Roadblocks to the implementation of biotreatment strategies

The Department of Defense (DoD) has over 21,000 contaminated sites requiring some form of remediation. Contaminants on these sites include explosive compounds (i.e., TNT, RDX, HMX), chlorinated solvents (i.e., PCE, TCE, TCA), polycyclic aromatic hydrocarbons (i.e., benzo-a-pyrene), and polychlorinated biphenyls (i.e., aroclors). Current technology has centered around incineration, air stripping, and the use of activated carbon. Frequently, this technology is not cost effective nor publicly acceptable. Biotreatment offers a possible alternative. Biotreatment can cost effectively eliminate contaminants and avoid the use of harsh chemicals and physical treatments. However, special care must be employed to ensure that the proper remediation system is designed and engineered to optimize clean-up and minimize costs. Unfortunately, not all bioremediation efforts have been successful. In an attempt to develop bioremediation technology from the flask (bench scale) to the field (full-scale design), many scientists and engineers have failed to understand the phenomena that influence bioremediation. Issues such as additional mass transport mechanisms/limitations, the presence of multiple phases, spatial heterogeneities, and unfavorable factors for bacterial growth represent only a few of the phenomena that can limit or complicate biodegradation. Successful bioremediation requires a complete examination of the phenomena that can be observed as the scientist and engineer progress together from the bench to the field. An excellent way to examine these phenomena is by using the conceptual scales of observation: microscale, mesoscale, and macroscale. The microscale represents the level at which chemical/microbial species and reactions can be characterized independently of any transport phenomena. These activities are those occurring at the microbial cell level and generally are the focus of bench level work. The mesoscale is the level at which transport phenomena and system geometry are first apparent, with the exclusion of advective or mixing processes. This scale represents those activities that occur at the pore channel, soil particle or microbial aggregate level. The macroscale is the scale at which you have the ability to discern advective or mixing phenomena. These activities are generally associated on a site level and are the focus of the design engineer. The critical path as bioremediation technology is developed from flask to field is to observe and understand the phenomena that exert influence at each scale of observation so that its effects can be incorporated into the final remediation design.