Enhancement of Pollutant Enhancement of Pollutant Removal in Bioretention Removal in Bioretention Cells by Soil AmendmentCells by Soil Amendment

Glenn O. BrownGlenn O. Brown, , Professor, PE, Professor, PE, Ph.D., D.WREPh.D., D.WRE

Biosystems and Agricultural Biosystems and Agricultural EngineeringEngineering

Oklahoma State UniversityOklahoma State University

August 20, 2009August 20, 2009

BackgroundBackground Phosphorus and Nitrate removal in Phosphorus and Nitrate removal in

bioretention cells has been reported to bioretention cells has been reported to be highly variable, and in some cases, be highly variable, and in some cases, cells have been a P and NO3cells have been a P and NO3-- source. source.

Our long term objective hasOur long term objective hasbeen to find an inexpensivebeen to find an inexpensivefilter media with highfilter media with highpollutant sorption andpollutant sorption andadequate hydraulicadequate hydraulic conductivity. conductivity.

Materials and MethodsMaterials and Methods Soils: Dougherty sand, Teller loamSoils: Dougherty sand, Teller loam Sorbent media: fly ash, peat moss, limestone, Sorbent media: fly ash, peat moss, limestone,

expanded shales and sulfur modified iron.expanded shales and sulfur modified iron. Batch sorption experiments conducted to Batch sorption experiments conducted to

screen media.screen media. Hydraulic conductivity tests performed to Hydraulic conductivity tests performed to

determine infiltration capacity of media.determine infiltration capacity of media. Column study and transport modeling carried Column study and transport modeling carried

out to determine transport parameters and out to determine transport parameters and predict long-term cell performance. predict long-term cell performance.

Media ScreeningMedia Screening

Batch Sorption

Distribution coefficients were measured to screen media. Fly ash and an expanded shale from KS displayed the largest P sorption.

P Kd ml/gpHpH KKdd, mL/g, mL/g

Teller loamTeller loam 6.26.2 0.410.41

Dougherty Dougherty sandsand 6.36.3 2.082.08

Fly ashFly ash 11.11.55

21802180

LimestoneLimestone 9.09.0 12.112.1

Peat mossPeat moss 2.92.9 -5.79-5.79

M-shale (KS)M-shale (KS) 6.46.4 280280

N-shale (MO)N-shale (MO) 8.68.6 1.211.21

Heavy Metal Sorption, Heavy Metal Sorption, Kd (ml/g)Kd (ml/g)

MaterialMaterial CuCu PbPb ZnZn

Dougherty Dougherty sandsand

11.611.6 335335 88

Teller LoamTeller Loam 16501650 557557 351351

SlaughtervillSlaughterville Loame Loam

46804680 646646 113113

Fly AshFly Ash 84108410 30503050 40104010

Dougherty Dougherty SandSand

155155 >1220>1220 2121

D + 2.5% FD + 2.5% F 266266 >1220>1220 618618

D + 5% FD + 5% F 239239 >1220>1220 843843

Amending soils with fly Amending soils with fly ashash

The addition of fly ash increased P sorption of both The addition of fly ash increased P sorption of both soils significantly, especially Dougherty sand.soils significantly, especially Dougherty sand.

0

200

400

600

800

0 3 6 9 12

Fly ash content, %

Kd

, mL

/gTeller LoamDougherty Sand

5% fly ash

K s = 40.4e-0.484X

r2 = 0.999

0

10

20

30

40

50

0 2 4 6 8 10Fly ash content (X ), %

Ks, c

m/h

r

Hydraulic ConductivityHydraulic Conductivity Teller loam: 0.29 cm/hr; Dougherty sand: 40 cm/hr;Teller loam: 0.29 cm/hr; Dougherty sand: 40 cm/hr;

Expanded shale: 39 cm/hr. Expanded shale: 39 cm/hr. The addition of fly ash The addition of fly ash decreased decreased KKs s of Dougherty sand markedly.of Dougherty sand markedly.

5% fly ashKs= 3.59 cm/hr

Ks of sand/fly ash mixture

Falling head permeameter

P Sorption Isotherms P Sorption Isotherms

LangmuirLangmuir FreundlichFreundlich

SSmm, ,

mg/kgmg/kgbb, ,

L/mgL/mgrr22

KKff, ,

L/kgL/kgnn rr22

Dougherty Dougherty sandsand 23.823.8 0.2780.278 0.9480.948 4.934.93 0.6220.622 0.9140.914

M-shaleM-shale 82.082.0 3.303.30 0.9970.997 52.952.9 0.2540.254 0.9960.996

D+5%FD+5%F 385385 2.892.89 0.9980.998 203203 0.2950.295 0.9850.985

DesorptionDesorption Dougherty sand

desorbed average 42% of initially sorbed P, expanded shale 7%, and D+5%F negligible amounts.

Possible irreversible sorption in D+5% and shale.

Dougherty sand

0

50

100

150

200

3 6 11

SorptionDesorption

Expanded shale

0

50

100

150

200

3 6 11S

, m

g/kg

Sorption

Desorption

D+5%F

0

50

100

150

200

3 6 11

Initial P concentration, mg/L

Sorption

Desorption

Column ExperimentsColumn Experiments Column: 14.4 cm I.D., 14.3 cm long.

Loading rate: 3 cm/hr. Influent

concentration: 1 mg/L P.

Samples analyzed by ICP.

Evaluate sorption in a dynamic condition.

Transport ModelingTransport Modeling One dimensional linear equilibrium One dimensional linear equilibrium

adsorption convection-dispersion transport adsorption convection-dispersion transport model in CXTFIT 2.1 in the STANMOD model in CXTFIT 2.1 in the STANMOD software package developed by the U.S. software package developed by the U.S. Salinity Laboratory.Salinity Laboratory.

No decay, no production, third-type inlet No decay, no production, third-type inlet boundary and step input.boundary and step input.

Fit observed breakthrough curves by the Fit observed breakthrough curves by the model to estimate hydrodynamic dispersion model to estimate hydrodynamic dispersion coefficient (coefficient (DD) and retardation factor () and retardation factor (RR).).

P Column ResultsP Column Results

0.0

0.5

1.0

1.5

2.0

0 50 100 150 200 250 300 350 400

Pore volumes

Ce/Ci

Dougherty sand

D+2.5%F

D+5.0%F

Expanded shale

Fitted

Observed and fitted P breakthrough curves

P Column Results

DougherDougherty sandty sand

M-M-shaleshale

D+2.5D+2.5%F%F

D+5%D+5%FF

Retardation (Retardation (RR)) 11 1616 199199 470470

KKdd calc. from calc. from RR 00 1010 3838 8080

KKdd from batch from batch

sorp.sorp.2.12.1 280280 307307 398398

Metald Column Results Metald Column Results Only Zn was observed in the effluent Only Zn was observed in the effluent

after 250 to 350 pore volumes.after 250 to 350 pore volumes. Retardation estimated by destructive Retardation estimated by destructive

sampling of the columns and fitting sampling of the columns and fitting using using CXTFIT 2.1.CXTFIT 2.1. D+5%F

0

0.01

0.02

0.03

0.04

Cu observed Pb observed Zn observed Fitted

(c)

0 2 4 6 8 10 12 14

Distance (cm)

C

r (m

g L

)

-1

Metal Column ResultsMetal Column ResultsMediumMedium MetalMetal RR Kd (ml/g)Kd (ml/g)

Dougherty Dougherty sandsand

CuCu 11001100 264264

PbPb 2,3502,350 564564

ZnZn 490490 117117

D + 2.5% FD + 2.5% F CuCu 6,7006,700 1,3201,320

PbPb 7,1007,100 1,4001,400

ZnZn 2,0002,000 394394

D + 5% FD + 5% F CuCu 175,000175,000 29,00029,000

PbPb >2,950>2,950 >48,900>48,900

ZnZn 145,000145,000 24,00024,000

Estimating LifetimeEstimating Lifetime Hypothetical ScenarioHypothetical Scenario

Filter media depth: 1 mFilter media depth: 1 m Influent concentrations: P, Cu, Zn & Pb 1 mg/LInfluent concentrations: P, Cu, Zn & Pb 1 mg/L Effluent limits: P 0.037 mg/L; Cu, Zn & Pb 0.01 Effluent limits: P 0.037 mg/L; Cu, Zn & Pb 0.01

mg/l.mg/l. Fifty years of Grove OK precipitation data Fifty years of Grove OK precipitation data

were used to estimate the runoff loading.were used to estimate the runoff loading. Used fitted parameters from column tests.Used fitted parameters from column tests. Conservative assumption of reversible Conservative assumption of reversible

adsorption.adsorption.

Transport ModelingMedium Element

Lifetime (years)

Pavements Lawns

Doughertysand

Cu 22 62

Pb 48 133

Zn 10 27

D+2.5% F

Cu 96 264

Pb 102 280

Zn 28 79

D+5% F

Cu 1111 3050

Pb >1861 >5107

Zn 925 2539

P 4 11

Sulfur Modified IronSulfur Modified Iron

A variation of “zero valance iron”A variation of “zero valance iron” Shown to reduceShown to reduce

NitrateNitrate ArsenicArsenic ChromiumChromium Chlorinated SolventsChlorinated Solvents Other MetalsOther Metals

Screening tests Screening tests conducted in Spring of 2009.conducted in Spring of 2009.

SMI - Nitrate testsSMI - Nitrate tests

Batch reactor.Batch reactor. Two types of SMI.Two types of SMI. Pure SMI, and Pure SMI, and

mixed with sand mixed with sand and flyash.and flyash.

Solution Solution concentrations ofconcentrations of0 to 300 mg/l.0 to 300 mg/l.

SMI – Nitrate ResultsSMI – Nitrate Results

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

5% SMI Pure SMI 2.5% SMI 2.5% FA

50% SMI 50% FA

Per

cent

Red

uct

ion

SMI (1)SMI (2)Average

ConclusionsConclusions The addition of fly ash increased P sorption of all The addition of fly ash increased P sorption of all

soils significantly.soils significantly. Phosphorous sorption is at least partially Phosphorous sorption is at least partially

irreversible.irreversible. Soils tested have significant heavy metal sorption, Soils tested have significant heavy metal sorption,

but fly ash will make them effectively infinite sinks.but fly ash will make them effectively infinite sinks. Amended with 5% fly ash, Dougherty sand exhibited Amended with 5% fly ash, Dougherty sand exhibited

high P sorption and adequate hydraulic high P sorption and adequate hydraulic conductivity.conductivity.

Sulfur Modified Iron has potential to remove nitrate. Sulfur Modified Iron has potential to remove nitrate. We can assume it will also remove organic We can assume it will also remove organic compounds.compounds.