Biodegradation of hazardous contaminants in soil may lead to complete mineralization and elimination from soil under biological (compatible with life) conditions. Biodegradation-based in situ remediation belongs to the group of green and eco-friendly soft technologies characterized by high efficiency in clean-up, low secondary impacts on the surrounding environment, and low ecological footprint. In spite of biodegradation’s excellent performance, more aggressive technologies using heavy machinery and conditions far from those of nature’s still often get priority. Energy-, material-, water-, and labor-intensive “pump and treat,” “dig and dump” or “dig and treat” technologies are still practiced, even in cases when high risk or economic interest does not justify urgency.

Bioremediation, natural attenuation, and remediation based on biodegradation has long been involved in research and development and thousands of papers have been published in this field and the number of technology demonstrations and patents are also significant. In the practice biodegradation-based in situ soil remediation is less popular due to the lack of knowledge from the engineering side and the lack of trust from the managers and owners. Biodegradation-based natural attenuation has a pioneering role in this field – mainly through the approved spontaneous biodegradation on long-term abandoned sites – proven that the soil biota is capable of cleaning up the groundwater and the soil in many cases and they deserve the support by engineering tools, which is needed to work at maximum efficiency.

Environmental technology verification and sustainability assessment also became a requirement for remediation. Sustainability assessment is applied to remediation both as a prospective evaluation tool in support of decision making and as a retrospective one for the validation of the predictions in technology efficiencies and approval site (soil) quality (see more in Chapter 11). Sustainability assessment clearly presents the advantages and benefits of biodegradation-based in situ technologies in an absolute sense and in comparison to conventional geotechnical and physicochemical solutions. Biodegradation-based soil remediation can be considered as an ecotechnology, because the soil biota, this special community work according to ecological rules and their remedial function is integral part of the global biogeochemical cycles.

This chapter focuses on the following:

Main principles of microbial degradation (of natural petroleum hydrocarbons and xenobiotics);

Some key reactions of common aerobic and anaerobic biotransformation mechanisms;

Major factors influencing the rate of biodegradation, among others bioavailability the main barrier of biodegradation; and, finally,

244CDT technology, the innovation of the authors, is introduced from the laboratory experiments to the field demonstration. CDT is the cyclodextrin-enhanced in situ biore-mediation, a combination of bioventing and periodic flushing using cyclodextrin for bioavailability enhancement. The CDT case used CDT in combination with groundwater extraction to keep water table low (increasing the aerobic zone depths) and preventing contaminated groundwater from escaping from the site.