Abstract

A series of laboratory, field, and modeling studies were performed evaluating the potential for in situ aerobic cometabolism of chlorinated aliphatic hydrocarbon (CAH) mixtures, including 1,1,1-trichloroethane (1,1,1-TCA), 1,1-dichloroethane (1,1-DCA) and 1,1-dichloroethene (1,1-DCE) by bioaugmented microorganisms that grew on butane. A butane-grown bioaugmentation culture, primarily comprised of a Rhodococcus sp., was developed that effectively transformed mixtures of the three CAHs, under subsurface nutrient conditions. Microcosm experiments and modeling studies showed rapid transformation of 1,1-DCE with high transformation product toxicity and weak inhibition by butane, while 1,1,1-TCA was much more slowly transformed and strongly inhibited by butane. Field studies were conducted in the saturated zone at the Moffett Field In-Situ Test Facility in California. In the bioaugmented test leg, 1,1-DCE was most effectively transformed, followed by 1,1-DCA, and 1,1,1-TCA, consistent with the results from the laboratory studies. A 1-D reactive/transport code simulated the field responses during the early stages of testing (first 20 days), with the following extents of removal achieved at the first monitoring well; 1,1-DCE (97%), 1,1-DCA (77%), and 1,1,1-TCA (36%), with little or no CAH transformation observed beyond the first monitoring well. As time proceeded, decreased performance was observed. The modeling analysis indicated that this loss of performance may have been associated with 1,1-DCE transformation toxicity combined with the limited addition of butane as a growth substrate with longer pulse cycles. When shorter pulse cycles were reinitiated after 40 days of operation, 1,1-DCE transformation was restored and the following transformation extents were achieved; 1,1-DCE (94%), 1,1-DCA (8%), and 1,1,1-TCA (0%), with some CAH transformation occurring past the first monitoring well. Modeling analysis of this period indicated that the bioaugmented culture was likely not the dominant butane-utilizing microorganism present. This was consistent with observations in the indigenous leg during this period that showed effective butane utilization and the following extents of transformation: 1,1-DCE (86 %), 1,1-DCA (5%), and 1,1,1-TCA (0%). The combination of lab and field scale studies and supporting modeling provide a means of evaluating the performance of bioaugmentation and the cometabolic treatment of CAH mixtures.

Keywords: Cometabolism; Modeling; Field tests; Bioaugmentation; Butane; 1,1-Dichloroethene, 1,1-Dichloroethane; 1,1,1-Trichloroethane; Inhibition; Transformation toxicity; CAH mixtures

Nomenclature

Parameter

Definition

K_Ic,DCE,BUT

competitive inhibition constant of 1,1-DCE on butane (mg/L)

K_Ic,DCA,BUT

competitive inhibition constant of 1,1-DCA on butane (mg/L)

K_Ic,TCA,BUT

competitive inhibition constant of 1,1,1-TCA on butane (mg/L)

K_Ic,DCE,DCA

competitive inhibition constant of 1,1-DCE on 1,1-DCA (mg/L)

K_Ic,DCE,TCA

competitive inhibition constant of 1,1-DCE on 1,1,1-TCA (mg/L)

K_Ic,DCA,DCE

competitive inhibition constant of 1,1-DCA on 1,1-DCE (mg/L)

K_Ic,DCA,TCA

competitive inhibition constant of 1,1-DCA on 1,1,1-TCA (mg/L)

K_Ic,TCA,DCE

competitive inhibition constant of 1,1,1-TCA on 1,1-DCE (mg/L)

K_Ic,TCA,DCA

competitive inhibition constant of 1,1,1-TCA on 1,1-DCA (mg/L)

K_Ic,BUT,DCE

competitive inhibition constant of butane on 1,1-DCE (mg/L)

K_Ic,BUT,DCA

competitive inhibition constant of butane on 1,1-DCA (mg/L)

K_Ic,BUT,TCA

competitive inhibition constant of butane on 1,1,1-TCA (mg/L)

K_Iu,BUT,DCE

non-competitive inhibition constant of butane on 1,1-DCE (mg/L)

K_Iu,BUT,DCA

non-competitive inhibition constant of butane on 1,1-DCA (mg/L)

K_Iu,BUT,TCA

non-competitive inhibition constant of butane on 1,1,1-TCA (mg/L)

H_cc,DCE

dimensionless Henrys constant for 1,1-DCE

H_cc,DCA

dimensionless Henrys constant for 1,1-DCA

H_cc,TCA

dimensionless Henrys constant for 1,1,1-TCA

H_cc,BUT

dimensionless Henrys constant for butane

f_d

fraction of cells that are biodegradable (mg/mg)

d_c

cell decay oxygen demand (mg O₂/mg cell)

X

cell concentration on a pore volume basis (mg/L)

X₀

initial cell concentration on a pore volume basis (mg/L)

Y

cell yield (mg cells/mg butane)

b

cell decay coefficient (d⁻¹)

F_a

stoichiometric ratio of oxygen to butane for biomass synthesis (mg O₂/mg butane)

V_L

liquid volume (L)

V_G

gas volume (L)

K_la

overall gas/liquid mass transfer coefficient (d⁻¹)

k_m DCE

maximum transformation rate of 1,1-DCE (mg 1,1-DCE/mg cells-d)

k_m DCA

maximum transformation rate of 1,1-DCA (mg 1,1-DCA/mg cells-d)

k_m TCA

maximum transformation rate of 1,1,1-TCA (mg 1,1,1-TCA/mg cells-d)

k_m BUT

maximum utilization rate of butane (mg butane/mg cell-d)

C

aqueous substrate concentration (mg/L)

K_s DCE

half-saturation constant of 1,1-DCE (mg/L)

K_s DCA

half-saturation constant of 1,1-DCA (mg/L)

K_s TCA

half-saturation constant of 1,1,1-TCA (mg/L)

K_s BUT

half-saturation constant of butane (mg/L)

T_c DCE

transformation capacity of 1,1-DCE (mg 1,1-DCE/mg cells)

T_c DCA

transformation capacity of 1,1-DCA (mg 1,1-DCA/mg cells)

T_c TCA

transformation capacity of 1,1,1-TCA (mg 1,1,1-TCA/mg cells)

C^*

sorbed phase substrate concentration (mg substrate/kg soil)

D_h

hydrodynamic dispersion coefficient (m²/d)

F_k

mass transfer rate coefficient for sorption (d⁻¹)

v

average linear groundwater velocity (m/d)

K_d

partition coefficient for sorption (L/kg)

Φ

porosity

ρ_b

bulk density of the aquifer solids (kg/L)

Article Outline

Nomenclature

1. Introduction

2. Model development

3. Batch kinetic studies

3.1. Culture description

3.2. Batch transformation tests in media and microcosms

3.3. Analytical methods

4. Field tests

5. Results

5.1. Transformation of CAH mixtures in batch reactors with growth media

5.2. Transformation of CAH mixtures in groundwater/aquifer solids microcosms

5.3. Field experiments and model simulations

5.4. Bioaugmentation and biostimulation tests

6. Discussion

Acknowledgements

References