Remediation Technologies - Environmental Investigation and Remediation - page 345

FIGURE 7.7

Encapsulated microorganisms shown inside MicroBead. (From F. Shirazi, personal communi-

cation, 2007.)

the isolated Rhodococcus sp. was capable of degrading 1,4-dioxane in concentrations of greater than
10,000 g/L in less than 50 h ( Figure 7.8 ); however, the effectiveness at lower 1,4-dioxane concentra-

tions has not been demonstrated. The rate of 1,4-dioxane degradation per day (46,000-56,000

μ

g/L)
was maintained for more than 300 days in the laboratory reactor without preconditioning the bacteria
to 1,4-dioxane or adding any substrate to support cometabolic biodegradation.

μ

7.6.6 A NAEROBIC B ACTERIA
The anaerobic degradation of 1,4-dioxane was evaluated under iron-reducing conditions involving
anaerobic sludges by Pan and Chen (2006) of Zhejiang University in Hangzhou, China. They deter-
mined that the iron-reducing bacteria present in the anaerobic sludge could intrinsically degrade
40% of 1,4-dioxane in the microcosm without the need for amendments. Adding humic substances,
which may have acted as a carbon source, stimulated the anaerobic degradation of up to 70% of the
1,4-dioxane present. The degradation was caused by iron-reducing bacteria in which Fe(III) was
available as an electron acceptor. 1,4-Dioxane biodegradation was greatest in the presence of added
humic substances and Fe(III) under all the redox conditions. Complete degradation of 1,4-dioxane
was observed (Pan and Chen, 2006).
Shen et al. (2008) presented additional information related to their studies of iron-reducing
bacteria for 1,4-dioxane degradation. The degradation observed was determined to be entirely
from biological activity, because sterile conditions resulted in no statistically signii cant declines
in 40 days. Degradation of 1,4-dioxane in reactors incubated with iron-reducing bacteria derived
from the anaerobic sludge resulted in a decline of 25% (from 13 mg/L) over 40 days with no
amendments. Introduction of Fe(III) oxide caused a decline of 37% and adding Fe(III) oxides
and humic acids led to a reduction of 62% over the 40-day period. The humic acids are thought
to act as a catalyst, promoting biodegradation by the iron-reducing bacteria, rather than creating
reducing conditions, as is common in biodegradation of other contaminants, such as chlorinated
VOCs. A second set of experiments conducted after the initial 40-day period, using the same
inoculated bottles but replenishing 1,4-dioxane up to 50 mg/L, resulted in even higher daily