Treatment of saline wastewater by a sequencing batch reactor with emphasis on aerobic granule formation Ensiyeh Taheri a , Mehdi H. Khiadani (Hajian) a,b,⇑ , Mohammd Mehdi Amin a , Mahnaz Nikaeen a , Akbar Hassanzadeh c a Environment Research Centre, Isfahan University of Medical Sciences, Isfahan, Iran b School of Engineering, Edith Cowan University, WA 6027, Australia c Department of Epidemiology, Isfahan University of Medical Sciences, Isfahan, Iran article info Article history: Received 8 November 2011 Received in revised form 24 January 2012 Accepted 26 January 2012 Available online 6 February 2012 Keywords: Aerobic granule Structure PCR Microbiology abstract The formation and characteristics of aerobic granules in a sequencing batch reactor (SBR), designed to treat saline wastewater, have been investigated in this study. Granule structure was determined using scanning electron microscope (SEM), and polymerase chain reaction (PCR). Granules formed in the reac- tors were grouped into light brown granules and black granules that looked ‘fluffy’. The first group was more dense than the second group and consequently had a higher settling velocity. The densities of the first and the second group were 0.056 and 0.035 g/ml, respectively. While the corresponding settling velocity were 1.35 and 0.97 cm/s, respectively. The kinetic coefficients K s , k d , k and Y in saline substrate (10 g NaCl/l) were estimated to be 195 mg s COD/l, 0.025 g VSS/g VSS d, 2.29 g s COD/g VSS d and 0.45 mg VSS/mg s COD, respectively. Analysis of granules using 16S rDNA sequences showed that the dominant microbial species was Klebsiella oxitoca. Minerals and the protozoan community in saline sub- strate facilitated the formation of granules. It was concluded that the fluffy granules are a variation of the light brown granules which are resistant to salt. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Aerobic granules have advantages over flocs in conventional activated sludge in treatment of wastewater. The microbial struc- ture of aerobic granules is denser and consequently they settle fas- ter. Also they could bear the incoming shocks and are tolerable to medium toxic environment (Adav et al., 2010; Qin et al., 2004; Sun et al., 2006). It is believed that aerobic granulation can become one of the new technologies in wastewater treatment (Ren et al., 2008). Aerobic granulation of sludge is an advanced process that has the potential to become a major biological wastewater treatment tech- nology in degradation and removal of organic material (Sheng et al., 2010). Over the past two decades, aerobic biological granula- tion technology has shown to be useful for the treatment of toxic wastewater, in systems that provide an optimal environment for the formation of aerobic granules (Adav et al., 2009c; Qin et al., 2004). The effect of sedimentation time on granulation in three different sequencing batch reactors (SBR) has shown that lower sedimentation time form granules more successfully (Adav et al., 2009a). In contrast, some studies have shown that parameters such as solids retention time (SRT) does not influence the formation of biological granules (Li et al., 2008). Extracellular polymeric sub- stances (EPS), are important in joining bacteria to form and stabi- lize granules and are a combination of polysaccharides, nucleic acids and lipids (Adav et al., 2008a,b). Various species such as ß and Gammaproteobacterias, Flavobacterium, and Klebsiella oxitoca were found to be dominant in the process of aerobic granulation (Adav et al., 2009a,b; Hung et al., 2011; Li et al., 2008; Liu et al., 2010; Sheng et al., 2010). Formation of aerobic granules in SBR systems has frequently been reported (Muda et al., 2010). This study was designed to treat saline wastewater in a SBR system. Treatment of saline wastewater can be challenging, because of plasmolysation of cells, reduction of biological activities, induced salt stress to microbial species, and inhibition of many enzymes. Despite these, adaptation of activated sludge to salinity is achievable (Lefebvre and Moletta, 2006). It has been reported that salinity does not change kinetic coefficients (Moon et al., 1997). Formation of aerobic granules in biological sys- tems, including treating saline wastewater, is complex topic, par- ticularly as the mechanism of aerobic granulation is unknown (Xia et al., 2010). Structure of anaerobic granules has been studied and no relationship was found between granule formation and bacterial species, morphology and adaptation mechanism (Baloch et al., 2008). Aerobic granule formation via microbial aggregation 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2012.01.164 ⇑ Corresponding author at: School of Engineering, Edith Cowan University, WA 6027, Australia. Tel.: +61 8 6304 5825; fax: +61 8 6304 5811. E-mail addresses: e_taheri_83@yahoo.com (E. Taheri), m.khiadani@ecu.edu.au (M.H. Khiadani (Hajian)), amin@hlth.mui.ac.ir (M.M. Amin), nikaeen@hlth.mui.ac.ir (M. Nikaeen), hassanzadeh@hlth.mui.ac.ir (A. Hassanzadeh). Bioresource Technology 111 (2012) 21–26 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech