Research Article Received: 12 March 2014 Revised: 10 March 2014 Accepted article published: 14 March 2014 Published online in Wiley Online Library: (wileyonlinelibrary.com) DOI 10.1002/jctb.4377 Inhibition of anaerobic ammonium oxidation by heavy metals Guangbin Li, * Daniel Puyol, Jose Maria Carvajal-Arroyo, Reyes Sierra-Alvarez and Jim A. Field Abstract BACKGROUND: Anaerobic ammonium oxidation (anammox) is a promising approach for removing nitrogen from landfill leachates and other nitrogen-laden wastewater. Although heavy metals, which are known for their microbial toxicity, are commonly present in those wastewater streams information on their inhibitory impact on anammox activity is still limited. The main aim of this study is to investigate the inhibitory effects of six common metal ions (Cu 2+ , Cd 2+ , Ni 2+ , Zn 2+ , Pb 2+ , and molybdate) on anammox activity. RESULTS: The soluble concentrations of cationic metals decreased due to precipitation reactions. Cu, Zn, Cd, and Ni were the most toxic metals with 50% inhibiting soluble concentrations of 4.2, 7.6, 11.2, and 48.6 mg L -1 , respectively. Molybdate and Pb 2+ were not or only moderately inhibitory at the highest soluble concentrations tested (22.7 mg Mo L -1 and 6.0 mg Pb L -1 , respectively). A noncompetitive inhibition model successfully described the relationship between microbial inhibition and metal concentrations for all tested metals except for Pb. CONCLUSION: Cu, Zn and Cd were the most toxic heavy metals for anammox bacteria. The soluble concentration of these heavy metals needs to be monitored carefully before applying anammox processes. © 2014 Society of Chemical Industry Supporting information may be found in the online version of this article. Keywords: anammox; copper; zinc; nickel; cadmium; lead INTRODUCTION Anaerobic ammonium oxidation (anammox) is a chemolithoau- totrophic biological process in which ammonium (NH 4 + ) is oxi- dized to N 2 gas using nitrite (NO 2 - ) as the electron acceptor: 1,2 NH + 4 + 1.32NO - 2 + 0.066CO 2 + 0.13H + → 1.02N 2 + 0.26NO - 3 + 2.03H 2 O + 0.066CH 2 O 0.5 N 0.15 (1) To date, five genera, i.e. ‘Kuenenia’, ‘Brocadia’, ‘Anammoxoglobus’, ‘Jettenia’, and ‘Scalindua’, have been reported as anammox can- didates, and all of them are within the phylum Planctomycetes. 3 The anammox process has a remarkable potential for treating ammonia-rich wastewater with low organic matter composition owing to several advantages, such as no requirements for oxy- gen and exogenous electron donor, low sludge production, and the feasibility of treating high nitrogen loading rates. 1,4 When applied together with other pretreatment processes to degrade organic matter and/or satisfy the process requirement for nitrite by nitritation, the anammox process could be used to treat a vari- ety of nitrogen-rich streams such as landfill leachate, sludge cen- trate, semiconductor effluents, wastewater from the production of nitrogenous fertilizers, and piggery wastewater, among others. Elevated concentrations of heavy metals (HMs), including diva- lent copper (Cu), zinc (Zn), nickel (Ni), cadmium (Cd) and lead (Pb), are generally found in municipal landfill leachates. Figure 1 sum- marizes the results of an extensive literature review performed in this study to determine the typical concentration ranges at which HMs are detected in landfill leachates. 5 – 13 This survey con- sidered literature data on the composition of leachates in 13 dif- ferent municipal landfills located in 11 different countries. The figure shows that high concentrations of toxic metals such as Pb 2+ , Zn 2+ and Ni 2+ are often detected in municipal waste landfill leachates. High concentrations of HMs are also commonly present in other nitrogen-rich effluents such as centrates from anaerobi- cally digested sludge, 14 anaerobically digested piggery- and dairy slurries (e.g. Cu, Zn), 15,16 effluents from the production of nitroge- nous fertilizers (e.g. Zn, Pb, Ni, Cr) 17 as well as semiconductor man- ufacturing wastewater streams (e.g. Cu). 18,19 Investigation of the potential inhibitory impact of these metals on the performance of the anammox process is required to facilitate the application of this innovative process in the treatment of complex wastewaters. Some metals are components of many enzymes or co-enzymes and play a significant role in stimulating the metabolism of microorganisms. 20 As an example, copper and molybde- num are important constituents of enzymes involved in the catabolism of anammox bacteria, such as nitrite reductase 21 and ∗ Correspondence to: Guangbin Li, 1133 E. James E. Rogers Way, Tucson, AZ 85721-001, USA. E-mail: guangbinli@email.arizona.edu Department of Chemical and Environmental Engineering, University of Ari- zona, 1133 E. James E. Rogers Way, Tucson, AZ 85721-001, USA J Chem Technol Biotechnol (2014) www.soci.org © 2014 Society of Chemical Industry