EFFECT OF ADSORPTION ON THE BIODEGRADATION OF NITRILOTRIACETATE BY CHELATOBACTER-HEINTZII

Nitrilotriacetic acid (NTA) is a synthetic chelating agent that was us ed to decontaminate nuclear reactors and was disposed at Department of Energy waste sites. NTA may influence the mobility and fate of radion uclides in soils and sediments if it is not biodegraded. Because it wa s unclear how adsorption of NTA would influence its degradation, exper iments were conducted in a model system containing gibbsite and Chelat obacter heintzii with (60)CoNTA at pH 7 and NTA at pH 6 and 8. The rat es 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 fo r HNTA(2-) > AIOHNTA(-) CoNTA(-)). The degradation of NTA was signific antly slower when NTA was adsorbed to gibbsite. This difference was ob served at pH 6 and 8 with NTA and at pH 7 with NTA and equal molar cob alt. A coupled process model successfully simulated NTA desorption and degradation at all pHs. Both experimental data and simulations demons trated that adsorbed NTA was unavailable for biodegradation and that t he rate of desorption limited the rate of biodegradation. Only a fract ion of the total Co-60 (i.e. 4%) was associated with C, heintzii cells after NTA had been degraded in the presence of gibbsite. Therefore, t he biodegradation of NTA by microorganisms similar to C. heintzii shou ld not significantly alter Co-60 sorption to aluminum oxides or Co-60 transport where NTA and Co-60 have been co-disposed.