Effect of Adsorption on the Biodegradation of Nitrilotriacetate by Chelatobacter heintzii

• Published in: Environmental science & technology 1996-06, Vol.30 (6), p.2057-2065
• Main Authors: Bolton, Harvey, Girvin, Don C
• Format: Article
• Language: English
• Subjects: Acids; Bacteria; Biodegradation of pollutants; Biological and medical sciences; Biotechnology; Chemistry; Environment and pollution; Fundamental and applied biological sciences. Psychology; Industrial applications and implications. Economical aspects; Waste materials
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es9508479

Nitrilotriacetic acid (NTA) is a synthetic chelating agent that was used to decontaminate nuclear reactors and was disposed at Department of Energy waste sites. NTA may influence the mobility and fate of radionuclides in soils and sediments if it is not biodegraded. Because it was unclear how adsorption of NTA would influence its degradation, experiments were conducted in a model system containing gibbsite and Chelatobacter heintzii with 60CoNTA at pH 7 and NTA at pH 6 and 8. The rates of NTA desorption from gibbsite were pH dependent (desorption half-lives at pH 6, 7, and 8 were 80, 16, and 1 h, respectively, while that of Co at pH 7 was 2.5 h for equal molar CoNTA). Degradation rates of NTA in solution by C. heintzii decreased as pH decreased and depended on the dominant form of NTA in solution (e.g., biodegradation rates for HNTA2- > AlOHNTA- > CoNTA-). The degradation of NTA was significantly slower when NTA was adsorbed to gibbsite. This difference was observed at pH 6 and 8 with NTA and at pH 7 with NTA and equal molar cobalt. A coupled process model successfully simulated NTA desorption and degradation at all pHs. Both experimental data and simulations demonstrated that adsorbed NTA was unavailable for biodegradation and that the rate of desorption limited the rate of biodegradation. Only a fraction of the total 60Co (i.e., 4%) was associated with C. heintzii cells after NTA had been degraded in the presence of gibbsite. Therefore, the biodegradation of NTA by microorganisms similar to C. heintzii should not significantly alter 60Co sorption to aluminum oxides or 60Co transport where NTA and 60Co have been co-disposed.