Remediation Technologies - Environmental Investigation and Remediation - page 344

degraded in the bioreactor tests. In the highly organic water, the removal rates were lower than in the
blended water, suggesting that toxic chemicals in the more contaminated water may have had
an inhibitory effect on the biodegradation of both 1,4-dioxane and THF. The removal rate was as
high as 97.5% for 1,4-dioxane and 99.3% for THF in the blended water tests, but only 87.3% and
97.9%, respectively, in the highly organic water. Although the i eld pilot-testing indicated successful
reduction of 1,4-dioxane, below the detection limit in some cases, the detection limit was 360 μ g/L,

well above health-based and regulatory cleanup criteria in many states and EPA regions.
Evans et al. (2006) measured the specii c activity of 1,4-dioxane metabolized by CB1190 at 0.33 g/

min per milligram of protein. A variety of bioreactor coni gurations was tested to measure maximum
achievable biodegradation rates under optimized conditions. The bioreactors used the microbe strain
CB1185, a mixed culture that includes CB1190, grown in batch on BSM with initial 1,4-dioxane con-
centrations of 5000 mg/L and fed additional 1,4-dioxane as needed to maintain the required biomass
and growth rate. Reactors supported by silica sand were inoculated with 100 L cultures containing
2500 mg of protein per liter. The dimensions of the packed-bed reactor were 0.5 ft in diameter and
10 ft in height; the groundwater l ow rate was 0.5-0.8 L/min, and the air-l ow rate was 2 L/min. Evans
et al. measured the best performance in the sequence batch reactor with biomass carriers. Biodegradation
rates were slow, and reactor efi ciency declined over time, possibly because of bacteria washout, low
temperatures, toxic contaminants or by-products, and imbalance between the rates of bacteria growth
and die-off (Evans et al., 2006). Table 7.1 presents a summary of the laboratory testing results of vari-
ous bioreactor designs and 1,4-dioxane concentrations for inl uent and efl uent.
Microvi Biotech LLC has developed a process that removes 1,4-dioxane from groundwater in an in
situ biobarrier or an ex situ bioreactor (F. Shirazi, written communication, 2007). This treatment uses
Rhodococcus sp., which under aerobic conditions can degrade 1,4-dioxane as the sole carbon or energy
source, without the addition of a secondary substrate (Cowan et al., 1994, as referenced in Zenker et al.,
2000). The bacteria are isolated, grown on glucose, and encapsulated in a porous polymeric matrix to
increase survivability, reduce bacterial washout, and provide an improved environment for the stability
and longevity of the bacteria. Figure 7.7 shows a scanning electron microscope photograph of the encap-
sulated microorganisms within the matrix. Preliminary research and bench testing demonstrated that

μ

TABLE 7.1
Laboratory Bioreactor Results Summary

1,4-Dioxane
Out
(mg/L)

1,4-Dioxane
In (mg/L)

Biodegradation
Rate a Bioreactor Run Time (h)

Activated sludge with recycle 60 100 0.42 1.8

Activated sludge with recycle 43 1200 270 24

RBC 55 91 1.0 1.8

RBC 55 5000 1800 54

Packed bed reactor < 9 100 < 0.04 12

Packed bed reactor < 9 2 < 0.05 0.24

Sequencing batch reactor 24 100 < 1.0 1.8

Sequencing batch reactor
with biomass carriers

12 1200 < 1.0 250

Fluidized bed reactor 15 10 117

<1.0

Source: Evans, P.J., Parales, R.E., and Parales, J.V., 2006, 18th Symposium in Groundwater Resources Association Series
on Groundwater Contaminants: Emerging Contaminants in Groundwater: A Continually Moving Target, June 7-8,
2006 . Concord, CA. Housed at the University of California Water Resources Archives, Berkeley, CA.
a Units are milligrams of protein per liter per hour.