Handbook of Solvents - George Wypych - ChemTech - Ventech!

23.2 Remediation technologies 1619
Figure 23.2.1. Aerobic degradation of fluorene. A typical aerobic
biodegradation processes, using fluorene as the example where the
compound is completely mineralized. Here, fluorene is utilized as a
sole source of carbon and energy for microbial growth. Two pathways
for fluorene degradation by Arthrobacter sp. Strain 101 as suggested
by Casellas et al. [M. Casellas, M. Grifoll, J.M. Bayona, and
A.M. Solanas, Appl Environ Microbiol, 63(3), 819 (1997)].
tions under aerobic (presence of
oxygen), hypoxic (low oxygen),
and anaerobic (absence of oxygen)
conditions. Examples of recognized
biogeochemical reaction
sequences are summarized in Figures
23.2.1 and 23.2.2. Some of
these biological reactions are
co-metabolic meaning that the microbes
that catalyze them do not
gain carbon or energy for growth
and must therefore have a primary
carbon source available to drive
the processes.
Our ability to understand
and capitalize on biological processes,
such as biotransformation,
in in situ and ex situ strategies, often
result in a low cost, simple alternative
to conventional
treatment strategies. Several
methods to better understand
these processes, including direct
measure of microbial activity, 11
transformation of tracer compounds
into CO2 or metabolic in-
termediates, 12
and microbial
utilization of specific carbon
sources through stable isotopes
measurements 13 have been developed
and applied to a number of
hydrocarbon-impacted sites.
Other indirect measurements used
in the 1970’s and 1980’s such as
plate counts have led investigators
to believe that biodegradation was occurring, where direct measurements of biodegradation
were not conducted to support those conclusions. Furthermore, the use of plate counts
grossly underestimates the population of catabolically relevant biomass. 1 Biodegradation
likely occurs in most systems, however the level of biodegradation may be insufficient to
expect reasonable cleanup to target levels in the desired time frames.
The fact that HCs are amenable to aerobic biological treatment has been fully and convincingly
established in the scientific literature (see also recent review 1 ). In the absence of
oxygen as an electron acceptor, microbially catalyzed reductive dehalogenation of CHC has
been documented. 14-19 Recently, Yang and McCarthy 20 have demonstrated the reductive
dechlorination of chlorinated ethenes at H 2 tension too low to sustain competitive growth of
hydrogenotrophic methanogens. Anaerobic biotransformation of non-chlorinated HCs typ-