Enhancing aerobic granulation for biological nutrient removal from domestic wastewater M. Coma a,b,⇑ , M. Verawaty a , M. Pijuan a,c , Z. Yuan a , P.L. Bond a a The University of Queensland, Advanced Water Management Centre (AWMC), QLD 4072, Australia b Laboratory of Chemical and Environmental Engineering (LEQUIA-UdG), Institute of the Environment, University of Girona, Campus Montilivi s/n, E-17071 Girona, Spain c Catalan Institute for Water Research, Technological Park of the University of Girona, 17003 Girona, Spain article info Article history: Received 13 July 2011 Received in revised form 1 October 2011 Accepted 3 October 2011 Available online 10 October 2011 Keywords: Aerobic granular sludge Biological nutrient removal Domestic wastewater Nitrite inhibition Seed sludge abstract This study focuses on the enhancement of aerobic granulation and biological nutrient removal mainte- nance treating domestic wastewater. Two sequencing batch reactors (SBRs) were inoculated with either only floccular sludge (100%-floc SBR) or supplemented with 10% crushed granules (90%-floc SBR). Gran- ules developed in both reactors. The 100%-floc SBR achieved 75% of nitrogen and 93% of phosphorus removal at the end of the performance, but some floccular sludge remained in the system. The 90%-floc SBR became fully granulated and finished with 84% and 99% of nitrogen and phosphorus removal, respec- tively. Regarding biological phosphorus removal, nitrite was identified as an inhibitor of the process. Nitrite levels lower than 5 mg N–NO  2 L 1 were used for anoxic phosphate uptake while higher concen- trations inhibited the process. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Some of the main disadvantages in activated sludge wastewater treatment relate to the floccular nature of the sludge, as large areas for reactors and especially settlers are required (Beun et al., 1999). Aerobic granular sludge has been recently developed in laboratory- scale systems. Granules are large suspended biofilms having regu- lar and dense structure with advantageous qualities in comparison to floccular sludge, these include: superior settling properties, high biomass retention, better able to withstand high-strength wastewater and shock loadings, and improved dewatering capabilities (Liu and Tay, 2004). The performance of aerobic granular sludge systems has been assessed in laboratory-scale reactors while treating synthetic wastewater, or more recently to treat industrial wastewater, such as dairy or livestock (de Kreuk and van Loosdrecht, 2006; Lemaire, 2007; Yilmaz et al., 2008). Currently there are very few studies of municipal wastewater treatment by aerobic granules. Some stud- ies have been carried out for nutrient removal treating synthetic wastewater with constituent concentrations that simulate those in domestic sewage (Coma et al., 2010; Li et al., 2007) and others have investigated nutrient removal from real domestic wastewater using acetate fed granules (Liu et al., 2007; Wang et al., 2009). However, aerobic granular sludge development with real low-strength wastewater (such as domestic) has been found unsuitable with long start-up periods when organic loads are lower than 1000 g COD m 3 d 1 (de Kreuk and van Loosdrecht, 2006). Successful COD and nitrogen removal from domestic wastewater by aerobic granules is reported when applying high loads (Liu et al., 2010) and in biofilter granular SBR systems (Di Iaconi et al., 2008; Ramadori et al., 2006). Ni et al. (2009) reported gran- ulation in a pilot-scale reactor for removal of organic matter and ammonium at 600–1000 g COD m 3 d 1 , but neither denitrifica- tion or phosphorus removal was reported. The majority of studies of aerobic granulation focus on organic matter removal while applying complete aerobic conditions. In order to perform both nitrogen and phosphorus removal, anaerobic and anoxic phases are also required. Nitrogen is removed in a two-stage process: oxidation of ammonium to nitrite or nitrate under aerobic conditions (nitrification) and reduction of these compounds to nitrogen gas in the presence of organic matter under anoxic conditions (denitrification). Enhanced biological phospho- rus removal (EBPR) also occurs under alternating conditions; in anaerobic conditions organic matter is taken up by polyphosphate accumulating organisms (PAOs) using the glycolysis of intracellu- lar glycogen and cleavage of polyphosphate to conserve energy and build up intracellular stores of polyhydroxyalkanoates (PHA). As a consequence phosphate is released to the media. During the following aerobic or anoxic period, PAOs use the stored PHA to replenish intracellular pools of glycogen and polyphosphate, effectively removing phosphate from the wastewater (Oehmen 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.10.014 ⇑ Corresponding author at: Laboratory of Chemical and Environmental Engineer- ing (LEQUIA-UdG), Institute of the Environment, University of Girona, Campus Montilivi s/n, E-17071 Girona, Spain. Tel.: +34 972183249; fax: +34 972418150. E-mail address: marta@lequia.udg.cat (M. Coma). Bioresource Technology 103 (2012) 101–108 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech