Enhancement of Pollutant Removal in Bioretention Cells by Soil Amendment Glenn O. Brown, Professor, PE, Ph.D., D.WRE Biosystems and Agricultural Engineering Oklahoma State University August 20, 2009

Background Phosphorus and Nitrate removal in bioretention cells has been reported to be highly variable, and in some cases, cells have been a P and NO3 - source. Phosphorus and Nitrate removal in bioretention cells has been reported to be highly variable, and in some cases, cells have been a P and NO3 - source. Our long term objective has been to find an inexpensive filter media with high pollutant sorption and adequate hydraulic conductivity. Our long term objective has been to find an inexpensive filter media with high pollutant sorption and adequate hydraulic conductivity.

Materials and Methods Soils: Dougherty sand, Teller loam Soils: Dougherty sand, Teller loam Sorbent media: fly ash, peat moss, limestone, expanded shales and sulfur modified iron. Sorbent media: fly ash, peat moss, limestone, expanded shales and sulfur modified iron. Batch sorption experiments conducted to screen media. Batch sorption experiments conducted to screen media. Hydraulic conductivity tests performed to determine infiltration capacity of media. Hydraulic conductivity tests performed to determine infiltration capacity of media. Column study and transport modeling carried out to determine transport parameters and predict long-term cell performance. Column study and transport modeling carried out to determine transport parameters and predict long-term cell performance.

Media Screening Batch Sorption Distribution coefficients were measured to screen media. Fly ash and an expanded shale from KS displayed the largest P sorption. P K d ml/gpH K d, mL/g Teller loam Dougherty sand Fly ash Limestone Peat moss M-shale (KS) N-shale (MO)

Heavy Metal Sorption, Kd (ml/g) MaterialCuPbZn Dougherty sand Teller Loam Slaughterville Loam Fly Ash Dougherty Sand 155> D + 2.5% F 266> D + 5% F 239>

Amending soils with fly ash The addition of fly ash increased P sorption of both soils significantly, especially Dougherty sand. The addition of fly ash increased P sorption of both soils significantly, especially Dougherty sand. 5% fly ash

Hydraulic 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. The addition of fly ash decreased K s of Dougherty sand markedly. 5% fly ash K s = 3.59 cm/hr K s of sand/fly ash mixture Falling head permeameter

P Sorption Isotherms LangmuirFreundlich S m, mg/kg b, L/mg r2r2r2r2 K f, L/kg n r2r2r2r2 Dougherty sand M-shale D+5%F

Desorption 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.

Column 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 Modeling One dimensional linear equilibrium adsorption convection-dispersion transport model in CXTFIT 2.1 in the STANMOD software package developed by the U.S. Salinity Laboratory. One dimensional linear equilibrium adsorption convection-dispersion transport model in CXTFIT 2.1 in the STANMOD software package developed by the U.S. Salinity Laboratory. No decay, no production, third-type inlet boundary and step input. No decay, no production, third-type inlet boundary and step input. Fit observed breakthrough curves by the model to estimate hydrodynamic dispersion coefficient (D) and retardation factor (R). Fit observed breakthrough curves by the model to estimate hydrodynamic dispersion coefficient (D) and retardation factor (R).

P Column Results Observed and fitted P breakthrough curves

P Column Results Dougherty sand M-shaleD+2.5%FD+5%F Retardation (R) K d calc. from R K d from batch sorp

Metald Column Results Only Zn was observed in the effluent after 250 to 350 pore volumes. Only Zn was observed in the effluent after 250 to 350 pore volumes. Retardation estimated by destructive sampling of the columns and fitting using CXTFIT 2.1. Retardation estimated by destructive sampling of the columns and fitting using CXTFIT 2.1.

Metal Column Results MediumMetalR Kd (ml/g) Dougherty sand Cu Pb2, Zn D + 2.5% F Cu6,7001,320 Pb7,1001,400 Zn2, D + 5% F Cu175,00029,000 Pb>2,950>48,900 Zn145,00024,000

Estimating Lifetime Hypothetical Scenario Hypothetical Scenario Filter media depth: 1 m Filter media depth: 1 m Influent concentrations: P, Cu, Zn & Pb 1 mg/L Influent concentrations: P, Cu, Zn & Pb 1 mg/L Effluent limits: P mg/L; Cu, Zn & Pb 0.01 mg/l. Effluent limits: P mg/L; Cu, Zn & Pb 0.01 mg/l. Fifty years of Grove OK precipitation data were used to estimate the runoff loading. Fifty years of Grove OK precipitation data were used to estimate the runoff loading. Used fitted parameters from column tests. Used fitted parameters from column tests. Conservative assumption of reversible adsorption. Conservative assumption of reversible adsorption.

Transport Modeling MediumElement Lifetime (years) PavementsLawns Dougherty sand Cu2262 Pb48133 Zn1027 D+2.5% F Cu96264 Pb Zn2879 D+5% F Cu Pb>1861>5107 Zn P411

Sulfur Modified Iron A variation of “zero valance iron” A variation of “zero valance iron” Shown to reduce Shown to reduce Nitrate Nitrate Arsenic Arsenic Chromium Chromium Chlorinated Solvents Chlorinated Solvents Other Metals Other Metals Screening tests conducted in Spring of Screening tests conducted in Spring of 2009.

SMI - Nitrate tests Batch reactor. Batch reactor. Two types of SMI. Two types of SMI. Pure SMI, and mixed with sand and flyash. Pure SMI, and mixed with sand and flyash. Solution concentrations of 0 to 300 mg/l. Solution concentrations of 0 to 300 mg/l.

SMI – Nitrate Results

Conclusions The addition of fly ash increased P sorption of all soils significantly. The addition of fly ash increased P sorption of all soils significantly. Phosphorous sorption is at least partially irreversible. Phosphorous sorption is at least partially irreversible. Soils tested have significant heavy metal sorption, but fly ash will make them effectively infinite sinks. Soils tested have significant heavy metal sorption, but fly ash will make them effectively infinite sinks. Amended with 5% fly ash, Dougherty sand exhibited high P sorption and adequate hydraulic conductivity. Amended with 5% fly ash, Dougherty sand exhibited high P sorption and adequate hydraulic conductivity. Sulfur Modified Iron has potential to remove nitrate. We can assume it will also remove organic compounds. Sulfur Modified Iron has potential to remove nitrate. We can assume it will also remove organic compounds.