Bioremediation limitations

An issue of particular relevance in the context of bioremediation is illustrated by the increased rate of cell death in an established naphthalene-degrading Pseudomonas putida G7 brought about by the substrate (naphthalene) under conditions of oxygen (or combined oxygen and nitrogen) limitation (Ahn et al. 1998). 

The extent of bioremediation of sediments contaminated with PCBs appears to be limited by the association of a significant fraction with organic components of the sediment phase (Harkness et al. 1993). 

The use of higher plants in bioremediation has been discussed (Schnoor et al. 1995 McIntyre and Lewis 1997 Salt et al. 1998). There are, however, important limitations to the use of plants, which must be considered. These include... 

Collectively, these results illustrate the value of this procedure for determining the occurrence of biodegradation and biotransformation in natural environments, and their application to assessing the effectiveness of bioremediation. A number of important limitations should be addressed. 

On the basis of these limitations, a cautious view of the effectiveness of bioremediation of PAHs seems justified, and they should be taken into account in the design and strategy of bioremediation. 

The prognosis for bioremediation of residues containing polychlorinated anilines and their impurities is rather discouraging. Important factors include (a) limited biodegradability, (b) restricted bioavailability, and (c) the possible formation of oligomeric coupling products. 

The application of deuterated toluene in assessing anaerobic biodegradation (Fischer et al. 2006) has already been noted in Chapter 6, Part 1. A review (Lovley 1997) has summarized the various strategies and suggests that uncertainties, particularly in the bioremediation of benzene, can only be resolved by greater emphasis on field-oriented studies, and a better understanding of the reactions involved and the factors that limit the rates of degradation. 

Bioremediation also has its limitations. Some chemicals are not amenable to biodegradation, for instance, heavy metals, radionuclides, and some chlorinated compounds. In some cases, the microbial metabolism of the contaminants may produce toxic metabolites. Bioremediation is a scientifically intensive procedure that must be tailored to site-specific conditions, and usually requires treatability studies to be conducted on a small scale before the actual cleanup of a site.13 The treatability procedure is important, as it establishes the extent of degradation and evaluates the potential use of a selected microorganism for bioremediation. A precise estimate on vessel size or area involved, speed of reaction, and economics can therefore be determined at the laboratory stage. 

In nature, the ability of organisms to convert contaminants to both simpler and more complex molecules is very diverse. In light of our current limited ability to measure and control biochemical pathways in complex environments, favorable or unfavorable biochemical conversions are evaluated in terms of whether individual or groups of parent compounds are removed, whether increased toxicity is a result of the bioremediation process, and sometimes whether the elements in the parent compound are converted to measurable metabolites. These biochemical activities can be controlled in an in situ operation when one can control and optimize the conditions to achieve a desirable result. 

Boopathy, R., Factors limiting bioremediation technologies, Biores. Technol., 74, 63-67, 2000. 

Most contaminations of aquifers are a result of material being released above the saturated zone. The contaminant pumping method is limited to the cleanup of the saturated zone. Contaminants in the unsaturated zone can still be a source of future contamination. In situ bioremediation techniques can also be designed to clean up the unsaturated zone simultaneously. 

Nutrients—Nutrients, such as nitrogen and phosphorus and other trace elements, are necessary for cell growth because they are key biological building blocks.52,53 Addition of nutrients as a supplement helps ensure that concentrations of nutrients do not become a limiting factor for bioremediation. 

Successful field-scale applications of engineered bioremediation systems have been limited to the aerobic pathway, as opposed to the anaerobic pathway. The advantages of the aerobic pathway include the following ... 

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