Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres Biodegradation of nitrilotriacetic acid (NTA) and ferric–NTA complex by aerobic microbial granules Y.V. Nancharaiah a , N. Schwarzenbeck b , T.V.K. Mohan a , S.V. Narasimhan a , P.A. Wilderer b , V.P. Venugopalan a,Ã a Water and Steam Chemistry Laboratory, BARC Facilities, Kalpakkam, Tamil Nadu 603102, India b Institute of Water Quality and Waste Management, Technical University of Munich, Am Coulombwall, Garching 85748, Germany article info Article history: Received 25 April 2005 Received in revised form 2 February 2006 Accepted 5 February 2006 Available online 4 April 2006 Keywords: Biodegradation Chelating agent Microbial granules Nitrilotriacetic acid Granulation ABSTRACT Development of mixed-culture microbial granules under aerobic conditions in a sequen- cing batch reactor (SBR), capable of completely degrading a recalcitrant metal chelating agent is reported. In laboratory-scale reactor studies, the microbial granules degraded 2 mM of free nitrilotriacetic acid (NTA) and Fe(III)–NTA completely in 14 and 40h, respectively. Free NTA was degraded at a specific rate of 0.7 mM (g MLSS) 1 h 1 , while Fe(III)–NTA was degraded at a specific rate of 0.37 mM (g MLSS) 1 h 1 . Achievement of significant degradation rates of NTA and ferric–NTA in double-distilled water suggests that the microbial metabolism is not constrained by lack of essential elements. Efficient degrada- tion of recalcitrant synthetic chelating agents by aerobic microbial granules suggests their potential application in a variety of situations where heavy metals or radionuclides are to be co-disposed with metal chelating agents. & 2006 Elsevier Ltd. All rights reserved. 1. Introduction Synthetic chelating agents are used in many industrial applications because of their capability to bind and mask metal ions. Amongst these, nitrilotriacetic acid (NTA) is a synthetic organic metal chelating agent whose metal binding properties are exploited in a wide range of applications. These include detergent, food, pharmaceutical, cosmetic, metal finishing, photographic, textile and paper industries. It is also used as a component in decontamination formulations of nuclear reactors and in nuclear waste processing (Bolton et al., 1996; Witschel and Egli, 2001; White and Knowles, 2003). Chemical decontamination processes use one or a mixture of chelating agents such as ethylenediaminetetraacetic acid (EDTA), NTA, picolinic acid and citric acid. Chelating agents can form very strong complexes with metal ions and radio- nuclides. NTA has found widespread use in conditioning reactor cooling water, as an anticorrosive and scale inhibitor and in cleanup operations (White and Knowles, 2003). Co- disposal of heavy metals or radionuclides along with syn- thetic organic chelating agents creates environmental pro- blems because the latter may promote undesirable displacement of toxic heavy metals/radionuclides away from the primary disposal site (Bolton et al., 1996; Thomas et al., 1998). Therefore, it is desirable to remove the chelating agents from the wastes prior to disposal. However, synthetic chelat- ing agents and their metal complexes are recalcitrant and resist biodegradation; only a few bacterial strains are able to degrade them, albeit at relatively lower rates (White and Knowles, 2003). Studies on microbial degradation of NTA (White and Knowles, 2000, 2003) and other chelating agents (Witschel and Egli, 2001; Reinecke et al., 2000; Joshi-Tope and Francis, 1995) revealed that metal complexation has a significant negative effect on biodegradability of the chelant. ARTICLE IN PRESS 0043-1354/$ - see front matter & 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2006.02.006 Ã Corresponding author. Tel.: +91 44 2748 0203; fax: +91 44 2748 0097. E-mail address: vpv@igcar.gov.in (V.P. Venugopalan). WATER RESEARCH 40 (2006) 1539– 1546