ABSTRACT
In situ biodegradation may be used to treat low-to-intermediate concentrations of organic contaminants in-place without disturbing or displacing the contaminated media. Although this technology has been used to degrade a limited number of inorganics, specifically cyanide and nitrate, in situ biodegradation is not generally employed to degrade inorganics or to treat media contaminated with heavy metals.
During in situ biodegradation, electron acceptors (e.g., oxygen and nitrate), nutrients, and other amendments may be introduced into die soil and ground water to encourage the growth of an indigenous population capable of degrading the contaminants of concern. These supplements are used to control or modify site-specific conditions that impede microbial activity and, thus, the rate and extent of contaminant degradation. Depending on site-specific cleanup goals, in situ biodegradation can be used as the sole treatment technology or in conjunction with other biological, chemical, and physical technologies in a treatment train. In the past, in situ biodegradation has often been used to enhance traditional pump-and-treat technologies by reducing the time needed to achieve aquifer cleanup standards.
One of the advantages of employing an in situ technology is that media transport and excavation requirements are minimized, resulting in both reduced potential for volatile releases and minimized material handling costs. Biological technologies that require the physical displacement of media during treatment (e.g., “land treatment” applications involving excavation for treatment in lined beds or tilling of nonexcavated soils) assume many of the risks and costs associated with ex situ technologies and cannot strictly be considered in situ applications.
As of Fall 1993, in situ biodegradation was being considered or implemented as a component of the remedy at 21 Superfund sites and 38 Resource Conservation and Recovery Act (RCRA), Underground Storage Tank (UST), Toxic Substances Control Act (TSCA), and federal sites with soil, sludge, sediment, or ground-water contamination [1, p. 13 2 ; 2; 3]. This chapter provides information on the technology’s applicability, the types of residuals produced, the latest performance data, the site requirements, the status of the technology, and sources for further information.
