Biosurfactant-Facilitated Remediation of Metal-Contaminated Soils

Abstract

Bioremediation of metal-contaminated wastestreams has been successfully demonstrated. Normally, whole cells or microbial exopolymers are used to concentrate and/or precipitate metals in the wastestream to aid in metal removal. Analogous remediation of metal-contaminated soils is more complex because microbial cells or large exopolymers do not move freely through the soil. The use of microbially produced surfactants (biosurfactants) is an alternative with potential for remediation of metal-contaminated soils. The distinct advantage of biosurfactants over whole cells or exopolymers is their small size, generally biosurfactant molecular weights are less than 1500. A second advantage is that biosurfactants have a wide variety of chemical structures that may show different metal selectivities and thus, metal removal efficiencies. A review of the literature shows that complexation capacities of several bacterial exopolymers was similar to the complexation capacity of a rhamnolipid biosurfactant produced by Pseudomonas aeruginosa ATCC 9027. -Environ Health Perspect 1 03(Suppl 1): 59-62 (1995)

Developments in Bioremediation of Soils and Sediments Polluted with Metals and Radionuclides – 1. Microbial Processes and Mechanisms Affecting Bioremediation of Metal Contamination and Influencing Metal Toxicity and Transport

“…Nearly 60% of the selenium in the soils (mean original content: 11.4 ppm) was removed in 22 months, and 18-fold enhancement over removal from untreated plots. The time needed to reach the cleanup goal of 4 ppm was estimated to be 2.6 years (Frankenberger Jr. & Karlson 1994a, 1995.…”

“…These particles usually measure less than 50 nm in diameter and are thus expected to avoid filtration effects in most soils. Adsorption may still impede their progress, however (Miller 1995).…”

“…Composed of polar, often phosphate-based ''heads'' and non-polar lipid ''tails'', biosurfactants combine complexation activity with physical sequestration of the complexed ions (Miller, 1995). A ''surfactant,'' or surface-active agent, diminishes the attractive forces among the molecules of a liquid at the liquid's surface.…”

“…most of these are known to possess metal-binding activity. The emulsan of Acinetobacter RAG-1, for example, binds up to 240 lg UO 2 per mg. Other exopolysaccharides produced by Pseudomonas, Arthrobacter and Klebsiella have bound per mg polymer, up to 96 lg uranium, 3.3 lg cadmium and 22 lg copper, respectively (Miller 1995).…”

Biosurfactant Production from n-Paraffins by an Air Isolate Pseudomonas aeruginosa OCD1

“…Microbial remediation of hydrocarbon and crude oil contaminated soils is an emerging technology involving the application of biosurfactants 7,8 . Biosurfactants are also useful in bioremediation of sites contaminated with heavy metals such as uranium, cadmium, lead etc 9 . In the food processing industries, improvement in dough stability, texture, volume and conservation of bakery products is obtained by addition of rhamnolipid 10 .…”