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P24BIODEGRADATION OF CHELATING AGENTS USED FOR METAL REMOVAL FROM CONTAMINATED SOILS |
Y. Wang and S.K. Banerji, Department of Civil Engineering,University of Missouri, Columbia, MO 65211 |
Chelating agents such as EDTA NTA, DTPA, etc. have been used widely in a variety of industrial applications. Presently they are being used for remediation of heavy metal-contaminated soils. In these applications the contaminated soils are treated with selected chelating agents to extract the metals from the soil phase to the aqueous phase. The chelating compounds in the aqueous phase can later be recovered for reuse by pH modifications. Then the metals in the aqueous phase can be precipitated for proper disposal The reuse of the recovered chelate depends upon its chemical and biological stability under the test conditions.
The biological stability (biodegradability) of two metal chelates diethylenetrinitropentaacetic acid (DTPA) and N-2-acetamidoiminodiacetic acid (ADA) was evaluated under conditions simulating soil remediation processes. A respirometer was used to determine the biodegradation of these chelates under different conditions. Microorganisms acclimated to DTPA were able to degrade this compound at a slow rate up to a concentration of 1mM both in presence and absence of soil. At higher concentrations of Dl PA ( >1 mM) the degradation was retarded. Presence of lead in conjunction with DTPA at neutral pH values caused some toxicity to the microorganisms. ADA was found to be easily biodegraded by the acclimated microorganisms up to a concentration of 3 mM. However, systems with ADA greater than 3mM showed some growth inhibition. Thus, it appears that DTPA may be a better choice for soil metal remediation than ADA based on its biostability in the soil and aqueous environment. Key words: soil metal remediation, metal chelating agents, biodegradation
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