Bioaugmentation and Biostimulation: A Paradox Between Laboratory and Field Results

Abstract

In both shaker-flask and mesocosm-scale experiments, a commercial oleophilic bioremediation agent containing biostimulation (nutrients) and bioaugmentation (bacterial inocula) properties was more effective in enhancing oil biodegradation rates than that of no treatment and/or periodic inorganic nutrient addition. However, similar results were not obtained from a subsequent 129-day field trial conducted in a sand beach environment. In this case, periodic additions of inorganic nutrients, with and without the commercial bioremediation agent, enhanced the number of heterotrophic bacteria and microbial respiration rates within the oiled sediments. The commercial product appeared to elevate the number of oil-degrading bacteria within the oiled sediment between days 17 and 89. However, the addition of inorganic nutrients alone, on a periodic basis, was the most effective means of enhancing the extent of oil biodegradation within the residual oil and of reducing sediment toxicity. By retaining residual oil and altering the physical and chemical characteristics of the treated sediment, the oleophilic product suppressed both the rate and extent of oil loss by tidal activity and biodegradation. This is not to say that the use of the product was ineffective in protecting the environment or was detrimental to it; the product does enhance natural biodegradation rates, and it limits the transport of beached oil to more sensitive areas. This study clearly illustrates the complexity associated with the selection of bioremediation agents, the need for improved experimental protocols for evaluating the performance and toxicity of bioremediation agents, and the potential of nutrient enrichment as a bioremediation strategy.

Bioremediation of Oil on Shoreline Environments: Development of Techniques and Guidelines

“…Controlled studies suggest that optimum rates of degradation could be sustained by retaining high (renewable concentrations, approaching 1-2 mg N/L interstitial pore water) but nontoxic, levels of nutrients [8,9]. The advantages of inorganic agricultural fertilizers as bioremediation agents include low cost, availability, and ease of application.…”

“…Despite the successful demonstration of its efficacy during the Exxon Valdez cleanup operations [6,7] and numerous experimental field trials [8,9,56], bioremediation is still a controversial oil spill countermeasure and justification for its application is still assessed on a case by case basis, beginning with feasibility studies.…”

“…[14]. Indeed, the limitations of the shaker flask and mesocosm tests were recently demonstrated [8]. The results of the shaker flask and mesocosm tests with a commercial bioremediation agent (listed in the current National Contingency Plan (NCP) Product Schedule), containing mineral nutrients and nonpathogenic bacteria, were not achieved under field conditions.…”

“…Absolute levels of contamination can vary widely over a site and simple estimates of biodegradation based on sequential samples can be confounded by this heterogeneity, unless large numbers of samples are taken. However, this problem can be resolved by the normalization of data to conserved markers such as hopanes and chrysenes found within the oil [8,9,77,79]. These costly and time-consuming analyses by gas chromatography/mass spectrometry (GC/MS) are necessary to demonstrate effectiveness at a level of precision and accuracy demanded by the scientific community.…”

“…In consideration of this fact, over the last 20 years, numerous bioremediation strategies have been developed for use as an oil spill countermeasure. With the reported success of cleanup operations using bioremediation in Alaska, following the Exxon Valdez oil spill [4][5][6][7], and that of other controlled field trials [8][9][10], bioremediation is now considered as one the most promising oil spill countermeasures [11,12]. However, to be fully recognized as an operational oil-spill response technology, R&D programs are now required to identify its benefits and limitations, and to provide guidance for its application.…”