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In situ biodegradation, the activation of microbial processes capable of destroying contaminants where they are found in the environment, is a biological process that responds rapidly to changing environmental factors. Accordingly, in situ sediment enclosures were used to test the efficacy of selected nutrient formulations to enhance the biodegradation of a waxy crude oil in a low-energy shoreline environment. The addition of soluble inorganic fertilizers (ammonium nitrate and triple superphosphate) and slow-release nutrient formulations (sulfur-coated urea) stimulated microbial activity and prolonged the period of oil degradation, despite a decline in seasonal temperatures. Low temperatures reduced the permeability of the coating on the slow-release fertilizers, effectively suppressing nutrient release. Of the nutrient formulations evaluated, we recommend the application of granular slow-release fertilizers (such as sulfur-coated urea) when the overlying water temperatures are above 15° C, and the application of soluble inorganic fertilizers (such as ammonium nitrate) at lower temperatures. Comprehensive analysis of the experimental results indicate that application protocols for bioremediation (form and type of fertilizer or type and frequency of application), be specifically tailored to account for differences in environmental parameters (including oil characteristics) at each contaminated site.

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A new pyrolysis model was developed to predict the individual product (noncondensable volatiles, condensable volatiles, and char) yield for Ecolomondo's industrial waste tire pyrolysis process. This novel predictive kinetics-based model couples product selectivity data obtained from thermogravimetric analysis experiments to a global single-step decomposition reaction term to reproduce the nonlinear relationship between product selectivity and temperature. A transient energy balance based on a lumped capacitance method was also used to calculate the tire shred temperature using the rotary drum wall temperature as an input. The kinetics model was compared to experimental oil production data from the industrial process as well as existing models in the literature. It is shown that the model can successfully predict the oil production of the industrial process and the model accuracy is greater for smooth operating conditions. On the other hand, other pyrolysis models from the literature failed to accurately predict the oil production.

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.

The effects of inorganic (ammonium nitrate and triple superphosphate) and organic (fish bone-meal) fertilizers on the biodegradation rates of Venture condensate within a sand-beach environment were assessed over 333 days. Field results showed that the organic fertilizer stimulated microbial growth and metabolic activity to the greatest extent. However, based on chemical analysis of residual oil concentrations and composition, the application of inorganic fertilizers was the superior bioremediation strategy. This paradox between microbiological and chemical results was attributed to the selective growth of different bacterial populations, the preferential use of components within the organic fertilizer over oil by the indigenous microflora, and the production of toxic metabolic by-products from the degradation of the organic fertilizer.

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