Surfactants bioremediation

Microbial-enhanced oil recovery involves injection of carefully chosen microbes. Subsequent injection of a nutrient is sometimes employed to promote bacterial growth. Molasses is the nutrient of choice owing to its low (ca 100/t) cost. The main nutrient source for the microbes is often the cmde oil in the reservoir. A rapidly growing microbe population can reduce the permeabiHty of thief zones improving volumetric sweep efficiency. Microbes, particularly species of Clostridium and Bacillus, have also been used to produce surfactants, alcohols, solvents, and gases in situ (270). These chemicals improve waterflood oil displacement efficiency (see also Bioremediation (Supplement)). 

Different mechanisms have therefore clearly emerged and it seems premature to draw general conclusions especially in the application of synthetic and natural surfactants to bioremediation, which is discussed in greater detail in Chapter 14. It is important to note, however, that the production of biosurfactants may not be the only mechanism for facilitating the uptake of substrates with... 

The relation between the type and concentration of surfactant and the stimulation of biodegradation is therefore complex, and has not so far been fully resolved (Burd and Ward 1996). There seems to be a consensus, however, that supplementation with surfactants is one of the factors that might enhance bioremediation of some contaminated sites (Walter et al. 1997). Some cardinal issues that are potentially negative include the following (Willumsen et al. 1998) ... 

Boopathy, R. and Manning, J., Surfactant-enhanced bioremediation of soil contaminated with 2,4,6-trinitrotoluene in soil slurry reactors, Water Environ. Res., 71, 119-124, 1999. 

The in situ bioremediation application at this site included injection of a liquid microbial solution into the subsurface through monitoring and injection wells. This solution includes microbes (Pseudomonas, Bacillus, and Corynebacterium), oxygen, emulsifier, surfactant, and nutrients. Five injections were conducted. Over 11.3 m3 (3000 gallons) was injected from February 1999 to September 2000 into approximately 40 wells and 15 Geoprobe injection points. As of September 2000, MTBE levels decreased by 96% (3310-146 pg/L), while benzene decreased by 83% (2571— 435 pg/L), toluene by 66% (24,330-8300 pg/L), and naphthalene by 84% (5377-853 pg/L) xylene levels increased and were above preoperational level as of September 2000. The system will continue to be operated until all target levels have been met. The total cost for the cleanup of this site is USD63,500.34... 

Ghosh, M. M., Robinson, K. G., Yeom, I. T. and Z. Shi, Z. (1994). Bioremediation of PAH- and PCB-contaminated soils using surfactants. In Innovative Solutions for Contaminant Site Management. Water Environment Federation, Specialty Conference Series Proceedings, Alexandria, VA, pp. 663-666. 

Microcat (meaning microbial catalysts) products constitute a bioremediation technology used on wastewaters, sludges, and soils. Microcat products include specialized microbial cultures, nutrients, and surfactants to remediate organic contaminants such as petroleum hydrocarbons. The products used in site remediation include ... 

BioSolve is a commercially available biodegradable surfactant that is used to enhance bioremediation of petroleum hydrocarbons in soil and water. According to the vendor, BioSolve emulsifies and encapsulates petroleum-based products so that they become nonflammable and more readily bioavailable. Bioavailability is the combination substrate availability and substrate transport that allows for the initiation of bioremediation. 

The vendor has provided information for two sites where bioremediation was attempted in combination with BioSolve surfactant in 1995. At the Sycamore Pit site, the total cost of BioSolve surfactant used was 1800 this averages approximately 9.00/yd of soil treated. The total cost of remediation at the site was 7800, approximately 39.00/yd of soil treated. At the Tiner Pit site, the cost of BioSolve surfactant was 4050, approximately 3.08/yd of soil treated. 

To increase the usefulness of bioremediation as an effective field remedial tool, significant investments have been made towards the development of means to remove sorbed PAHs, attack sources of NAPL, and subsequently increase the aqueous solubility/bioavailability, and thus the biodegradability, of targeted compounds. To date, one of the most effective ways to accomplish these tasks involves the use of surface active agents (i.e., surfactants). A variety of synthetic surfactants have been shown effective in increasing the bioavailability of PAHs and other hydrophobic contaminants (Kile Chiou, 1989, 1990 Edwards et al., 1991 Liu et al., 1991). Although the solubilization process is not completely understood, these studies showed that a variety of ionic and nonionic surfactants could significantly increase the water solubility of monitored chemicals. 

Green, G. (1990). The Use of Surfactants in the Bioremediation of Petroleum Contaminated Soils. USA Report No. EPA/101/F-90/013, NTIS Report No. PB90-256546. 

Miller, R.M. (1995b). Surfactant-enhanced bioavailability of slightly soluble organic compounds. In Bioremediation-Science Applications, ed. H. Skipper, pp. 35-54. Madison, WI Soil Society of America. 

Radio frequency heating, 500 Steam stripping, 500 Vacuum extraction, 500 Aeration, 501 Bioremediation, 501 Soil flushing/washing, 502 Surfactant enhancements, 502 Cosolvents, 502 Electrokinetics, 503 Hydraulic and pneumatic fracturing, 503 Treatment walls, 505 Supercritical Water Oxidation, 507 Solid Solution Theory, 202 Solubility products, 48-53 Metal carbonates, 433-434 Metal hydroxides, 429-433 Metal sulfides, 437 Sorption, 167 See Adsorption Specific adsorption, 167 See Chemisorption Stem Layer, 152-154 Sulfate, 261... 

Available data suggest that the supra-CMC inhibitory effect on biodegradation is reversible and not a specific toxic effect. Partial inhibition of microbial degradation of phenanthrene was observed for nonionic surfactants at sub-CMC doses. It is not clear whether these effects result from surfactant interactions with microorganisms or from preferential use of surfactant as substrate or source of carbon. The effects of surfactant monomers and micelles on microbial cell surfaces and constituents, and effects related to preferential substrate utilization and mineralization of degradation products, must be better understood in order to evaluate whether synthetic surfactants may be employed advantageously to enhance bioremediation in soil-water systems. 

A number of different mechanisms have therefore clearly emerged and it seems premature to draw general conclusions especially with respect to the application of these natural surfactants to bioremediation that is discussed in greater detail in Chapter 8, Section 8.2.1. It is important to note that production of biosurfactants may not be the only mechanism for facilitating the uptake of substrates with low water solubility. For a strain of Rhodococcus sp. that did not produce surfactants, the rates of degradation of pyrene dissolved in water in the presence of insoluble, nondegradable 2,2,4,4,6,8,8-heptameth-ylnonane exceeded those predicted for physicochemical transfer from the solvent to the aqueous phase, but could be accounted for on the basis of uptake both from the interface and from the aqueous solution (Bouchez et al. 1997). 

A discussion of factors determining the effectiveness of bioremediation including the effect of complex mixtures of contaminants, the limitation of bioavailability, the value of surfactants, and of nutrients and inoculation (Hughes et al. 1997) ... 

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