permeate

Concentrate

Membrane

RO – Membrane Introduction

• Concentrate = The portion of the feed which does

not pass through a membrane.

Feed Permeate

Concentrate

Membrane

Operating Fundamentals

• Recovery = The proportion of the feed which passes

through a membrane.

• Recovery = QPermeate/QFeed

Feed Permeate

Concentrate

Membrane

QFeed QPermeate

Operating Fundamentals

• Rejection = The proportion of a contaminant

retained by a membrane.

• Rejection = CConcentrate/CFeed

Feed Permeate

Concentrate

Membrane

CFeed

CConcentrate

RO – Membrane Introduction

• TMP = Transmembrane pressure, the pressure

differential across a membrane.

• TMP = PFeed - PPermeate

Feed Permeate

Concentrate

Membrane

PFeed PPermeate

RO – Membrane Introduction

• Flux = Flowrate of the permeate through a

specific unit area of membrane.

• Flux = J = Qpermeate/AMembrane

Feed

Concentrate

Membrane

PermeateAMembrane

QPermeate

RO – Membrane Introduction

• Flux – rate of flow per unit membrane area (similar to

filtration rate).

• Transmembrane pressure – feed pressure minus permeate

pressure (direct mode) (analogous to filter head loss).

• Rejection – percent of contaminant excluded.

• Recovery – percent of feed flow produced by the system.

High Pressure Pump

Permeate

Concentrate

Recycle

(if necessary)

Control Valve

Feed

RO –Process

RO – Capital Cost Components

• Power (Pumping against 60 Δpsi - 90 Δpsi)

• Pretreatment Chemicals (acid and antiscalents)

• Prefiltration materials (1μ - 5μ cartridge filters)

• Membrane replacement @$300 - $500/cartridge

• Concentrate disposal

– May be technically infeasible

– May influence the cost of treatment by limiting recovery.

– Within separate sanitary districts, often cost prohibitive.

RO – Operating Components

• Power (antiscalent, preoxidation)

• Prefiltration (5μ)

• Pumps (60 Δpsi - 90 Δpsi)

• Membrane Skids (assemblies of cartridges)

• Cleaning and flushing systems

• Post-treatment equipment (Cl2, CO2 etc.)

• High service pumps

Case Studies – Cross City, FL

• Pretreatment

– Iron

– Manganese

• RO

– TOC

– Nitrate

– Hardness

Case Studies – Cross City, FL

• 2 mgd plant

• $3,500,000

• Gravity filters

• RO Trains

• Chemical feed

• Controls

Photo courtesy of WPC Contractors

Case Studies – Cross City, FL

• $3,000,000

• Concentrate

blended with

WWTP effluent

• Pumps

• 2 mile pipeline

• Spray field

• Controls

Photo courtesy of Wet Engineering

Case Studies – Council Bluffs, IA

Map Courtesy Google

Case Studies – Council Bluffs, IA

Capital Cost 5 10 20 PW

($ millions) mgd mgd mgd

Lime Softening 28.6 31.7 48.7 126

UF/RO 22.7* 28.5 42.4 106

• UF/RO pilot on the Missouri River source water

• Source water from collector wells under the river bed.

• Pilot report submitted to Iowa DNR for approval

• Based on pilot results, the UF/RO facility constructed.

* Estimated and actual construction costs the same. Cost estimates developed independently by HDR

Case Studies – Council Bluffs, IA

Operating Cost 5 10 20 PW

($ millions) mgd mgd mgd

Lime Softening 2.1 3.6 6.8 126

UF/RO 1.5 2.7 5.4 106

• Difference in operating costs influenced heavily by

solid waste handling and disposal.

Cost estimates developed independently by HDR

ElectrodialysisBest Available Technologies (Iowa, California)

Electrodialysis Reversal

• Uses electric field to reduce ion content

• Recoveries of 85%-95%

• Less sensitive to turbidity than RO or ion exchange

• Roughly 10 plants in Iowa

Diagram Courtesy GE

Electrodialysis Reversal

• Washington, IA

• Installed 1997

• Fairfield, IA

• Installed 2003

• Capital costs similar to RO

• Disposal options are a

deciding factor

Photos Courtesy GE

Biological TreatmentAvailable soon?

Non-treatment Alternatives

Nontreatment alternatives

• Drill a new well

• Connect to another utility

Nitrate Removal Technologies

• Alternatives

• Ion Exchange

• Reverse Osmosis

• Electrodialysis

• Biological treatment

• Nontreatment alternatives

• Conclusion

Thank you!