treatment mitigation

8/12/2019 Treatment Mitigation

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Mitigation of Acid Forming Materials

Active TreatmentActive Treatment

Passive TreatmentPassive Treatment

Other Water Quality Mitigation AlternativesOther Water Quality Mitigation Alternatives Acid SoilsAcid Soils


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ACTIVE Water Treatment Unit Operations

Neutralization

Aeration

Precipitation

Settling (solid/liquid separation)

Sludge dewatering

Sludge disposal


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Modern Hydrated Lime Treatment Plant

Treats 30,000 L/minute air asam tambang


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Aeration and Oxidation


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Settling (Solid/Liquid Separation)

Inclined Plate Clarifiers

Dissolved Air Flotation

Thickeners

Ponds or Basins

Clarifiers


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A. Passive Treatment ConceptsA. Passive Treatment Concepts

Aerobic WetlandsAerobic Wetlands

Settling Ponds/BasinsSettling Ponds/Basins

Anoxic Limestone Drains (Anoxic Limestone Drains (ALDALD))

Vertical Flow Wetlands (Vertical Flow Wetlands (VFW or SAPSVFW or SAPS)) Open Limestone ChannelsOpen Limestone Channels

Diversion WellsDiversion Wells

OxicOxic oror PyrolusitePyrolusite Limestone BedsLimestone Beds


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Disadvantages of Passive Treatment Disadvantages of Passive Treatment

Treatment area (hectares) neededTreatment area (hectares) needed

Highly acidicHighly acidic (>500 mg/l)(>500 mg/l) mine water problematicmine water problematic

It isIt is stillstill a developing science & technologya developing science & technology

Does not work well on large flowsDoes not work well on large flows

(design flows < 2000 L/minute)(design flows < 2000 L/minute) High construction costs at beginning (lot ofHigh construction costs at beginning (lot of rupiahrupiah

Some maintenance required (someSome maintenance required (some rupiahrupiah))


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Designing a Passive System Designing a Passive System

Water ChemistryWater Chemistry::

-- Determines the design or techniqueDetermines the design or technique

Net Alkaline Water Aerobic Treatment

Net Acidic Water Anaerobic Treatment

Discharge Flow RateDischarge Flow Rate::

--Determines the sizeDetermines the size


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Monitoring AMD Discharges


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Classifying Mine WaterClassifying Mine Water

Net AlkalineNet Alkaline, Fe contaminated, Fe contaminated

Net AlkalineNet Alkaline, Fe andFe and MnMn contaminatedcontaminated

Neutral pH net AcidNeutral pH net Acid, Fe and, Fe and MnMn contaminacontamina

Low pH AcidicLow pH Acidic, Fe andFe and MnMn contaminatedcontaminated

Low pH AcidicLow pH Acidic, Fe,Fe, MnMn, Al contaminated, Al contaminated


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Typical Section of anAerobic Wetland


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Aerobic Wetland Treatment System - Westmoreland County, PA

Net Alkaline Discharge Treatment


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Making Acid Water AlkalineMaking Acid Water Alkaline

1. Anoxic Limestone Drain (ALD)1. Anoxic Limestone Drain (ALD)

2. Vertical Flow Wetland (VFW)2. Vertical Flow Wetland (VFW)

3. Diversion Wells3. Diversion Wells

4. Open Limestone Channels4. Open Limestone Channels

5.5. OxicOxic ((PyrolusitePyrolusite) Limestone Beds) Limestone Beds


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How is alkalinity generated?

Limestone + Acidity Calcium ion + Bicarbonate Alkalinity

CaCO3 + H+ Ca 2+ + HCO3

-

Organic Carbon + Sulfate Hydrogen sulfide + Bicarbonate

Alkalinity

2 CH2O + SO4- H2S + 2 HCO3

-

Sulfate Reducing Bacteria (SRBs)

(2 H+) (H2CO3*)


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Limestone Dissolution is Slowand Solubility Limited

Limestone Dissolution is Slowand Solubility Limited

1212--18 hours of contact time18 hours of contact time Rule Of ThumbRule Of Thumb::0.30.3--0.6 metric ton Limestone/hour of contact/Liter0.6 metric ton Limestone/hour of contact/Literminute of flowminute of flow

Maximum concentration of alkalinity isMaximum concentration of alkalinity isgenerally 150generally 150--350 mg/L350 mg/L ((actual value isactual value isdependent on limestone source and water quality)dependent on limestone source and water quality)

Need large quantities of limestoneNeed large quantities of limestone(1,000(1,0002,000 metric tons not uncommon)2,000 metric tons not uncommon)

*


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Typical Section of an ALD


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Anoxic Limestone Drain Under Construction


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ALD SIZING CRITERIA

Retention time (Retention time (typically 16 hrs)typically 16 hrs)LimestoneLimestone

dissolution lossesdissolution losses

TypicalTypical ALD dimensions & configurationsALD dimensions & configurations

Limestone bed depth: 1Limestone bed depth: 1--2 meters2 meters

Drain width: 3Drain width: 3--20 120 1--6 meters6 meters Length to Width ratio: L:W = 2Length to Width ratio: L:W = 2 -- 20:120:1

PVC or plastic linerPVC or plastic liner

Impervious soil (clay) cap (1 meter)Impervious soil (clay) cap (1 meter)

Consider settling basin at ALD outlet for metals collectionConsider settling basin at ALD outlet for metals collection

*


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2. Vertical Flow Wetlands(VFWs)

2. Vertical Flow Wetlands(VFWs)

Overcomes limitations ofOvercomes limitations of ALDsALDs forforgenerating alkalinitygenerating alkalinity

Vertical flow through an organic layer and anVertical flow through an organic layer and anunderlying limestone bedunderlying limestone bed

Adds alkalinity through bacterial sulfateAdds alkalinity through bacterial sulfate

reduction and limestone dissolutionreduction and limestone dissolution Highly acid water can be treated by passageHighly acid water can be treated by passage

through a series ofthrough a series of VFWsVFWs


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Typical VFW Cross-Section


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Typical VFW Treatment System

Sed. PondVertical

Flow

Wetland

Sed. PondAerobic

Wetland

(optional)*

discharge

AMD Source

* Typically a sediment pond/vertical flow wetland system

combination is 80-90 % efficient in removing iron; therefore,

an aerobic wetland is recommended for further iron removal.

Flush

Pond


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VFW Treatment System - Centre County, PA

AMD source (influent)

Sed. Pond #1

Aerobic Wetland #1

VFW #1

Sed. Pond #2

Aerobic Wetland #2

VFW #2Sed. Pond #3

Treated effluent


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Typical Parameters:

a. Water depth = 0.15 1.5m

b. Organic layer = 0.15 0.6 m

c. Limestone depth = 0.45 1.5 m


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Typical Treatment System Costs, U.S.

Alkaline DischargesAlkaline Discharges

$490 per ton of iron treated per year$490 per ton of iron treated per year Moderately Acidic discharges (acid loads 100Acidic Discharges (acid loads > 100

tons/year)tons/year)

$295 per ton of acid treated per year$295 per ton of acid treated per yearAnoxic Limestone DrainsAnoxic Limestone Drains

$600 per ton of acid treated per year$600 per ton of acid treated per year


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Treatment SystemConstruction Costs,U.S.

Aerobic wetlands and settling pondsAerobic wetlands and settling ponds $50,000$50,000 -- $100,000 / hectare$100,000 / hectare CompostCompost

wetlands and SAPSwetlands and SAPS

$100,000$100,000 -- $150,000 / hectare$150,000 / hectare

Anoxic Limestone DrainsAnoxic Limestone Drains

~$15~$15 -- $30 / ton of LS Placed$30 / ton of LS Placed


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ACTIVE MINE PIT-Water Management


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WATER MANAGEMENT

Erosion and Sediment ControlErosion and Sediment Control Infiltration BarriersInfiltration Barriers

Caps: synthetic, grouts, claysCaps: synthetic, grouts, clays

Ground water interceptorsGround water interceptors

Drains and trenchesDrains and trenches

Induced RechargeInduced Recharge

Direct recharge through alkaline materialDirect recharge through alkaline material


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Acid Mine Soils

Add Lime, Soil Cover or Both


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Root Growth Stopped in Acid Minesoils


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Lime Application to Acid Minesoil


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Lime Placed One meter Deep in Acid Minesoil


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