PRODUCTION AND HANDLING OF DEHALOCOCCOIDES BIOAUGMENTATION CULTURES - Bioaugmentation for Groundwater Remediation - page 111

The amount of time required to achieve suitable conditions and the amount of electron
donor needed depends on conditions at the site, including oxygen levels and the presence of
other bacterial electron acceptors (e.g., nitrate, sulfate, ferric oxide [Fe 3+ ]). Some bioaugmenta-
tion treatments, however, have been performed without extensive aquifer pretreatment.
Because the consortia used for bioaugmentation contain fermentative and other facultative
aerobic microorganisms able to use oxygen, it is likely that these organisms rapidly use low
levels of DO, thereby protecting the oxygen sensitive Dhc organisms. In most cases of direct
injection, in situ distribution of the culture is aided by injecting anaerobic water following
culture injection.
3.7.2 Dilution
An alternative to direct injection of bacterial cultures into aquifers is to dilute them first
and inject over a long period of time or into many injection wells. In most cases, groundwater or
potable water is made anaerobic by adding electron donor to the water in a closed container and
incubating it until the bacteria in the water consume the DO. In the case of groundwater, the
number of bacteria present is sufficient to remove the oxygen in a few days. Potable water,
however, because of its low bacterial numbers can take quite long to become anaerobic. The
process can be accelerated by adding an inoculum of oxygen consuming bacteria. The inoculum
can be a commercially available culture. Injection water also can be made anaerobic by adding
soil, compost, or other readily available microbe rich material if necessary. Experience has
shown that free residual chlorine from chlorination in most potable waters is not inhibitory to
Dhc cultures (data not shown), but because of the potential variability of free chlorine in
drinking waters, testing treated potable water with the selected bioaugmentation culture is
recommended.
An alternative to using bacteria to remove residual DO from dilution water is to sparge
the containerized dilution water with nitrogen or argon. This approach can remove DO to
below 1 mg/L, but the ease of using this method depends on the volume of water being treated.
Argon may have an advantage over nitrogen because it is heavier than air and forms an
anaerobic gas blanket on top of the treated water, thereby preventing further dissolution
of oxygen into the water. This sparging approach also reduces levels of free chlorine in
potable water.
3.7.3 Mixing with Other Reagents Before Injection
Field personnel often desire to mix bioaugmentation cultures directly with electron donors
and/or reducing agents such as L-cysteine so that both can be injected simultaneously. The
compatibility of the bioaugmentation culture with high concentrations of electron donors and
reducing agents must be evaluated before using this approach. Initial testing has shown that
L-cysteine does not inhibit the SDC-9 TM consortium at concentrations up to 0.69 g/L (data not
shown). However, the pH of some electron donors is extreme (to avoid spoilage) and high
concentrations of some electron donors may be directly toxic to Dhc . For example, even typical
injection concentrations (10% as carbon) of five tested commercially available electron donors
inhibited SDC-9 TM in laboratory testing even after pH adjustment (data not shown). In addition
to direct inhibition, rapid fermentation of electron donor substrates can result in the production
of metabolic acids and CO 2, that reduce the pH of the mixture or recipient groundwater to
levels that can inhibit Dhc (McCarty et al., 2007 ; Vainberg et al., 2009 ). Therefore, if cultures