Sub-Project A2: Simultaneous Removal of Inorganic Contaminants, DBP

Precursors, and Particles in Alum and Ferric Coagulation

The University of Texas at Austin Desmond Lawler, Lynn Katz

Isabella Gee, Seulki Yeo and Jon Herrboldt March 21, 2016

Introduction • Brief Description: Use enhanced alum or ferric coagulation for simultaneous inorganic

and natural organic matter removal, and develop a mechanistic understanding of the interrelationships between NOM, inorganic contaminants, and metal precipitation. Inorganic contaminants of interest include:

– Fluoride – Arsenic – Chromium – Manganese

• Anticipated target utility characteristics: - Small water systems using surface waters with elevated inorganic contaminant concentrations that may already be applying alum or ferric coagulation as part of their treatment process • Continuum of technology development:

Outputs and Outreach Completed: - “Mechanisms of fluoride removal: adsorption and co-precipitation with

aluminum hydroxide in the presence and absence of NOM” ACS National Meeting, Denver, March 2015

- “Impact of ligands on co-precipitation and adsorption with aluminum” ACS National Meeting, Boston, March 2016

Scheduled: none Anticipated: White paper for WINSSS website, late Spring 2016. Manuscript for submission to a technical Journal, Fall 2016. WINSSS or US EPA Small Systems Webinar – late 2016 or 2017

Outline

• Alum Coagulation for Fluoride Removal (Isabella Gee) – Bench- Scale Testing

• Synthetic Water • Natural Water

– Pilot Study Testing • MacKenzie Lake, TX • Manitou Springs, CO

• Fe Coagulation for Fluoride Removal (Ki Yeo) – Bench- Scale Testing

• Synthetic Water • Al and Fe Coagulation for Trace Metal Removal (Lynn Katz)

Synthetic Water Tests

Synthetic Water Test Conditions

Three NOM surrogates Pthallic Acid Pyromellitic Acid Salycylic Acid

pH varied Between 4 and 9

Coagulant dose varied Between 20 – 500mg/L

Reagent Quantity Unit Purpose

CaCl2 336 mg Hardness

NaHCO3 504 mg Alkalinity

NaCl Variable mg Ionic Strength

HCl (1N) 6 mL Acidification

H2O 1.994 L Background

Removal of Fluoride & Organic Acids

0

20

40

60

80

100

20 100 200

Fluoride OnlyPhthalic Acid and FluoridePyromellitic Acid and Fluoride

Fluo

ride

Rem

oval

(%)

Alum Dose (mg/L)

0

20

40

60

80

100

20 100 200

Phthalic AcidPyromellitic AcidPhthalic Acid and FluoridePyromellitic Acid and Fluoride

Org

anic

s R

emov

al (%

)

Alum Dose (mg/L)

Aluminum Residuals

SMCL

Natural Water Tests

Natural Water Tests

• Two Waters – MacKenzie Lake, TX – Manitou Springs, CO

• pH controlled

– pH 6.5 – Using Na2CO3, NaOH, and

HCl

• Alum dose varied between each jar – Between 20 – 500mg/L

Natural Water Characteristics

Parameter Natural Waters

TX Water Site

CO Water Site

Water Source SW SW pH 8.60 7.58 [F] (mg/L) 3.04 3.15 DOC (mg/L Carbon) 9.20 1.18 SUVA (L/mg-m) 0.87 1.76 Alkalinity (mg/L CaCO3) 294.6 16.8

Natural Waters from TX and CO - Fluoride and Organic Removal

4/5/2016 12

0

20

40

60

80

100

0 100 200 300 400 500

MMWA, TX pH 6.0MMWA, TX pH 6.5MS, CO pH 6.0MS, CO pH 6.5

Fluo

ride

Rem

oval

(%)

Alum Dose (mg/L)

TX: [F]i = 3.04 mg/L

CO: [F]i = 2.81 mg/L

0

20

40

60

80

100

0 100 200 300 400 500

MMWA, TX pH 6.0MMWA, TX pH 6.5MS, CO pH 6.0MS, CO pH 6.5

Org

anic

UV

-254

nm

Rem

oval

(%)

Alum Dose (mg/L)

TX: [Absorbance]i = 0.080 cm-1

CO: [Absorbance]i = 0.012 cm-1

Aluminum Residuals

SMCL

Pilot Studies

Pilot Studies

MacKenzie Lake, TX – pH varied with alum dose (High Alk water) – Alum dose varied between 100—300 mg/L

Manitou Springs, CO

– pH control required for low Alk water (6.5,7.5) – Alum dose varied between 20 – 300 mg/L

MacKenzie Lake, TX

TX Pilot Studies: Approach to Steady State

0

1

2

3

4

0 60 120 180 240 300

Fluo

ride

Con

c. (m

g/L)

Time (min)

Influent = 3.48 mg/L

Floc.

Sed.

Alum dose = 200 mg/L

TX – Fluoride Removal

0

1

2

3

4

0 120 240 360 480 600 720 840

Fluo

ride

Con

c. (m

g/L)

Time (min)

Influent = 3.48 mg/L

200 300 20Alum (mg/L)

MMWA, TX Steady State Values in Flocculation Effluent

Alum Dose (mg/L) pH F

(mg/L) %

Removal DOC

(mg/L) %

Removal 20 8.32 3.24 6 8.9 1

50 7.98 3.14 10 8.9 1

100 7.72 2.88 21 8.4 7

150 7.35 2.42 30 8.0 11

200 7.20 1.98 43 7.4 18

300 6.89 1.57 56 6.8 24

Manitou Springs, CO

Colorado Pilot Results

Alum Dose

(mg/L)

F Removal

(%)

Si Removal

(%)

Al Residual (mg/L)

UV-254 Removal

(%)

20 14.3 4.8 0.475 53

50 33.9 11.5 0.229 62

100 52.8 16.7 0.074 65

150 63.6 21.2 0.056 64

200 71.2 27.4 0.038 65 300 79.8 34.0 0.031 66

Effect of pH on Removals

pH F

Removal (%)

UV-254 Removal

(%)

6.5 71 65

7.5 51 54

Fluoride Removals Alum Dose

(mg/L)

Synthetic Water

CO Jar Test

CO Pilot

TX Jar Test

TX Pilot

20 17 12 14 6 6

50 30 34 34 18 10

100 46 48 53 35 21

150 71 74 64 56 30

200 80 81 71 70 43

300 86 87 80 83 56

Conclusions for Al Coagulation • Alum coagulation can be an effective treatment

process for lowering fluoride concentrations to acceptable levels. The optimum pH is 6.5.

• The impact of NOM on F removal is minimal. • Pilot tests of the Colorado Water were consistent with

Jar Tests and Synthetic water tests • Pilot tests for the TX water showed lower removals of F

than Jar tests due to differences in pH • F removal in jar tests with TX water were also lower

than the synthetic water tests due to differences in background water chemistry (e.g. low SUVA, high TOC, high alkalinity)

FeCl3 Coagulation

Objectives

• Quantify Fluoride Removal in iron coagulation systems

• Determine the effect of NOM surrogates on fluoride removal

• Determine the effect of NOM on fluoride removal

• Determine the effect of fluoride on removal of NOM

Bench-Scale Testing

• Synthetic Water • pH varied

– pH 4.0 – 6.5 (ΔpH=0.5) – Using NaOH, and HCl

• FeCl3 dose controlled

= 100mg/L and 200mg/L

• Organic acids - Pyromellitic acid - Phthalic acid - NOM

Comparison of Co-precipitation vs Pre-formed Fe(OH)3(s)

0

10

20

30

40

50

60

3 4 5 6 7

Fluo

ride

Rem

oval

(%)

pH

CPT (FeCl3=100mg/L)

CPT (FeCl3=200mg/L)

PRE (FeCl3=200mg/L)

FeFx Complexation

FeF2+ is a Key Player of Fe Coagulation

F-

FeF2+

FeF2+

Fluoride Removal

0

10

20

30

40

50

60

3 4 5 6 7

Fluo

ride

Rem

oval

(%)

pH

FluoridePhthalic+FluoridePyromellitic+FluorideNOM+Fluoride

Fluoride Removal at pH 4.0 Fluoride Pyromellitic+Fluoride

Phthalic+Fluoride NOM+Fluoride

Organic Removal – Phthalic acid

0

20

40

60

80

100

3 4 5 6 7

Org

anic

Aci

d Re

mov

al (%

)

pH

UV-Vis

PhthalicPhthalic+Fluoride

0

20

40

60

80

100

3 4 5 6 7

Org

anic

Aci

d Re

mov

al (%

)

pH

TOC

PhthalicPhthalic+Fluoride

Organic Removal – Pyromellitic acid

0

20

40

60

80

100

3 4 5 6 7

Org

anic

Aci

d Re

mov

al (%

)

pH

TOC

PyromelliticPyromellitic+Fluoride

0

20

40

60

80

100

3 4 5 6 7

Org

anic

Aci

d Re

mov

al (%

)

pH

UV-Vis

PyromelliticPyromellitic+Fluoride

Removal of NOM in Fe Coagulation

0

20

40

60

80

100

3 4 5 6 7

Org

anic

Aci

d Re

mov

al (%

)

pH

TOC

NOMNOM+Fluoride

0

20

40

60

80

100

3 4 5 6 7

Org

anic

Aci

d Re

mov

al (%

)

pH

UV-Vis

NOM

NOM+Fluoride

Conclusions • Fe coagulation

– Fluoride removals up to about 30% were observed. • Max removal at pH 4.5 • No reduction in removal in the presence of organic acids

– Effect of fluoride on organic acid removal is dependent on the organic acid and the pH/

• Compared to Alum coagulation

– More organic removal over the pH range – Max. fluoride removal at lower pH FeCl3=pH 4.5 , Alum=pH 6.5

• Recent report found elevated levels of arsenic throughout Texas drinking water systems

• Chromium-6 Found in Tap Water of 31 U.S. Cities (Dec. 2010)

• Enhanced Coagulation could be applied for Arsenic and Chromium removal

Texas Statesman: Arsenic persists in some Texas water supplies

Removal of Trace Metals in Enhanced Coagulation

Methodology

• Evaluate Removals in Freshly Precipitated and Pre-precipitated Systems in Increasingly Complex Systems – Single-Solute – Bi-Solute – Tri-Solute – Natural Systems

• Assess the Potential of DLM Surface Complexation Model for Predicting Removal

Predictions of Adsorption onto Hydrous Ferric Oxide AsT = 3.3e-6M, CrT = 2e-6M, CO3T = 0.01M

020406080

100

2 4 6 8 10

% A

dsor

bed

pH

Multicomponent Adsorption on Hydrous Ferric Oxide: Diffuse Layer

Model

As Cr CO3 As(SS)

0

0.000002

0.000004

0.000006

2 4 6 8 10M

oles

/L A

dsor

bed

pH

Multicomponent Adsorption on Hydrous Ferric Oxide: Diffuse Layer

Model

As Cr CO3 As(SS)

Single Solute arsenate pH sorption edge surface coverages (µmol/g) corresponding to 100 percent removal from solution

Adsorption Experiments on GFH

Solid (g/L) I.S. (M) Sorbate Max. Γ (μmol/g)

Buffer (M)

As 133 GFH 0.01 0.01 SiO2 111 NaHCO3 0.01

Ca2+ 2495 As 133

GFH 0.01 0.01 SiO2 1113 NaHCO3 0.01 Ca2+ 2495 As 133

E33 0.01 0.01 SiO2 111 NaHCO3 0.01 Ca2+ 2495 As 133

E33 0.01 0.01 SiO2 1113 NaHCO3 0.01 Ca2+ 2495

Estimation of Site Density E33* GFH*

Surface area from surface charge density comparisons (m2/g) 350 600

SSD, tritium exchange (sites/nm2) 2.51 1.43 SSD, anion maximum sorption (sites/nm2) 0.55 1.18

SSD, cation maximum sorption (sites/nm2) 1.90 1.70

log [H+]

-10.5 -10.0 -9.5 -9.0 -8.5 -8.0 -7.5 -7.0

0.01 M Ionic Strength0.1 M Ionic Strength0.5 M Ionic Strength0.01 M DLM titration fit0.1 M DLM titration fit0.5 M DLM titration fit

E33T = 10 g/L

NsT = 3.2 x 10-3 M

log [H+]

-11 -10 -9 -8 -7 -6 -5

TOT

H

-0.0020

-0.0015

-0.0010

-0.0005

0.0000

0.0005

0.0010

0.00150.01 M Ionic Strength0.1 M Ionic Strength0.5 M Ionic Strength0.01 MDLM titration fit0.1 MDLM titration fit0.5 MDLM titration fit

GFHT = 2 g/L

NsT = 2.35 x 10-3 M

DLM Fits to Titration Data Surface protolysis:

log K+ = 6.90; log K- = -8.96

pH6 7 8 9 10 11 12

Per

cent

Ca2

+ S

orbe

d0%

20%

40%

60%

80%

100%Ca2+T=1.96 ppm

Ca2+T=11.62 ppm

pH6 7 8 9 10 11 12

Per

cent

As

Sor

bed

0%

20%

40%

60%

80%

100%AsT=106 ppbAsT=518 ppbAsT=1981 ppb

GFHT = 0.01 g/L

I S = 0 02M

pH6 7 8 9 10 11 12

Perc

ent C

a2+

Sorb

ed

0%

20%

40%

60%

80%

100%Ca2+T=1.84 ppm

Ca2+T=11.6 ppm

GFHT = 0.01 g/L

pH4 6 8 10 12

Per

cent

SiO

2 S

orbe

d0%

20%

40%

60%

80%

100%SiO2,T=942 ppb; GFHT=0.1 g/LSiO2,T=1012 ppb; GFHT=0.01 g/LSiO2,T=8.98 ppm; GFHT=0.01 g/L

As(V) Si Ca

pH6 7 8 9 10 11 12

Per

cent

As

Sor

bed

0%

20%

40%

60%

80%

100% AsT = 103 ppbAsT = 522 ppb AsT = 2072 ppb

E33T = 0.01 g/L

GFH

E33

pH4 6 8 10 12

Per

cent

SiO

2 S

orbe

d

0%

20%

40%

60%

80%

100%SiO2,T=939 ppb; E33T=0.1 g/LSiO2,T=704 ppb; E33T=0.01 g/LSiO2,T=6.38 ppm; E33T=0.01 g/L

Bisolute Predictions on E33

pH6 7 8 9 10 11 12

Per

cent

As

Sor

bed

0%

20%

40%

60%

80%

100%E33T = 0.01 g/L

AsT=103 ppbSingle Solute Model AsT=102 ppb As; SIO2,T=696 ppbAsT=106 ppb As; SIO2,T=6.29 ppmBisolute Model Bisolute Model

pH6 7 8 9 10 11 12

Per

cent

As

Sor

bed

0%

20%

40%

60%

80%

100%

AsT=108 ppbSingle Solute Model AsT=111 ppb; Ca2+T=2.06 ppm

AsT=108 ppb; Ca2+T=11.7 ppm

AsT=111 ppb; Ca2+T=2.06 ppm model

AsT=108 ppb; Ca2+T=11.7 ppm model

E33T = 0.01 g/L

As/Si As/Ca

pH6 7 8 9 10 11 12

Per

cent

As

Sor

bed

0%

20%

40%

60%

80%

100%

AsT=103 ppbSingle Solute Model

pH4 6 8 10 12

Per

cent

Ca2

+ S

orbe

d

Ca2+T=1.96 ppmSingle solute model

pH4 6 8 10 12

Perc

ent S

iO2

Sorb

ed

SiO2,T=1012 ppbSingle Solute Model

AsT=113 ppb; Ca2+T=1.42 ppm; SiO2,T=11.5 ppm

AsT=113 ppb; Ca2+T=1.42 ppm; SiO2,T=11.5 ppm

Tri-Solute Predictions on E33

Summary

• Precipitation, complexation and adsorption in alum coagulation are intricately linked

• Most adsorption models examine aged precipitates

• Most precipitation models do not evaluate short term effects of adsorption

• Understanding the mechanisms of these precipitation and adsorption processes will allow better estimation of removals of contaminants in coagulation systems

Extra Slides

Effect of pH on Al Residuals

Fluoride Removal

Organic Removal

Fluoride Removal

Organic Removal

CO Water UV-254 Removal Alum Dose

(mg/L) Removal

(%)

20 33

50 40

100 47

150 50

200 51

300 55