A REVIEW OF ARSENIC REMOVAL TECHNOLOGIES AND TECHNOLOGY SELECTION APPROACH

ZAID CHOWDHURY, PHD, PE, BCEE

SOUTHWEST AWWA CONFERENCEOCTOBER 16, 2017

Arsenic

• Current MCL 10 ug/L

• EPA is revisiting health effects data

• Next 6-yr Review?

• MCL may be lowered

History of regulatory development and research to assist affected utilities

• USEPA’s Arsenic Technology and Cost document

• AWWA’s national compliance cost estimate

• WRF projects:• Interactive Decision and Costing Tool

• Innovative technology research

• Technology Demonstration

• Secondary Impacts of As Rule

• National Drinking Water Advisory Council’s (NDWAC) committee to evaluate regulatory costs

Some basic facts about arsenic

• Arsenic naturally occurs in two forms:• Organic (seafood)

• Inorganic (water)

• Inorganic arsenic is more toxic than organic arsenic

• Inorganic arsenic occurs in two forms• Arsenite, As(III)

• Arsenate, As(V)

• As (III) is more toxic than As(V)

Health effects of arsenic

• Arsenic causes cancer of • Skin

• Bladder

• Lung and

• Prostrate

• Arsenic is also implicated in cardiovascular disease, diabetes and reproductive disorders

• Health effects research points to very low safe level

Arsenic occurrence in the US

Arsenic Rule impact

Arsenic Standard

Number of Systems Impacted

National Compliance Costs

EPA AWWA

3 µg/L 14,500 $7 Billion $28 Billion

5 µg/L 9,000 $4 Billion $14 Billion

10 µg/L 4,000 $2 Billion $5.5 Billion

20 µg/L 1,600 $0.6 Billion $1.5 Billion

• ~97% of impacted systems serve less than 10,000 people

• Small systems cost: $3-$30 per month per household

• Large system cost: $2-$4 per month per household

Technologies for arsenic removal

• Adsorption; GFH, GFO, ArsenX, AA, etc.

• Coagulation/Filtration or Coagulation/MF (softening)

• Ion Exchange

• Membranes (NF, RO, or EDR)

Most of these technologies can achieve >90 %

removal when optimized

Adsorption

• Adsorption capacity varies with media type

• Media performance is site specific and varies with:• pH

• Concentrations

• Competing ions

• Spent media must be removed and replaced

Spent Backwash

Treated Water

Backwash

Media

Raw Water

Adsor

bent

As(V)

W

A

T

E

R

Coagulation/Filtration

• Arsenic is removed by incorporation into flocs or adsorption on to flocs

• Flocs are removed by filtration or micro/ultra filtration

• Solids contain majority of arsenic and disposed as non-hazardous waste

Coagulant + Water = Flocs

As(V)

Ion Exchange

• Lower arsenic capacity compared to adsorption media

• Requires frequent regeneration cycles

• Sulfate interferes

• Spent regenerant may be hazardous

• Brine recycle increases the utilization of regenerant

• Treatment for regenerant is possible leading to the formation of a solid waste containing arsenic

Membranes

• RO/NF achieves high degree of removal

• EDR is partially effective

• Generates concentrated brine

Treatment interferences

• Adsorption:• Phosphate interferes with adsorption

• Coagulation:• Silica interferes with coagulation

• Ion Exchange: • High sulfate limits the use of ion exchange

• Nitrate and selenium peaking may occur

• Membranes: • High TDS may be problematic for membrane applications

Technology applicability for arsenic removal

TechnologyGW System

Applicability

SW System

Applicability

Prone to

Interferences

Need Sewer

Connection

Adsorption ✔️ ? Low No

Anion Exchange ✔️ ? High Yes

Coagulation ✖️ ✔️ Moderate No

Lime Softening ✖️ ✔️ Moderate No

Membranes ✔️ ✔️ Moderate Yes

Capital cost for arsenic removal technologies

$-

$2,000

$4,000

$6,000

$8,000

$10,000

$12,000

$14,000

0.27 1.2 7

Design Flow (mgd)

Ca

pit

al

Co

st

(in

$1

,00

0s

)

IX, at 20 mg/L influent SO4

IX, at 50 mg/L influent SO4

GFH, ambient pH = 7.5, 75,000 BVs

AA, ambient pH = 7-8, 10,000 BVs

AA, ambient pH = 8-8.3, 5,200 BVs

GFH, adjusted pH = 6.5, 110,000 BVs

AA, adjusted pH = 6.5, 23,100 BVs

AA, adjusted pH = 6.5, 15,400 BVs

CMF (w/o Sedimentation Basin)

Total cost for arsenic removal technologies

$-

$1.00

$2.00

$3.00

$4.00

$5.00

$6.00

$7.00

$8.00

$9.00

$10.00

0.27 1.2 7

Design Flow (mgd)

To

tal

Co

st

(in

$/k

ga

l)

IX, at 20 mg/L influent SO4

IX, at 50 mg/L influent SO4

GFH, ambient pH = 7.5, 75,000 BVs

AA, ambient pH = 7-8, 10,000 BVs

AA, ambient pH = 8-8.3, 5,200 BVs

GFH, adjusted pH = 6.5, 110,000 BVs

AA, adjusted pH = 6.5, 23,100 BVs

AA, adjusted pH = 6.5, 15,400 BVs

CMF (w/o Sedimentation Basin)

Some actual capital cost numbers from utilities in Arizona

Capital Cost

Treatment unit Flow Total Cost Unit Cost

Arizona Installations GPM $/gpd

granular iron media 900 $ 959,000 $ 0.74

granular iron media 1,100 $ 1,346,879 $ 0.85

granular ferric oxide 1,900 $ 2,202,383 $ 0.80

iron-enhanced media 725 $ 1,600,000 $ 1.53

granular ferric hydroxide at 3 facilities 3,900 $ 4,000,000 $ 0.71

granular ferric hydroxide at 2 facilities 3,100 $ 3,900,000 $ 0.87

granular ferric hydroxide 3,685 $ 2,500,000 $ 0.47

granular ferric hydroxide 4,097 $ 1,000,000 $ 0.17

granular ferric hydroxide 7,777 $ 1,500,000 $ 0.13

Average $ 0.70

TECHNOLOGY SELECTION APPROACH

Technology selection guidance available from published literature reports

Te

ch

nolo

gy s

ele

cti

on

d

ecis

ion

tre

e

Red flags for technology selection

Sulfate > 50 mg/L or Nitrate > 5 mg/L

Discharge of liquid residual to sewer or evaporation pond not available

High pH, well-buffered source-water

Ion Exchange

Regenerable Adsorbents

Ion Exchange

Membranes

Adsorbents

Coagulation/Filtration

Membrane

Technology selection drivers

$Operational

Complexity

Water

quality and

interfering

ions

Pilot testing leads the way to the most effective treatment system design

Figure 1. Adsorption Test

SkidFigure 2. Adsorption Test Skid

0.000

0.005

0.010

0.015

0.020

0 20,000 40,000 60,000 80,000 100,000

Bed Volumes Processed

Ars

en

ic C

on

cen

trati

on

(m

g/L

)

GFH Effluent

Raw Water or Influent

MCL

24,000 BVs

At 96,000 BVs

As is 9.4 µg/L

Operate small-scale column to determine arsenic

break-through profile

Design considerations

Take-away points

Water quality and operational

constraints – driver for technology

No arsenic level is safe – get to the

lowest feasible level

MCL may be lowered – be ready

Pro-active planning – saves money