Performance of high-loaded ANAMMOX UASB reactors containing granular sludge Chong-Jian Tang a , Ping Zheng a, *, Cai-Hua Wang a , Qaisar Mahmood b , Ji-Qiang Zhang a , Xiao-Guang Chen a , Lei Zhang a , Jian-Wei Chen a a Department of Environmental Engineering, Zhejiang University, Hangzhou 310029, China b Department of Environmental Sciences, COMSATS University, Abbottabad, Pakistan article info Article history: Received 1 November 2009 Received in revised form 28 May 2010 Accepted 10 August 2010 Available online 17 August 2010 Keywords: ANAMMOX Granular characteristics Process performance UASB reactor abstract The performance of high-loaded anaerobic ammonium oxidizing (ANAMMOX) upflow anaerobic sludge bed (UASB) reactors was investigated. Two ANAMMOX reactors (R1 with and R2 without effluent recycling, respectively) were fed with relatively low nitrite concentration of 240 mg-N L 1 with subsequent progressive increase in the nitrogen loading rate (NLR) by shortening the hydraulic retention time (HRT) till the end of the experiment. A super high-rate performance with nitrogen removal rate (NRR) of 74.3e76.7 kg-N m 3 day 1 was accomplished in the lab-scale ANAMMOX UASB reactors, which was 3 times of the highest reported value. The biomass concentrations in the reactors were as high as 42.0e57.7 g-VSS L 1 with the specific ANAMMOX activity (SAA) approaching to 5.6 kg-N kg-VSS 1 day 1 . The high SAA and high biomass concentration were regarded as the key factors for the super high-rate performance. ANAMMOX granules were observed in the reactors with settling velocities of 73e88 m h 1 . The ANAMMOX granules were found to contain a plenty of extracellular polymers (ECPs) such as 71.8e112.1 mg g-VSS 1 of polysaccharides (PS) and 164.4e298.2 mg g-VSS 1 of proteins (PN). High content of hemachrome (6.8e10.3 mmol g-VSS 1 ) was detected in the ANAMMOX granules, which is supposed to be attributed to their unique carmine color. ª 2010 Elsevier Ltd. All rights reserved. 1. Introduction Anaerobic ammonium oxidation (ANAMMOX) is a promising biotechnology for the treatment of ammonium-rich waste- water (van der Star et al., 2007; Joss et al., 2009). Under anoxic conditions, the ANAMMOX bacteria accomplish autotrophic ammonium oxidation to dinitrogen gas employing nitrite as an electron acceptor (Strous et al., 1998). It offers several advan- tages over conventional nitrification-denitrification systems including higher nitrogen removal rate, lower operational cost and less space requirement (Jetten et al., 2005; van der Star et al., 2007; Joss et al., 2009). Combined with single reactor high activity ammonium removal over nitrite (SHARON) process in which half of ammonium is converted to nitrite, the first full-scale ANAMMOX process (70 m 3 ) was applied to treat sludge dewatering effluents in Rotterdam, The Netherlands in 2002 (van Dongen et al., 2001; van der Star et al., 2007). It stably operated achieving nitrogen removal rate (NRR) up to 9.5 kg-N m 3 day 1 (van der Star et al., 2007). High-rate is one of the prime objectives for ANAMMOX process. The NRR of conventional nitrogen removal biotech- nologies was less than 0.5 kg-N m 3 day 1 (Jin et al., 2008); while for ANAMMOX process, it was higher than 5 kg- Nm 3 day 1 as obtained by a number of researchers using different reactors such as upflow biofilter, upflow anaerobic sludge blanket (UASB) reactor and gas-lift reactor (Sliekers * Corresponding author. Tel./fax: þ86 571 86971709. E-mail addresses: chjtangzju@yahoo.com.cn (C.-J. Tang), pzheng@zju.edu.cn (P. Zheng). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres water research 45 (2011) 135 e144 0043-1354/$ e see front matter ª 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2010.08.018