Biochemical Engineering Journal 79 (2013) 153–161 Contents lists available at ScienceDirect Biochemical Engineering Journal jou rnal h om epage: www.elsevier.com/locate/bej Regular Article Physiological characteristics of predominant ammonia-oxidizing bacteria enriched from bioreactors with different influent supply regimes Akihiko Terada a,∗ , Sho Sugawara a , Tomoko Yamamoto a , Sheng Zhou a,1 , Keisuke Koba b , Masaaki Hosomi a a Department of Chemical Engineering, Tokyo University of Agriculture and Technology, Naka-cho 2-24-16, Koganei, Tokyo, 184-8588 Japan b Department of Environmental and Natural Resource Sciences, Tokyo University of Agriculture and Technology, Saiwai-cho, Fuchu, Tokyo, 183-8509 Japan a r t i c l e i n f o Article history: Received 27 December 2012 Received in revised form 18 May 2013 Accepted 28 July 2013 Available online 4 August 2013 Keywords: Ammonia-oxidizing bacteria Biokinetic parameters Halophilic and halotolerant Nitrosomonas spp. Nitritation Nitrosospira spp. a b s t r a c t Two acclimatized biomasses exposed to ammonium (NH 4 + ) concentration of 600 mg N L -1 , one from a completely stirred tank reactor (CSTR), the other from a sequencing batch reactor (SBR), were assayed for nitritation performance, predominant nitrifying bacterial population and nitrous oxide (N 2 O) production. By virtue of fluctuating and constant NH 4 + concentrations respectively, the SBR and CSTR wastewater supply regimes were hypothesized to support different predominant ammonia-oxidizing bacteria (AOB) exhibiting distinct biokinetic properties. Nitritation efficiency (NO 2 - -N/NO 2+3 - -N) was higher in the SBR (89%) than the CSTR (30%) likely due to free ammonia and dissolved oxygen concentration. Quantita- tive fluorescence in situ hybridization (FISH) analyses revealed that fast-growing (r-strategist) AOB of halophilic and halotolerant Nitrosomonas lineage were more highly enriched in the SBR (76 ± 4.2%) than the CSTR (38 ± 6.0%). The CSTR predominantly enriched slow-growing (K-strategist) AOB Nitrosospira spp. (42 ± 1.9% versus 1.4 ± 0.8% in the SBR). Biokinetic parameter estimation consolidated the FISH result: the maximum growth rate and half-saturation coefficients for NH 4 + were higher in the SBR ( max = 0.92 day, K NH4+ = 28.9 mg N L -1 ) relative to the CSTR ( max = 0.42 day, K NH4+ = 3.47 mg N L -1 ), suggesting that the extent of nitritation may be controlled by choice of wastewater influent operational regime, which itself determines predominant AOB. N 2 O production was a maximum of 25 times higher (10.2 mg N-N 2 O h -1 at 0.5 mg O 2 L -1 ) in CSTR-enriched biomass than in SBR-enriched biomass (0.41 mg N-N 2 O h -1 at 0.5 mg O 2 L -1 ). © 2013 Elsevier B.V. All rights reserved. 1. Introduction Removal of ammonium (NH 4 + ) from wastewater is accom- plished in two consecutive biological reactions, nitrification and denitrification [1]. The rate-limiting nitrification step comprises two successive reactions mediated by two groups of autotrophic bacteria, namely, ammonia-oxidizing (AOB) and nitrite-oxidizing bacteria (NOB). Taking advantage of the physiological differ- ences between AOB and NOB allows for cost-effective nitrogen removal pathways, e.g. nitrification-denitrification via nitrite and partial NH 4 + oxidation to nitrite (nitritation), and anaerobic ammonium oxidation (anammox). These result in reduction of the power requirements for aeration, chemical oxygen demand ∗ Corresponding author. Tel.: +81 42 388 7069; fax: +81 42 388 7731. E-mail address: akte@cc.tuat.ac.jp (A. Terada). 1 Eco-environmental Protection Research Institute, Shanghai Academy of Agri- cultural Sciences, Jinqi Road, Shanghai, China. (COD) and sludge production compared with a traditional nitrification and denitrification processes [2]. Success of these nitrogen removal pathways is heavily reliant on stable nitrita- tion by controlling environmental conditions under which AOB prevail over NOB. This, however, remains an engineering chal- lenge. Several technical approaches exist by which to preferentially enrich AOB over NOB. These approaches are based on the differ- ent ecophysiological properties of the two groups, e.g. temperature and solid retention time (SRT) [3,4], free ammonia (FA) [5,6], inorganic carbon [7] and oxygen [8,9]. However, the stability of long-term NO 2 - accumulation, a requirement of successful nitrita- tion, remains questionable. For instance, it has been reported that NOB become tolerant to FA following long term bioreactor oper- ation under a high FA concentration condition [10]. Nitrobacter, a representative NOB genus with a high growth rate, may out- compete some AOB groups, leading to nitritation failure [9,11,12]. Hence, a robust strategy to attain stable long-term nitritation is of primary importance. 1369-703X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.bej.2013.07.012