The Past, Present and Future for Selenium Treatment

2008 WV AMD Task Force MeetingJames J. Gusek, P.E.,Kevin W. Conroy, P.E.,Thomas Rutkowski, P.E.

Where is it found? Health Food Store Shelves Paint, pigments, dye formulating Electronics Glass manufacturing Insecticide production Pulp and paper Ash piles, FGD blowdown, Coal/oil combustion Agricultural water Petroleum processing Mining operations (1st noted in

ASMR paper, 1988)

What’s the problem?

Aquatic life hazard1983 – Kesterson National Wildlife

Refuge - CaliforniaBirth defects/death of birds, small

animals, fishSelenium cycle not well understood

Uncertainty on bioavailabilityEven if bio-available, what is toxic?

Often times low concentration, high volume - makes treatment expensive

How is it regulated?

5 µg/L Freshwater aquatic life 50 µg/L Primary DWS MCLU.S. Fish and Wildlife Service has

recommended 2 µg/L to protect fish, waterfowl and endangered aquatic species

Chemistry

4 primary oxidation states elemental selenium Se0

-2 selenide Se-2

+4 selenite (HSeO3- and

SeO3-)

+6 selenate (SeO4-2)

Chemical equilibrium principals don’t really apply

Driven byRedox conditionsBiological activitySorption processes

Overburden Geochemistry

Dzharkenite (FeSe2) (analogous to pyrite)

An organic diselenideSelenium-substituted pyrite

Three Selenium Mineral Phases ID’d in Western US Phosphate Resource Area

Ref: Ryser, et al., 2005

Factoid #2: Se precipitation in treatment systems is typically believed to be Se0

Factoid #1: Oxidized Se in weathered shale overburden originally started as selenium mineral analogous to pyrite

Past and Present - EPA BAT

Ferric coagulation/filtrationTypically pH <7Co-precipitation effectEffective removal requires

reduction of selenate to seleniteProblem if arsenic present

Lime softeningRever$e o$mo$i$

Non-preferential processPretreatment due to other typical

mine water issues may be required

Past and Present - EPA BAT

ElectrodialysisAlumina

Selenite adsorbed at pH range of 3 – 8

Silica can interfere at pH >4Selenate adsorption is poor

Ion exchangeNeed oxidized divalent selenateCompeting ion effects can hinder

effectivenessSome specialty resins tested

Past and Present - EPA BDAT

Ferrihydrite precipitation with concurrent adsorption of selenium on the ferrihydrite surface

For adsorption – need ferric ion (Fe+3) present

Most effective removal at pH 4-6Somewhat effective up to pH 8Phosphate, silicate, arsenic,

carbonate can interfere

Past and Present – EPA/DOE MWTP

Selenium Treatment/Removal Alternatives Demonstration

Report issued in 2001Three technologies tested in field

Ferrihydrite Adsorption (baseline)Catalyzed CementationBiological Reduction

One technology tested on bench scale

Enzymatic Reduction

Past and Present – EPA/DOE MWTP

Objective – treat to <50 µg/L SeWork done in 1999-2001Basis – Kennecott Utah Copper

Corp’s Garfield Wetlands-Kessler Springs site

<50 to >10,000 µg/L Se 95%+ selenateTDS 1,000 - 5,000 mg/L

Past and Present – EPA/DOE MWTP

FerrihydriteDid not work on a consistent basisVarious iron types, concentrations

and ratios usedCould achieve objective but at

prohibitive reagent consumptionQuestions on TCLP stability

Past and Present – EPA/DOE MWTP

Catalyzed cementationDeveloped for arsenic, selenium,

thallium removalRemoves metals by cementation

on the surface of iron particlesBelieved to work on both selenite

and selenateProprietary catalysts usedBench test work had shown

favorable resultsDid not work on a consistent basis

Past and Present – EPA/DOE MWTP

Biological Reduction (BSeR™)Used anaerobic solids bed

reactors Selenium reduced to elemental

selenium by biofilms and proprietary microorganisms

Molasses used as carbon sourceWas able to consistently meet

objectiveOver 70% of samples less than

detection (2 µg/L)

Past and Present – EPA/DOE MWTP

Economics

BDAT Cementation BSeR™Capital $1.0M $1.1M $0.6M

O&M $2.1M $1.2M $0.14M

NPV $17M $9.5M $1.1M

$/1,000 gal $13.90 $8.17 $1.32

$/kg Se $1,836 $1,079 $174Based on 300 gpm plant, 2 mg/L selenium influent

2001 dollars

2005 price for Se = $110/kg

Problems With the Past and Present

Non-selective processesLarge amounts of secondary wasteMultiple reagentsOkay for bulk selenium removal with

other metalsCan’t consistently get to <10 µg/L

Biological Reduction – GeneralStudied for decades (1994 ASMR)

Microbes degrade/transform contaminant because

Se used as energy sourceDetoxification mechanism for bugsResembles another ion (sulfate)Combination of the above

Anaerobic reactorsReduction to elemental seleniumNitrate/sulfate interference?Facilitated with iron presence?

90%+ removal reported

Biological Reduction – Ponds/Wetlands

Panoche Drainage District – San Joaquin Valley

74-1,400 µg/L due to Se rich soilPrimarily selenate formNumerous bioremediation studiesAlgal-Bacterial Selenium Removal

(ABSR)Anoxic ponds – reduce selenate to

selenite to elemental and settleGenerally about 80% maximum

removal

Biological Reduction – Ponds/Wetlands

Additional California work - 2005Constructed wetlands9 plant species tested63% - 71% removal~20 µg/L influent, 3 – 6 µg/L

effluent

Problem with ponds/wetlandsHRT’s in days

Biological Reduction – Advances

More selective microbes isolatedAdvances in fixed film/biofilm

mediaBetter understanding of operating

conditionsResult – retention times have

been reduced from days to hours for active systems

Advances also made in passive technology

Biological Reduction – Advances

ABMet®Offered by GE Water and Process

TechnologiesSame as BSeR™ processSeveral FGD projects at

commercial scale3,000 – 5,000 µg/L seleniumUp to 20,000 mg/L chloride98% – 99% removal projectedEffluent as low as 10 µg/L

Passive treatment =

What Is Passive Treatment?

If It’s Not a BLACK BOX, What Is Passive Treatment?

It’s the: Sequential Ecological eXtraction

Of metals in a man-made but naturalistic bio-system

Early Passive Treatment Data

Site/ Date

GPM pH Influent Se ug/L

Effluent Se ug/L

Percent Removal

NV Gold Tailing (Aerobic) 1994

10 7.5 40 16 60%

NV Waste Rock (BCR)1994

6 2.7 22 <5 >78%

Brewer Mine (BCR)1995

1 2 1,500 50 97%

Biological Reduction – AdvancesPassive Selenium Reducing BioreactorTested on Colorado Western SlopeBureau of Reclamation Science and Technology ProgramFIW Influent typically ~20 µg/LSpike to 70 µg/L2006-2007

1,000-2,000 mg/L SO4-2 background

Biological Reduction – 2007Passive Selenium Reducing Bioreactor Four reactors with different substrate

compositions Organic substrate composed of wood chips,

hay, manure ZVI incorporated; no advantage 12 hour detention time adequate, optimization

possible Operated for 20 weeks Effluent typically <2 µg/L Up to 98% removal 1 gpm pilot to be built June 2008 Full Scale unit costs: $0.26 per 1000 gallons or

$115 per kg Selenium Design similar to sulfate reducing bioreactor

BCR Construction in Montana

Designed for nitrate, thallium, and selenium

Biological Reduction – Advances

Active Anaerobic Bioreactor SystemWaste rock seepage250 gpm capacityFixed film bioreactor with high

surface area mediaMolasses used as carbon sourcePhosphate/urea addedReverse osmosis system used

during high flow – 700 gpmBioreactor feed switched to RO brine

Biological Reduction – Advances

Active Anaerobic Bioreactor System 18 hour retention timeLow flow (raw seepage)

Se ~30 µg/LSO4

-2 ~6,000 mg/L

High flow (RO brine)Se ~70 µg/LSO4

-2 ~13,500 mg/L

Biological Reduction – Advances

Costs: $5.71 per 1,000 gallons (RO~$4.40?)$50,000 per kg Se removed (v. dilute)

Biological Reduction – Advances

Building (RO, filters) 50ft x 135ft

Bioreactors160ft x 60 ft

Overall120ft x 200 ft or

0.55 acres

Biological Reduction – Advances

Active Anaerobic Bioreactor System Effluent goal is 10 µg/LPilot plant operated for 7 monthsHigh sulfide was an issue

Discharge qualitySolids fouling

Full scale system designed and constructed

Operating for about 18 months Compliant water being produced

Future?Selenium with other metals

Conventional lime-iron based processes for bulk removal

Biological polishing processLow concentration selenium

Biological reductionBoth active and passive options

Combinations with other processes – i.e. membranes

Reduce costs to <$5.00/Kgal? Maybe down to $0.25/Kgal with passive BCRs?

Future?

Insitu Selenium Treatment (NOT bugs on Booze)

Partial Treatment to Meet Goals?

Biological Reduction – Application Keys

Nutrients are vital in establishing microbial population

Understanding of site chemistry and environmental interactions (e.g., hydrogeology)

Analytical methodsCan get discrepancies in total and

dissolvedPossibly related to digestionVolatile selenide

Need for aerobic post-treatmentHigh COD, P, N

Conclusions

There is no silver bullet for selenium removal to low levels

Selenium can be removed to

<10 µg/LAll sites must be evaluated

individuallyPure “paper” designs are risky –

bench & pilot development work always recommended

Cost of selenium reduction to low levels is decreasing

Questions?