Evaluation of granular sludge for secondary treatment of saline municipal sewage Ben van den Akker a, b, c, * , Katherine Reid a , Kyra Middlemiss a , Joerg Krampe d a Australian Water Quality Centre, SA Water Corporation, Adelaide, 5000 South Australia, Australia b Health and Environment Group, School of the Environment, Flinders University, Bedford Park, 5042 South Australia, Australia c Centre for Water Management and Reuse, School of Natural and Built Environments, University of South Australia, Mawson Lakes, 5095 South Australia, Australia d Institute for Water Quality, Resource and Waste Management, Vienna University of Technology, Karlsplatz,1040 Vienna, Austria article info Article history: Received 5 January 2015 Received in revised form 10 April 2015 Accepted 15 April 2015 Available online Keywords: Granular sludge Salinity COD Nitrous oxide Dissolved oxygen abstract This study examined the impact of chemical oxygen demand (COD) loading and dissolved oxygen (DO) concentration on the stability and performance of granular sludge treating high saline municipal sewage. Under high DO concentrations of 4.0e7.0 mg/L, and COD loading rates of 0.98 and 1.55 kg/m 3 /d, rapid settling granules were established within four weeks of start-up. Under the highest COD load, a reduction in DO lead to the rapid deterioration of the sludge volume index (SVI) and washout of granules due to prolific growth of the filament Thiothrix Type 021N. Conversely, when operated under a lower COD load, a reduction in DO concentration had no adverse impact on the stability of SVI and granules. A decrease in DO also improved nitrogen removal performance, where simultaneous removal of ammo- nium (98%), total nitrogen (86%) and BOD 5 (98%) were achieved when median DO concentrations were between 1.0 and 1.5 mg/L. Phosphate removal was lower than expected, however the level of biological phosphate removal activity observed appeared sufficient to maintain granule stability, even under low DO concentrations. Nitrous oxide emissions were also characterised, which ranged between 2.3 and 6.8% of the total nitrogen load. Our results confirmed that granular sludge is a viable option for the treatment of saline sewage. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, new technologies have been developed to improve the settling properties of activated sludge and the use of granular sludge in sequencing batch reactors (SBRs) is a novel so- lution that has the potential to become industry standard for sec- ondary treatment. Extensive research has shown that the operation of SBRs can be modified to convert slow settling activated sludge flocs into dense microbial granules, which have superior settling properties (Beun et al., 1999; de Bruin et al., 2004; Etterer and Wilderer, 2001). In particular, granular sludge is achieved by employing a short settling phase to select for fast settling biomass, coupled with an anaerobic feed that encourages the development of slow-growing organisms, such as polyphosphate accumulating organisms (PAOs). PAOs convert easily degradable substrates, such as acetate, into microbial storage polymers, thereby gaining a competitive advantage over floc-forming organisms (Bassin et al., 2012; Beun, 2001; Beun et al., 1999; De Kreuk et al., 2005). The potential benefits of a granular sludge system are numerous. Granules have excellent settleability, resulting in a highly clarified effluent and, like biofilms, have an oxygen gradient which facilitates efficient and simultaneous nitrification- denitrification and biological phosphorus removal (Bassin et al., 2012; Pronk et al., 2013). The rapid settling phase enables shorter cycle times, which increase the hydraulic capacity or reduce physical footprint, and the fast settling granules allows the reactor to retain more active biomass than a conventional SBR of the same size (Pronk et al., 2013). To date, granular sludge has been incorporated into several full- scale industrial and municipal WWTPs in Europe, South America and South Africa, however this technology has not yet been utilised at full-scale in Australia. For Australia, granular sludge may offer the * Corresponding author. Australian Water Quality Centre, SA Water Corporation, Adelaide, 5000 South Australia, Australia. E-mail address: ben.vandenakker@sawater.com.au (B. van den Akker). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman http://dx.doi.org/10.1016/j.jenvman.2015.04.027 0301-4797/© 2015 Elsevier Ltd. All rights reserved. Journal of Environmental Management 157 (2015) 139e145