Nitrogen removal in moving bed sequencing batch reactor using polyurethane foam cubes of various sizes as carrier materials Jun-Wei Lim, Chye-Eng Seng ⇑ , Poh-Eng Lim, Si-Ling Ng, Amat-Ngilmi Ahmad Sujari School of Chemical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia article info Article history: Received 31 May 2011 Received in revised form 29 July 2011 Accepted 2 August 2011 Available online 12 August 2011 Keywords: Moving bed sequencing batch reactor Total nitrogen removal Polyurethane foam Simultaneous nitrification and denitrification abstract The performance of moving bed sequencing batch reactors (MBSBRs) added with 8 % (v/v) of polyure- thane (PU) foam cubes as carrier media in nitrogen removal was investigated in treating low COD/N wastewater. The results indicate that MBSBR with 8-mL cubes achieved the highest total nitrogen (TN) removal efficiency of 37% during the aeration period, followed by 31%, 24% and 19 % for MBSBRs with 27-, 64- and 125-mL cubes, respectively. The increased TN removal in MBSBRs was mainly due to simul- taneous nitrification and denitrification (SND) process which was verified by batch studies. The relatively lower TN removal in MBSBR with larger PU foam cubes was attributed to the observation that larger PU foam cubes were not fully attached by biomass. Higher concentrations of 8-mL PU foam cubes in batch reactors yielded higher TN removal. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Nitrogen is widely found in wastewater streams, including mu- nicipal, industrial and agricultural wastewaters. Nitrogen removal can be achieved by nitrification under aerobic conditions and deni- trification under anaerobic conditions. Among various biological treatment systems for nitrogen removal, sequencing batch reactor (SBR) systems possess many advantages including lower opera- tional costs and less bulking. In addition, the cycle format can be flexibly configured to combine nitrification and denitrification phases in one reactor; thus, permitting the building of small treat- ment plant (Louzeiro et al., 2002; Kargi and Uygur, 2003; Yang et al., 2010). Over the years, many efforts have been made to mod- ify the SBR system to improve the performance. Among others, the moving bed sequencing batch reactor (MBSBR) which incorporates both suspended-growth and attached-growth processes has at- tracted much interest among researchers in the field of wastewater treatment (Sirianuntapiboon and Yommee, 2006; Chen et al., 2008; Goh et al., 2009; Guo et al., 2010). Three different type of support media, namely Kaldnes (poly- ethylene media), Liapor (ceramic media) and Linpor (plastic media with high porosity) were studied in nitrogen removal under sequencing batch operation (Valdivia et al., 2007). The results showed that the reactor packed with Linpor performed better in chemical oxygen demand (COD) and ammonium-nitrogen ðNH þ 4  NÞ removal with organic loading rate over 3.0 g COD/ m 3 day. Polyurethane (PU) foam belongs to the Linpor type of sup- port media which has a high porosity and is an ideal medium for biomass immobilization. Besides, it has good mechanical strength and is relatively low cost (Golla et al., 1994; Chu and Wang, 2011). Nitrogen removal through simultaneous nitrification and deni- trification (SND) process had been investigated in the previous studies by using various systems (Kotlar et al., 1996; Daniel et al., 2009; Chu and Wang, 2011). The SND process has generated much interest due to its potential to reduce the operational period in SBR system, resulting in the reduction of operation cost and time. The oxygen concentration and the availability of carbon source for denitrification were found to be the important parame- ters for the commencement of SND (Pochana and Keller, 1999). Previous studies had demonstrated the occurrence of decreasing dissolved oxygen (DO) gradient within the inner layer of biofilm and also deep inside the PU foam (Morper, 1994; Guo et al., 2010). Therefore, the creation of an anoxic condition allowed nitro- gen removal via the SND process. Denitrification process will be inhibited due to the lack of carbon source especially when treating wastewater with low COD/N ratio. In some studies, biodegradable carrier materials were used not only to act as the biofilm carriers but also as an external carbon source for the denitrifiers (Walters et al., 2009; Chu and Wang, 2011). However, replacement of used biodegradable materials is required and therefore this leads to high operating cost. In the study of Guo et al. (2010), different sizes of inert PU foam were used as the carrier material and SND was ob- served in the anoxic zone of the PU foam. The occurrence of the SND without the addition of the external carbon source can be explained by the possibility of carbon storage in the deeper biofilm 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.08.014 ⇑ Corresponding author. Tel.: +60 4 6533546/6574854. E-mail address: ceseng@usm.my (C.-E. Seng). Bioresource Technology 102 (2011) 9876–9883 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech