BIOAUGMENTATION CONSIDERATIONS - Bioaugmentation for Groundwater Remediation - page 143

Figure 5.2. Photo of direct push injection of bioaugmentation culture.
be the most feasible option. Shallower plumes or plumes in tight formations may favor the use
of direct injection of electron donor and culture.
Ideally, the spacing of injection wells/points should incorporate the expected transport
distances of the bioaugmentation culture to permit good distribution of the culture. However,
the transport of bioaugmentation cultures is still under study. Research using pure cultures
suggests that introduced microorganisms will be removed as a result of straining and filtration
processes within a short distance (inches to feet) from the point of introduction (Mawdsley
et al., 1996 ; Emelko et al., 2006 ). However, pilot and field studies have documented that
dehalorespiring bacteria can move through aquifer materials greater than 100 ft (30 m) from
the point of introduction (Major et al., 2002 ), suggesting that downgradient movement is due to
growth and detachment processes.
5.3.2 Preconditioning Requirements
Prior to injecting Dhc , it is important that the ORP and pH are suitable for growth and that
there is sufficient electron donor present. In the following sections, the selection and addition
of electron donors and buffers are discussed.
5.3.2.1 Selection and Addition of Electron Donors
Given the diversity of organisms contained within mixed consortia, most bioaugmentation
cultures can utilize a wide variety of electron donors in fermentative processes, typically
resulting in the conversion of the electron donor into molecular hydrogen and acetate. Dhc
depend primarily on hydrogen as the electron donor for dechlorination (L¨ffler et al ., 2003 )
although some dechlorinating populations also can utilize acetate (He et al., 2002 ). Non- Dhc
microorganisms present in mixed consortia play a significant role in supporting dechlorinating
activity through the production of hydrogen through fermentative processes.