economical approach to treatment of soluble and ...economical approach to treatment of soluble and...

Economical Approach to Treatment of Soluble and Particulate As, Cu, Zn, and Cr in Stormwater Runoff to Meet BCWQGs AW

Presented by Elena Ranyuk, PhD MBAOctober 12, 2017 | RemTech 2017 | Banff, AB

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Heavy metals pollutants & BCWQGs

Our case study

- Overview

- Treatment method selection

- Phase I: Co-precipitation with an Al coagulant

- Phase II: Packed bed adsorption

Key Learnings

Overview

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Hardness –dependent guidelines are calculated at 100 ppm calcium hardness; D: dissolved T: total

Long-term BCWQGs for the Protection of Freshwater Aquatic Life (Approved & Working 2016)

Cu 4 ppb As 5 ppb

Zn 15 ppb Se 1 ppb

Cr 1 ppb for Cr(VI) 8.9 ppb for Cr(III)

Fe 1000 ppb for T 350 ppb for D

Pb 6 ppb Mn 1045 ppb

Cd 0.12 ppb for D Hg 0.01 when MeHg = 1.0% of THg

Co 4 ppb Ni 96 ppb

Ag 0.05 ppb Sn 0.008 ppb (organotin comp.)

Heavy Metals Pollutants

3

Our Case Study

BCWQG (LT) @ H=100

Intake – Dissolved Metals

Cu 4 ppb 2-850 ppb; average = 300

As 5 ppb 2-160 ppb; average = 65

Zn 15 ppb 10-250 ppb; average = 150

Cr 1/8.9 ppb 2-425 ppb; average = 74

TREATMENT OBJECTIVE:

• Achieve BCWQGs for Protection of Freshwater Aquatic Life

• Must be economical

• 100 gpm (6.3 L/s) continuous flow treatment

INCOMING WATER PROFILE:

• Neutral pH• Varying concentrations of soluble and particulate

As, Zn, Cu, & Cr

CLIENT:

• Medium size business in British Columbia

• Limited funds available

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Technical complexity

Cost

• Different optimal conditions for different water profiles

• Fluctuations in water intake affect the outcome

• Periodic regeneration of IX resin required

• Mgmt. of liquid waste streams

• Pre-treatment required

• Generation of ~30% of “reject” is typical

• Other waste streams require mgmt.

• Comprehensive pre-treatment required

• Different wastewater sources may require different adsorbents & EBCT

• Removal of TSS & optimal pH requiredC

HA

LLEN

GES

ChemicalPrecipitation

MembraneFiltration

Adsorption

Common Metal Removal Methods

Ion Exchange

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• Different optimal conditions for different water profiles

• Fluctuations in water intake affect the outcome

• Periodic regeneration of IX resin required

• Mgmt. of liquid waste streams

• Pre-treatment required

• Generation of ~30% of “reject” is typical

• Other waste streams require mgmt.

• Comprehensive pre-treatment required

• Different wastewater sources may require different adsorbents & EBCT

• Removal of TSS & optimal pH requiredC

HA

LLEN

GES

ChemicalPrecipitation

MembraneFiltration

Adsorption

Common Metal Removal Methods

Ion Exchange

1 2

6

Effluent w/lower

metal conc’n

Zn2+ + NaOH ---> Na+ + Zn(OH)2 (s) Soluble zinc Zinc hydroxide

Phase 1: Chemical Precipitation Method

Zn(OH)2 Precipitate by A. Lambert Photography

Coagulate Flocculate Settle ClarifyColloidal

metal precipitate

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1 ppb

10 ppb

100 ppb

1000 ppb

Co

nce

ntr

atio

n o

f d

isso

lve

d m

eta

l (m

g/L

)

pH

Source: EPA 625/8-80-003

Chemical Precipitation: Minimum Solubility

Theoretical solubilities of metal hydroxides as a function of pH

pH0.1 ppb

8

1 ppb

10 ppb

100 ppb

1000 ppb

Co

nce

ntr

atio

n o

f d

isso

lve

d m

eta

l (m

g/L

)

pH

Source: EPA 625/8-80-003



Zn

pH0.1 ppb

Minimum solubility

100 ppb

BCWQG for Zn at H=100

15 ppb

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1 ppb

10 ppb

100 ppb

1000 ppb

Co

nce

ntr

atio

n o

f d

isso

lve

d m

eta

l (m

g/L

)

pH

Source: EPA 625/8-80-003



Cd

BCWQG for CdpH

Minimum solubility

0.1 ppb

1 ppb

0.12 ppb

10

1 ppb

10 ppb

100 ppb

1000 ppb

Co

nce

ntr

atio

n o

f d

isso

lve

d m

eta

l (m

g/L

)

pHSource: EPA 625/8-80-003



Pb

BCWQG for Pb at H=100

pH

Minimum solubility

0.1 ppb

6 ppb

6000 ppb

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1 ppb

10 ppb

100 ppb

1000 ppb

Co

nce

ntr

atio

n o

f d

isso

lve

d m

eta

l (m

g/L

)

pH

Source: EPA 625/8-80-003



Cu

BCWQG for Cu at H=100

pH Minimum solubility0.1 ppb

4 ppb

12

4 ppb

In most cases, ACTUAL solubilities > THEORETICAL solubilities due to:

Incomplete reactions

Different optimal pH points for precipitation of different metals

Poor separation of colloidal precipitates

Formation of soluble metal-complexes with naturally occurring & androgenic chelates

Chemical Precipitation in “Real Life”

Hence, in practice, the GAP is likely to be even LARGER

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ACTUAL solubilities MAY be LOWERED due to

co-precipitation & adsorption processes

M3+ + H2O Mn(OH)m(H2O)x(3n-m)

Amorphous “floc” of aluminum/iron(III) hydroxide

Cu, Zn, Cd are adsorbed best at high pH

Oxyanions (AsO43-, CrO4

-, SeO32-) are adsorbed best at low pH

Process is focused on pH and coagulant dosages rather than on the solubilities of each metal

Enhanced Metal Removal with Al/Fe Coagulants

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OBJECTIVE: To optimize Cu and Zn co-precipitation with Al/Fe hydroxide

TEST CONDITIONS:

Phase 1: Co-precipitation Optimization Study

Intake sample

Dissolved/total Cu 540/760 ppb 20% chelated

Dissolved/total Zn 200/220 ppb

pH 6.5

Independent variables in the study

pH Coagulant Coagulant concentration

Detection method

portable photometer YSI9300 + colorimetric reagents kits

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Test pH Al coag. #1 Al coag. #2 Fe coag.Diss. Cu, % Removal

Diss. Zn, % Removal

#1 7 300 ppm 81% 50%#2 8 300 ppm 52% 90%#3 9 300 ppm 63% 90%#4 8 100 ppm 70% 70%#5 10 200 ppm 48% 90%#6 8 100 ppm 74% 35%#7 9 100 ppm 74% 90%#8 10 200 ppm 81% 65%#9 8 300 ppm 100 ppm 67% 85%

#10 9 300 ppm 100 ppm 85% 90%#11 10 300 ppm 100 ppm 74% 90%

Phase 1: Co-precipitation Optimization Study

#1 vs. #10• Fewer steps (2 vs 4)• As(VI) and Cr(VI) removal is known to be better at lower pH (but

limited testing possible with a photometer)16

Phase 1: Chemical Precipitation and Filtration

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Average Removal, %Metal Total Dissolved

As 83% 76%Cr 93% 87%Cu 85% 83%Zn 48% 18%

Phase 1: Field Results

As Cr Cu Zn

ppb

IN

OUT

BCWQG (LT)

Dissolved Cu

Particulate Cu

IN

OUT

BCWQG

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Discharge conc’nof As, Cu, Zn, Cr

> BCWQGs

PROS

• Simplicity

• Low capital cost

CONS

• Operating costs can be high

• Partial or complete system shut-down required to replace media

Phase 2: Fixed Bed Adsorption Method

Source: http://encyclopedia.che.engin.umich.edu

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OBJECTIVE: optimize Cu and Zn adsorption

TEST CONDITIONS:

Phase 2: Adsorption Optimization Studies

Pre-treated intake sample (Phase I conditions)

Dissolved/total Cu 160/160 ppb 20% chelated

Dissolved/total Zn 200/200 ppb

pH 6.5

Independent variables in the study

Combination of Adsorbents

Detection method

portable photometer YSI9300 + colorimetric reagents kits

RESULTS: a combination of adsorbents was found to reduce Cu and Zn to below detection limit (20 ppb)

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Phase 2

Phase 2: Fixed Bed Adsorption

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Phases 1+2: Field Results

BCWQG (ST) Discharge BCWQG (ST) Discharge BCWQG (ST) Discharge

Hardness 8.3 71 103

Volume treated, L 326,115 900,826 3,982,130 As 5 0.1 5 <0.1 5 2.12

Cr (VI+III) 1 <0.5 1 <0.5 1 <1.0

Cu 2.78 0.8 8.67 1.1 11.68 12.0

Zn 30 <5 30 <5 42.75 42.5

Below the Maximum

Within 5% of the Maximum

Exceeds Maximum by more than 5%

#1 #2 #3

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Volume treated, LBCWQG (ST) Discharge BCWQG (ST) Discharge BCWQG (ST) Discharge

Hardness

As 5 0.1 5 <0.1 5 2.12

Cr (VI+III) 1 <0.5 1 <0.5 1 <1.0

Cu 2.8 0.8 8.7 1.1 11.7 12.0

Zn 30 <5 30 <5 42.8 42.5

#1 #2 #3

326,115 900,826 3,982,130

8.3 71 103

129

35

191

139

391

1.6

82

120

0.1 0.1 2.1 0.8 1.15.0 5.0 5.0 5.0 5.0

99.9% 99.7%98.9%

99.4% 99.7%

96.1%

85.7%

97.4%96.4%

98.7%

75.0%

80.0%

85.0%

90.0%

95.0%

100.0%

105.0%

0

50

100

150

200

250

300

350

400

450

Nov.3/2016 Nov.14/2016 Jan. 24/2107 Feb. 2/2017 Feb. 15/2017

PP

B

ARSENIC Total MetalsTest Results & Removal Levels

Intake (PPB) Phase 1 (PPB) Phase 2 (PPB)

BCWQG Std Phase 2 (% remov) BCWQG (% remov)

Phase 1+2: Field Results for As

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43.718.6 24.1

152.0

591.0

1.4

90.9

201.0

0.0 0.0 0.0 0.0 1.11.0 1.0 1.0 1.0 1.0

100.0% 100.0% 100.0% 100.0%99.8%

97.7%

94.6%

95.9%

99.3%

99.8%

91.0%

92.0%

93.0%

94.0%

95.0%

96.0%

97.0%

98.0%

99.0%

100.0%

101.0%

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0


PP

B

CHROMIUM Total MetalsTest Results & Removal Levels



Phase 1+2: Field Results for Cr

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475.0

208.0

74.5

636.0

1280.0

14.9

483.0507.0

0.8 1.1 12.0 8.3 14.22.8 8.7 11.7 10.2 6.7

99.8% 99.5%

83.9%

98.7% 98.9%99.4%

95.8%

84.3%

98.4%99.5%

75.0%

80.0%

85.0%

90.0%

95.0%

100.0%

105.0%

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

1400.0


PP

B

COPPER Total MetalsTest Results & Removal Levels



Phase 1+2: Field Results for Cu

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146.0

79.0

90.1

167.0

230.0

72.0

180.0

103.0

0.0 0.0

42.537.6

50.7

30.0 30.0

42.8

30.0 30.0

100.0% 100.0%

52.8%

77.5% 78.0%79.5%

62.0%

52.5%

82.0%

87.0%

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

120.0%

0.0

50.0

100.0

150.0

200.0

250.0


PP

B

ZINC Total MetalsTest Results & Removal Levels



Phase 1+2: Field Results for Zn

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Chemical Co-Precipitation is a cost effective method for lowering metals conc’ns

Chemical Co-Precipitation alone is unlikely to be sufficient to meet BCWQGs for

many heavy metals, including Cu, Zn, Cr, & As

Chemical Co-Precipitation + Adsorption = a proven effective way to meet

BCWQGs (for this project at ~ 20-30% cost of an RO system)

Intake profile and contamination source play a very important role in treatment

process design

Key Takeaways

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Questions and Answers

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economical approach to treatment of soluble and ...economical approach to treatment of soluble and...

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