Polylactate release compounds and methods of using same

The current invention provides for a household of novel compositions to function as substrates that release hydroxy acid slowly over time. Preferably the hydroxy acid is an .alpha. -hydroxy acid, more preferably it’s lactic acid. The compositions are preferably made by reaction of poly(lactic acid) with multifunctional alcohols. Also disclosed are formulations based on the compounds and methods of use for both the compositions and the formulas. The preferred use of the compositions and formulations of the present invention is for bioremediation purposes wherein they provide a time-release supply of lactic acid to support the development and reductive activity of microbes within a system or medium, such as an aquifer, bioreactorand soiland industrial process, wastestream, body of water, river also. The microbes destroy or inactivate chemicals that are capable of being reduced, such as nitrogen-containing organic chemicals, oxygen-containing natural compounds, polyaromatic hydrocarbons, and halogen-containing organic chemicals.

 

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BACKGROUND

 

 
The present invention involves compounds that discharge hydroxy acids gradually over time preferably .alpha. -malic acids. Such chemicals can serve as a time-release source of lactic acid for biodegradation of chemical compounds in a variety of media,such as soils, aquifers, bioreactors, wastestreams, industrial processes, and other methods. The chemicals may also be the basis of formulations that provide a time-release source of lactic acid and other materials and chemicals that stimulategrowth of microbes and facilitate bioremediation. The lactic acid, that is itself a nutrient for microbes, is broken down to form other chemicals that provide both additional nutrients and a source of electrons to support the parasitic biodegradationof chemical compounds, preferably halogenated hydrocarbons.
 

 
Halogenated hydrocarbons are compounds composed of hydrogen and carbon with a minumum of one hydrogen substituted by a halogen atom (e.g. Cl, Br, or F). Halogenated hydrocarbons are used for several functions, such as solvents, pesticides, anddegreasers. Degreasing products have widespread use in several industries, such as dry cleaning, microelectronics, and equipment upkeep. Some of the most frequent halogenated hydrocarbons are methylene chloride, chloroform, carbon tetrachloride,tetrachloroethane (TCA), tetrachloroethene (PCE), trichloroethene (TCE), dichloroethene (DCE), and vinyl chloride (VC). Such compounds are generally called”chlorinated hydrocarbons” or”chlorinated solvents.”
 

 
Chlorinated hydrocarbons have been widely used for several decades. This use, in addition to improper storage and handling, has resulted in extensive soil and groundwater contamination, and such solvents are among the most widespread groundwatercontaminants from the USA today. Contamination of groundwater by chlorinated hydrocarbons is an environmental concern since these chemicals have proven toxic and carcinogenic effects.
 

 
1 common technique for decontaminating aquifers that’s in current use is the pump-and-treat technique. As practiced, this process utilizes a set of extraction wells drilled into a contaminated aquifer. Contaminated water is drawn through anextraction well, treated to remove or degrade the contaminant, and then returned to the aquifer through a couple of injection wells or discharged to sewers or other points of non-origin. This technique can be time intensive and cost-prohibitive.
 

 
Recently, attempts have been made to biodegrade chlorinated solvents in-situ utilizing anaerobic bacteria. Many species of anaerobic bacteria used in bioremediation of chlorinated solvents degrade these solvents by reductive dechlorination. Thisreductive process demands a steady supply of an electron donor like hydrogen. Some current research supports the proposition that shipping of hydrogen in a slow, continuous manner is an efficient way to stimulate and maintain organisms that performreductive dechlorination and reduce competition for ambient hydrogen by other organisms. Several methods have been suggested to furnish the hydrogen required for reductive dechlorination: inclusion of short chain amino acids or alcohols; inclusion of sodiumbenzoate (as disclosed in U.S. Pat. No. 5,277,815); inclusion of fats and oils; sparging with hydrogen gas (as disclosed in U.S. Pat. No. 5,602,296); and creating hydrogen gas in-situ by electrochemical reactions or electrolysis (also disclosed inU.S. Pat. No. 5,602,296).
 

 
All of the earlier mentioned methods have serious consequences. Addition of short chain amino acids or alcohols in addition to the addition of simple natural esters or natural salts like sodium benzoate have the difficulty which essentially allof the chemical is released at the same time in the area and is free to flow away from the contaminated area. Thus, frequent addition of the selected compound is needed to keep a decent concentration of this chemical in the polluted area over time. Theconstant injection of high volumes of solutions increase the loudness of the system or aquifer and thereby potentially cause further spread of this contamination. Additional unless special measures have been taken to deoxygenate the water and solutionswhich are injected, the level of oxygen at the system or aquifer increases, thus harming the anaerobic atmosphere which fosters the microbes doing the reduction.
 

 
Sparging with hydrogen requires the installation and application of pipes, manifolds, valves, and other gear and the treatment of large amounts of an extremely flammable and volatile gas under stress. Production of hydrogen gas in-situ by chemicalreaction or electrolysis as revealed in U.S. Pat. No. 5,602,296 isalso, by those inventors’ own entrance, experimental in nature and like sparging suffers from the further restriction because hydrogen gas has very low solubility in water. Last,addition of fats and oils may supply for its slow release of hydrogen, but the method doesn’t offer a mechanism for controlling the amount of hydrogen released. Furthermore, the amount of hydrogen released is very low compared to the burden of fator oil that has to be added.
 

 
One of the most effective substrates to give hydrogen into your biological system is lactic acid. During anaerobic processes the conversion of lactic acid (or lactate salt) to lactic acid (or acetate salt) liberates 2 moles of dihydrogen (fourmoles of elemental hydrogen) for each mole of lactic acid or lactate consumed. ##STR1##
 

 
Thus the process creates both an electron source (hydrogen) and a nutrient source for bacteria.
 

 
A convenient method of delivering lactic acid would be in the kind of an ester. Esters of lactic acid hydrolyze to produce free lactic acid, or lactate salt, depending upon the pH of the solution. ##STR2##
 

 
The hydrolysis reaction may be catalyzed by acid or base, and the alcohol produced may also serve as a nutrient source of surrounding bacteria. The rate of hydrolysis depends upon both the pH and the alcohol with the ester wasformed. Although simple esters of lactic acid, for example ethyl lactate, delay the launch of free lactic acid into alternative, the lactic acid is still released and converted to hydrogen at a very large pace. This rate might be higher than the pace in whichbacteria performing reductive dechlorination can absorb it, and thus either be wasted or used by other germs that compete with all the reductive dechlorinators.
 

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