Bioremediation of contaminant source zones in groundwater has received significant attention in the past 5 years. The main concern is how high concentrations and even pure phase contaminants at source zones may hinder the biodegradation by indigenous microbial communities (Sleep et al. 2006). Even though some cultures, like KB-1, can degrade TCE at concentrations close to solubility limits, it is expected that high and pure phase of concentrations of contaminants, such as chlorinated solvents and hydrocarbons, can slow down and even stop biodegradation. Therefore, when high concentrations exist, an initial treatment step is required.
Recent research has shown that the rates of contaminant removal of biodegradation would still be slow relative to other agressive technologies such as nZVI, ISCO, or STAR. On the other hand, at low contaminant concentrations, these technologies become increasingly less cost-effective. Sites treated with these aggressive technologies are often subject to contaminant rebound at the termination of treatment due to diffusion from low permeability regions, slow dissolution from NAPL, and slow desorption from soils.
Our objective is to develop methods that can foster in situ bioremediation as a polishing step for each of these more aggressive technologies. This would represent a major step forward in groundwater remediation technology. One of the main advantages of microbial processes is their self-sustaining nature (Sleep et al. 2005), requiring in many cases no additional input of energy and nutrients to maintain effective long-term contaminant plume control. However, the effects of the high mass removal technologies on simultaneous and subsequent biological activity are not currently well understood (Hrapovic et al. 2005). The removal of large amounts of contaminant mass makes the subsurface environment less toxic, and the treatments often liberate substantial amounts of soil organic carbon and other nutrients to sustain biological growth. On the other hand, treatments such as STAR, NZVI, and ISCO may also kill indigenous microbial populations, and may produce initial geochemical conditions not favourable to bioremediation of the remaining contaminants. The re-establishment of biological activity may require active bioaugmentation, or rely on recolonization of the treatment area with suspended biomass carried into the treated zone by groundwater from the surrounding subsurface. The development of methods and expertise to design and implement combined treatment technologies coupling aggressive technologies like STAR, NZVI, and ISCO to in situ bioremediation is one of the main goals of this research project.