CHARACTERIZATION OF POLYLACTIC ACID COLLOIDS FOR IN SITU BIOREMEDIATION

Westbrook, Ashley N.

Idaho National Laboratory

关键词: Chemical Wastes;    Lactic Acid;    Solvents;    Waste Disposal Acid;    Organic Solvents;   

DOI  :  10.2172/910733
RP-ID  :  INEEL/EXT-03-00954
RP-ID  :  DE-AC07-99ID-13727
RP-ID  :  910733

美国|英语

来源: UNT Digital Library

【 摘 要 】

Groundwater contamination is a widespread problem. As human activities generate chemical wastes, we seek quick, yet not always environmentally friendly, ways to dispose of them. Often, chemicals are dumped into waste containers and buried. Unfortunately, these chemicals may spill or leak, seep deeper into the ground, and eventually reach groundwater. Chlorinated organic solvents such as trichloroethene, tetrachloroethane, and chloroform are common contaminants in groundwater [1]. These solvents originate from chemical spills, tank leaks, and waste disposal practices [2]. Such contaminants are harmful to humans, and need to be removed to restore clean groundwater. There are two types of methods to clean chemically contaminated soil and groundwater: ex situ and in situ. Both types have advantages and disadvantages. In situ remediation avoids the cost of removing the contaminated material and has a lower risk of worker exposure to the contaminants. One in situ technique that shows promise is remediation, which uses microorganisms to anaerobically degrade contaminants. In bioremediation in situ, the microorganisms that are already present in the ground utilize nutrients that are injected into the ground to metabolize the contaminants into nonhazardous materials. The nutrients serve as a carbon source for the microbes. Though this method has been used with some success, there have been problems with too rapid release of nutrients to the microbes. In these cases, the microbes multiplied too rapidly and caused biofouling. This can occur when the nutrient content of the bioremediation solution is too high, as when lactate or lactic acid is the nutrient. Lactic acid is typically produced in carbohydrate matter by fermentation, and is used mainly in the food and pharmaceutical industries [3]. Because it has been found difficult to uniformly distribute lactate solutions in a contaminated area due to biofouling, it was suggested that polylactic acid, in colloidal form, be used instead. Polylactic acid (PLA) is a polymer of lactic acid, C3H6O3 [3]. PLA is used in medicine and agriculture. In medicine, PLA is used in sutures because it degrades within the body after the incision has healed. In agriculture, PLA is used in combination with polyglycolic acid for the release of chemicals [4]. We expect PLA to degrade in the ground at a rate that allows bioremediation to occur as intended. Currently, bioremediation of chlorinated solvents involves injecting nutrient containing solvents into the ground to induce the expected activity of the microbes. The solution must have a proper amount of nutrients for the microbes to metabolize so that they can continue to degrade the contaminants. If too much nutrient is available, and the microbes multiply too fast and clog the injection point, the solution may not reach the area where the contaminants are. One way to slowly release the nutrients for bioremediation is to package them as colloids. Colloids are particles that are less than one micrometer in size, with surface chemical properties that allow them to remain suspended in water and, therefore, to travel with water. Our research addresses the problem of packaging nutrients as colloids to support bioremediation.