We have identified and tested a new colloidal tracer for use in hazardous waste site characterization and other environmental applications. The tracer is primarily composed of the dead ice nucleating active (INA) bacterium Pseudomonas syringae. Assay conditions are simple and based on the observation of the freezing behavior of 10 μl solution volumes. Under specific assay conditions (−5 to −7°C) these drops freeze only if the tracer is present. The results are available within 3 min of sample collection thus, providing near real-time results. The tracer detection limits are in the range of ng/l, it is stable over a pH range of 2–11, and maintains its high activity in the presence of a variety of contaminant compounds. In a simple column experiment this colloid tracer eluted just prior to NaCl with little or no tailing.

BioTreat™, a commercially available nutrient-surfactant compound, was investigated for its ability to solubilize TCE. Potential mechanisms for enhancing biodegradation rates by the use of nutrient-surfactant mixtures are: increased solubilization of TCE into the aqueous phase, and increased nutrients for the bacteria and greater numbers of colony forming units (CFUs). In aqueous systems, no measured solubilization of 0.1 and 1.0 ppm TCE from the headspace into the liquid phase was observed with BioTreat added at concentrations <0.5%. However, at BioTreat concentrations in excess of the CMC (≥0.5%), increased solubilization of TCE was measured. A second question was the nutrient effect of BioTreat on the growth of the TCE-degrading bacterium, Burkholderia cepacia G4 PR1301. The added nutrients provided by BioTreat was evident and lead to increased cell numbers. The effect of BioTreat on the expression of ortho-monooxgenase, the enzyme necessary for TCE degradation by B. cepacia was also investigated. Enzyme expression as detected by a colorimetric assay was inhibited for BioTreat concentrations <0.05%.

To determine if compounds added during trichloroethylene (TCE) degradation could reduce the loss of enzyme activity or increase enzyme recovery, different compounds serving as energy and carbon sources, pH buffers, or free radical scavengers were tested. Formate and formic acid (reducing power and a carbon source), as well as ascorbic acid and citric acid (free radical scavengers) were added during TCE degradation at a concentration of 2 mM. A saturated solution of calcium carbonate was also tested to address pH concerns. In the presence of formate and methane, only calcium carbonate and formic acid had a beneficial effect on enzyme recovery. The calcium carbonate and formic acid both reduced the loss of enzyme activity and resulted in the highest levels of enzyme activity after recovery.

In Mexico, there are several environmental issues which are being addressed under the current governmental legislation. One important issue is restoring sites belonging to Petroleos Mexicanos (PEMEX). PEMEX is a large government owned oil company that regulates and manages the oil reserves. These sites are primarily contaminated with weathered hydrocarbons which are a consequence of extracting millions of barrels of oil. Within the southern regions of Mexico there are sites which were contaminated by activities and spills that have occurred during the past 30 years. PEMEX has taken the leadership in correcting environmental problems and is very concerned about cleaning up the contaminated sites as quickly as possible. The most significant contaminated sites are located to the north of Veracruz and south of Tabasco. These sites areas are close to refineries or locations of oil exploration. The primary category of contaminants are hydrocarbons, among them asphaltens, aromatic and other contaminants. The concentration of the contaminants varies depending on the location of the sites, but it can reach as high as 500,000 ppm. PEMEX has been searching for appropriate, and cost- effective technologies to clean up these sites. Biologically based remediation activities are of primary interest to PEMEX. However, other treatment technologies such as chemical-physical methods, encapsulation and incineration are also being considered. The present report summarizes preliminary experiments that measured the feasibility of bioremediation for a contaminated site in southern Mexico.

In situ bioremediation is a very attractive, safe and efficient method of not only removing, but eliminating hazardous compounds from the environment. However, the quickest and most efficient method of restoring a hazardous waste site would be to link several remediation processes. In situ biodegradation can involve the addition of nutrients, oxygen, electron donors, electron acceptors, organisms or all the above. These amendments can be introduced and coupled to a variety of other technologies such as permeability enhancements, chemical treatments and/or physical processes. In addition to in situ technologies, bioremediation in bioreactors is an efficient tool facilitating mineralization of contaminants. Overall, biodegradation has a significant potential to increase the rate of site restoration and decrease overall costs. 37 refs., 2 figs.

A two-stage biorector system was continuously fed a solution of TCE (concentrations ranging between 0.2 and 20 mg L(-1)) at 2 mL min(-1); the system utilized a mutant (PP358) of the methane oxidizing bacterium Methylosinus trichosporium OB3b for the fortuitous cooxidation of TCE by the enzyme-soluble methane monooxygenase (sMMO). A methane-free environment was maintained in the TCE treatment portion of the reactor (plug-flow columns), minimizing the effects of competitive inhibition between TCE and methane for the sMMO. The reactor was operated in two separate flow configurations, single-pass and crossflow, with TCE removal percentages exceeding 78% (for a TCE feed concentration of 20 mg L(-1)) and 93% (for a TCE feed concentration of 10 mg L(-1)), respectively. A r(max) of 109.4 mg of TCE (g of VS)(-1) d(-1) for a TCE feed concentration of 20 mg L(-1) was obtained, suggesting that high rates of degradation occurred within the reactor. CE-induced toxicity effects occurred at TCE feed concentrations of 10 mg L(-1) and greater, resulting in declines of the biomass concentrations and the enzyme activities. However, the extent of this decline was alleviated by the addition of 0.2 M sodium formate. A model describing the rate of TCE degradation in the plug-flow columns was proposed by Alvarez-Cohen et al. and was modified to incorporate the suboptimal activities of sMMO. The model was adjusted to the data, and an apparent rate constant, K, of 0.041 (dimensionless) was obtained. The effect of the finite transformation capacity term, T-c, in the model was noticeable only at high TCE feed concentrations. The model suggested that cross-flow operation was kinetically favored over single-pass operation due to enhanced TCE to biomass ratios. The model may be used to predict the extent of TCE degradation for a system and may serve as a useful tool for the optimization of flow rates. The optimization may include maximizing the rate of TCE degradation or minimizing the necessary residence time in a methane-starved environment.

Soil column studies were used to evaluate petroleum hydrocarbon (PHC) remediation in soils from Kwajalein Atoll. Treatments included controls, and combinations of water, air, nutrients, and bioaugmentation with indigenous microbes (W, A, N, and M, respectively). Microbial colony forming units (CFU) decreased in the control columns and in treatments without air. Treatments including W + A + N and W + A + N + M exhibited increased CFU. One third of the PHC was removed by water and another third was removed by W + A + N and W + A + N + M treatments. Bioaugmentation with indigenous PHC degraders did not enhance bioremediation. Potential for bioremediation was demonstrated by air, water, and nutrient amendments.