Copyright [insert date set by system] by [CH2M HILL Entity] • Company Confidential

Biochemical Reactors for Selenium Treatment

James Bays, PWS, SEBT Thomas, Ph.D.Derek Evans, P.E.

EPA National Conference on Mining-Influenced Waters

Albuquerque, New Mexico

August 12-14 2014

Overview of Presentation

Outline

� Selenium Transformations, Wetland Examples

� Selected Recent Pilot Systems

� New Full Scale System Detailed review

� O&M Overview

� Constraints Review

� Summary

NAMC Selenium Report 2010

http://www.namc.org/docs/00062756.PDF

Selenium Passive Treatment Systems:Free Water Surface Wetlands Provide Starting Point

� Area: 36 ha

� Flow: ~6,540 m3/d

� Date: since 1991

� HRT: 7-10 days

� Se reduction: 89%

� Se in: 20-30 µg/L

� Se out: <5 µg/L

� Volatilization: 10-30%

Chevron’s Water Enhancement Wetland, Richmond CAChevron’s Water Enhancement Wetland, Richmond CA

Hansen et al, 1998

Treatment Wetlands: Multiple Processes, Multiple Scales

Surface Water

Plant Uptake & Storage

Adsorption

Nitrification /Denitrification

Decomposition

Burial & Soil Storage

Sedimentation

Volatilization

PrecipitationSediments

Detritus

N, BOD, VolatileOrganics,Selenium

P, Metals

NO3, NH3

ON, NH3, P, Metals, OrganicsDiffusion

Metals, N, P

TSS, Adsorbed Contaminants

Annual Growth Cycle

Natural Oxidation/Reduction Processes in Flooded Organic Soils

� Aerobic respiration

– ½ O2 + 2e- + 2H+ -> H2O

� Denitrification

– 2NO3- + 12 H+ +10e- -> N2+6H2O

� Manganese reduction:

– MnO2 + 4H+ + 2e- ->Mn2+ + 2H2O

� Iron reduction:

– Fe(OH)3 + 3 H+ + 2e- -> Fe2+ + 2H2O

� Sulfate reduction:

– SO42- + 10H+ +8e- -> H2S + 4H2O

� Methane production:

– CO2 + 8 H+ + 8e- -> CH4 +2 H2O

Process Eh (mV)

Aerobic respiration +330

Denitrification +220

Manganese reduction +200

Ferric to ferrous reduction +120

Sulfate reduction -150

Methanogenesis -250

Organic carbon substrate provides electrons via microbial process

Progress in Design ofTreatment Wetlands and Passive Systems

1993 1996 2006 20091989 2000

1990 2000 2010

ASMR

Hedin, R.S., R.W. Nairn, and R. Kleinmann.

Passive treatment of coal mine

drainage.

USBM 9389

Hedin, R.S., R.W. Nairn, and R. Kleinmann.

Passive treatment of coal mine

drainage.

USBM 9389

ASMR

IMWA

v. 36(11)

Biochemical Reactors - Definitions

ITRC 2013

� …engineered treatment

system that uses an

organic substrate to drive

microbial and chemical

reactions to reduce

concentration of metals,

acidity, and sulfate in mine-

impacted water.

Pulles 2009

� A water treatment system

that utilizes naturally

available energy sources

such as topographical

gradient, microbial

metabolic energy,

photosynthesis and

chemical energy and

requires regular but

infrequent maintenance to

operate successfully over

its design life.

Biochemical Reactors – Sustainable Treatment Through Naturally Renewable Components

� Wood

– Chips, sawdust

� Grass

– Hay

� Wetland Plants

– Bulrush, cattail

� Manure and Soil

� Natural Power

– Gravity

– Solar

ITRC 2013

Progress in Biorechemical Reactor Design

Denitrifying Bioreactors for Agricultural Wastewater Treatment

Pilot Projects

Full-Scale Sequential Systems

www.sdcornblog.com

www.nps.gov

Bob Nairn

Mayer Ranch, OK

Wetland Processing and Storage of Selenium

Org-Se

SeO42-

SeO32-

Se0

HSe-1

(CH3) 2Se

Dissimilatory Reduction

SeO42- → SeO3

2- → Se0 → Se2-

� Distribution in wetland sediments:� 0:13:41:46

� 89-92% reduction from selenate to elemental Se in 10 - 16 days

Volatilization

� Organic + SeO32-→ (CH3)2Se

� Volatilized from plant tissues

� 5-30% cumulative loss from sediments and plants

Sorption

� Selenite sorbs to sediments and soil constituents: Fe-, Mn- or Al-

oxyhydroxides and organic matter

Plant Uptake

� Rapid uptake

� Tissue concentrations increase but not detrimental

� No long term storage in plants; Se transferred to sediments

Precipitation

� Abiotic precipitation with S-

BCR Example: Anaerobic “Bioreactor” Wetland Demonstration Showed High Efficiency in Minimal Area

� Source: gravel pit seep

� Volume: 4,380 ft3

� Flow: 2-24 gpm

� Date: 9/08-10/09

� HRT: 2.4 d

� Se in flow 1-34 µg/L

� Se reduction: 98% (90% winter)

� Se removal rate: 16 mg/d/m3

� Se out: 0.5 µg/L

� TCLP <1 µg/L Se

Walker and Golder. 2010. US Bureau of Reclamation

Grand Junction COGrand Junction CO

Two outlets assigned stringent selenium discharge standard:

4.7 ug/L monthly mean8.2 ug/L daily max

Recent SeBCR Case Histories: Pilot and Full-Scale Passive Treatment in West Virginia

PTS 2: Jul 2011

PTS 14: Nov 2011

Pilot Study Demonstrated Target Compliance By Media Bioreactors

MaterialPilot Barrel

A B C DWoodchips -- 20% 16% 20%Sawdust -- 20% 47% 30%

Hay -- 15% 16% 20%Organic Peat -- 20% -- --

Sphagnum Moss 100% 20% -- --Composted Manure -- -- 15% 23%

Limestone Chips -- 5% 6% 7%

Total (by volume) 100% 100% 100% 100%

23.5

14.0

3.23.9

2.4

0

5

10

15

20

25

Barrel

Se µ

g/L

Inflow

A (Peat)

B (OM)

C (OM)

D (OM)

Upflow Media Bioreactors (200 L)

4.7µg/L

Vertical Distribution and Speciation of Selenium: Reduction, Sorption, Volatilization

0

1

2

3

4

5

6

7

8

9

10

0

1

2

3

4

5

6

7

8

9

10

To

tal

Se

len

ium

(m

g/

kg

)

Se

len

ium

(m

g/

kg

)

Substrate Selenium Speciation

Salt Weakly adsorbed S2Se/Elemental Se Selenides Total Se

123% 88%105%131%87% 88%

Percent Recovery of Sequential Extractions versus the total digests

87% 105% 108% 88% 94%

0

1

2

3

4

5

6

7

8

9

10

0

1

2

3

4

5

6

7

8

9

10

To

tal

Se

len

ium

(m

g/

kg

)

Se

len

ium

(m

g/

kg

)

Substrate Selenium Speciation

Salt Weakly adsorbed S2Se/Elemental Se Selenides Total Se

123% 88%105%131%87% 88%

Percent Recovery of Sequential Extractions versus the total digests

87% 105% 108% 88% 94%

Source:CH2MHILL (2012)

InOutInOutIn

Removal Rates Estimated Based on HRT

Zero-order volumetric

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

12 16 20 24

Sele

niu

m R

em

oval

(mg

/d/m

3)

HRT (hrs)

A

B

C

D

First-order area-based

0

50

100

150

200

250

300

350

400

450

500

12 16 20 24

k1

(m/y

r)

HRT (hrs)

A

B

C

D

PTS 2: Design Flow Set to Capture Load and Account for Inter-annual Variation

54.5

545

5450

5.45

ug/L

; gpm m

3d

-1

Full-scale System Designed Based on Pilot Results: Gravity Flow and Sequential Process

PTS 2 Plan and Profile Design Concepts

� Replace existing sediment pond

�30 gpm base flow

� Four cells-in-series:1. Downflow biochemical reactor

2. Anaerobic upflow wetland

3. Fill-and-drain wetland

4. Aerobic surface flow marsh

12

34

Source:

CH2MHILL (2912)

Cell 1: Downflow Biochemical Reactor (BCR)

Plan Profile

m2 Type Media Plants Function

526

Downflow biochemical

reactor

Mixed organic

NoneSelenium reduction

m2 Type Media Plants Function

567Upflow

anaerobicPeat

Sedges, rush

Selenium reduction, Byproduct polishing

Cell 2: Upflow Anaerobic Wetland

Plan Profile

Cell 3: Subsurface Flow Gravel Bed

Plan Profile

m2 Type Media Plants Function

648

Subsurface fill and drain

Limestone gravel

CattailsByproduct polishing

Cell 4: Free Water Surface Wetland

Plan Profile

m2 Type Media Plants Function

445Free water

surface

Topsoil and

pondedwater

CattailsByproduct polishing

PTS 2 Selenium Meeting Daily Criterion Year-Round

µg/L In Ou

t

Average 10.24 1.32

Max 14.47 2.57

Min 5.53 0.90

Range 8.9 1.7

0

5

10

15

20

25

30

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

F-11 S-11 A-12 O-12 M-13 N-13 J-14

Tem

pera

ture

(˚C)T

ota

l S

e (

µg

/L)

[Se]OUT Daily Max [Se]IN T (C°)

PTS 2 Selenium Meeting Monthly Criterion

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

F-11 S-11 A-12 O-12 M-13 N-13 J-14

Co

ncen

tratio

n R

ed

uctio

nTo

tal S

e (

µg

/L)

[Se]OUT Monthly Avg [Se]IN % Removal

87% CR

PTS 2 Selenium Not Significantly Affected by Flow

0

20

40

60

80

100

120

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

D-11 A-12 J-12 O-12 J-13 M-13 A-13 N-13 M-14 J-14

Flo

w (g

pm

)To

tal S

e (

µg

/L)

[Se]OUT Q (gpm)

Outlet 002 Selenium Accepting Significant Load Variation

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

D-11 A-12 J-12 O-12 J-13 M-13 A-13 N-13 M-14 J-14

Lo

ad

(g/d

)To

tal S

e (

µg

/L)

[Se]OUT Load (g)

PTS 2 Removal Rate Sustaining Target Range

y = 1.00x

y = 0.52x

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

Mass R

em

oved

(g

/d)

Mass Loading (g/d)

Polishing Wetlands Reduced Turbidity by 83%

1

10

100

1000

J A S O N D

Tu

rbid

ity (

NT

U)

Inf Cell 2 Cell 4

Cell 2

Cell 3 into Cell 4

On Balance, Natural Systems Favored(Coal Mine Drainage Example)

NaturalSystems

ConventionalSystems

•BCR+wetland footprint fits (just)•Construction $762K•Natural processes•O&M $15K/yr

•Can be made to fit•Construction $18MM•Engineered processes•O&M $500K

PTS 14: Higher Flow, Higher Concentration, Still Compliant with Criteria

� Five cells-in-series:1. 0.12 ac Head tank

2. 0.48 ac Upflow BCR

3. 0.30 ac Upflow BCR

4. 0.23 ac Surface flow marsh

5. 0.38 ac Sedimentation pond

�230 gpm base flow

�24 µg/L mean Se to <4.7

Source:CH2MHILL (2011)

Passive Treatment Operations & Maintenance:Basic Expectations

� Safety

– Access, walkway, railings

� Hydraulic Control

– Control structures, pipes, valves

� Process Performance Monitoring

– Intermediate sampling

� Site Maintenance

– Berms, liner & drainage

� Media

– Long-term replacement

• Can assume 20 yrs

• Cap in place an option

– Can supplement media/carbon

– TCLP – not hazardousImage Source

Bays, J. (2012)

� Physical

– Winter flow

– Summer flow

� Chemical

– Oxidized Nitrogen

– Solids

– Salinity

– Composition

– pH, ORP, DO

� Biological

– Establishment

Need to Identify Constraints Limiting Performance

Pilot Studies Recommended

Image source: 1 Bays, J. (2012)

Prospects Reasonable for Passive Treatment of Seleniferous Wastewaters

� Minewater quality

– Amenable to passive treatment with appropriate design

– Pilot studies recommended

� Reliable, natural anaerobic biological process

– Selenium will be reduced, sequestered year-round

� Learn from real-world examples

– Agriculture, mine-water, water treatment, power

� Cost-effective

– Small footprint, lower cost, less maintenance effort

Sources of Additional Information

ITRC Bioreactor Guidance 2013

NAMC Selenium Technology 2010 (update 2012)

http://www.namc.org/docs/00062756.PDFhttp://www.itrcweb.org/miningwaste-guidance/to_bioreactors.htm

Acknowledgements

Thanks to all of our collaborating private & public partners in the mining and power generation industries.

Contact: Jim Bays

813-281-7705

Email: Jim.Bays@ch2m.com

Sequential Systems Total Installed Cost1

Cost Considerations (Class 5 AACEI)Scenario: 200 gpm, 50 ug/L Sein, 5 ug/L

Seout

Biochemical Reactors (0.76 ac)

Subsurface Flow Beds

(0.77 ac)

y = 0.0812x0.6

0

1

10

10 100 1000

Capital C

ost ($

Mill

ion)

Flow Rate (GPM)

200 gpm~$2 MM

Sources: 1 CH2MHILL (2013) NAMC Update

1600

gpm

1800

gpm

Full scale Se

Cost Curve1

y = 2.123x0.6

1

10

100

1000

10 100 1000 10000

Cost per

Year

($ T

housand)

Flow Rate (GPM)

Cost Component

0%0% 3%

48%

8%

40%

Organic media, Cell 1. supplement

P media

Organic media, Cell 1. removal

Labor - Zone

Conceptual O&M Costs (Class 5 AACEI)200 gpm, 50 ug/L Se

200 gpm$51k/yr

Sources: 1 CH2MHILL (2013) NAMC Update

Full scale Se

FGD Bioreactor Pilot StudyMidwest Power Utility

0

20

40

60

80

100

120

0 0.25 0.5 0.75 1

To

tal S

e (

µg

/L

Fractional Area

P50

Model

Cell 11

k 289 m/yrzm 0.45C* 1 ug/L

0.250.25

0.50.5

1.51.5

0.25

VDF

0.250.25

11

0.25

VUF

Organic media

Gravel

Organic media

Sand

Gravel0.250.25

1.51.5

0.250.25

1.51.5

SSF SSF

0.25 0.25

Aggregate

Selenium Reduction Cells Secondary Parameter Cells

Sources: 1 CH2MHILL (2013)

Passive Treatment Concept1

TDS 2-10 g/L

Se in 129 – 290 ug/L

TDS 2-10 g/L

Se in 129 – 290 ug/L

FGD Ash Pond

Vertical Distribution of Retained Mass

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.00% 20% 40% 60% 80% 100%

Su

bstr

ate

Dep

th F

racti

on

Percent Total Mass

Mixe

dO

rga

nic

Pe

at +

SD

Sa

nd

Flo

wD

irectio

n

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.00% 20% 40% 60% 80% 100%

Su

bs

tra

te D

ep

th F

rac

tio

n

Percent Total Mass

Mixe

dO

rga

nic

Pe

at +

SD

Sa

nd

Flo

wD

irectio

n

Sources: 1 CH2MHILL (2013)

Saline Example: Continuous Se Removal BDL in Mixed Organic Media for RO Membrane Concentrate

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

Co

ncen

trati

on

(m

g/L

)

Bin 2 Influent (RO Conc.) Bin 2 Effluent

TDS ~8 g/L

Se in 20 µg/L

Nitrate-N in 55 mg/L

TDS ~8 g/L

Se in 20 µg/L

Nitrate-N in 55 mg/L

Sources:

CH2MHILL (2012)

Image Source:

Bays, J. (2012)