Short Communication Microbial community analysis using MiSeq sequencing in a novel configuration fluidized bed reactor for effective denitrification Phatchariya Rungkitwatananukul a , Supanee Nomai a , Yuga Hirakata b , Wiboonluk Pungrasmi a,⇑ , Chaiyaporn Puprasert a , Masashi Hatamoto b , Takashi Yamaguchi b a Department of Environmental Engineering, Faculty of Engineering, Chulalongkorn University, Pathumwan, Bangkok 10330, Thailand b Department of Environmental Systems Engineering, Nagaoka University of Technology, 1603-1, Kami-tomioka, Nagaoka, Niigata 940-2188, Japan highlights  A novel fluidized bed reactor can achieve high performance at low HRT of 50 min.  The COD: NO 3  -N ratio of 3 indicated the highest COD and nitrate removal efficiency.  The ratio of COD: NO 3  -N strongly influenced the composition of microbial community. article info Article history: Received 12 July 2016 Received in revised form 5 September 2016 Accepted 12 September 2016 Available online xxxx Keywords: Fluidized bed reactor Denitrification 16S rRNA gene sequencing Low COD to nitrate ratio Microbial community analysis abstract A novel configured fluidized bed reactor (FBR) with granular rubber as the fluidized media was operated without internal recirculation to achieve denitrification. This FBR could operate under a low hydraulic retention time (HRT) of 50 min due to the low rubber media density and absence of recirculation. Synthetic nitrate-rich wastewater with a fixed nitrate (NO 3  -N) concentration and varying COD concen- trations was fed into the FBR. The nitrate removal profile showed a rapid nitrate reduction at the bottom of the reactor with a high performance under the low HRT. Different microbial communities were iden- tified using Illumina Miseq sequencing. The dominant microorganisms belonged to the Beta- and Gamma- proteobacteria classes and played important roles in nitrate reduction. Acidovorax was abundant at low COD: NO 3  -N ratios, while Rhizobium and Zoogloea were dominant at high COD: NO 3  -N ratios. The COD: NO 3  -N ratio strongly influenced the composition of the microbial community including the dom- inant species. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Wastewater containing high levels of nitrogen compounds can cause serioused problems to the environment. During aerobic wastewater treatment, ammonia is easily converted (oxidized) to nitrate and so the effluent can contain a high nitrate concentration and low chemical oxygen demand (COD). The discharge of this nitrate rich water directly into the environment is a major cause of eutrophication. Also, the consumption of water contaminated with over 10 mg L 1 by children under six months old has been reported by the US Environmental Protection Agency (US EPA) to be the cause of blue baby syndrome. Therefore, nitrate reduction prior to discharge is necessary. Effective nitrate treatment systems operating a under low carbon input can serve as alternative options for cost reduction. The fluidized bed reactor (FBR) is a bio- logical wastewater treatment system that has a high potential for denitrification, and several studies have focused on improving the performance of FBRs (Calderon et al., 1996; Kida et al., 1990). The suitable performance of a FBR for anaerobic wastewater treatment without internal recirculation and using granular rubber as the media has been reported (Sirinukulwattana et al., 2013). Rubber was used because of its low density, suitable surface area and non-toxicity allowing for microbial growth on its surface (Park et al., 2006). The FBR used in that study was small, required a low amount of energy, and differed from classical FBRs in terms of its configuration, height and diameter ratio. In our research, a granular rubber FBR without internal recirculation that was oper- ated at the low hydraulic retention time (HRT) of 50 min was uti- lized for denitrification. The COD and nitrate (NO 3  -N) removal profiles at different COD: NO 3  -N ratios was evaluated as the reac- tor efficiency. Glucose was used as a carbon source to assess the http://dx.doi.org/10.1016/j.biortech.2016.09.051 0960-8524/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: wiboonluk.p@chula.ac.th (W. Pungrasmi). Bioresource Technology xxx (2016) xxx–xxx Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech Please cite this article in press as: Rungkitwatananukul, P., et al. Microbial community analysis using MiSeq sequencing in a novel configuration fluidized bed reactor for effective denitrification. Bioresour. Technol. (2016), http://dx.doi.org/10.1016/j.biortech.2016.09.051