908 Research Article Received: 21 September 2011 Revised: 4 November 2011 Accepted: 4 November 2011 Published online in Wiley Online Library: 9 January 2012 (wileyonlinelibrary.com) DOI 10.1002/jctb.3698 Effect of coagulant-flocculant reagents on aerobic granular biomass ´ Angeles Val del R´ ıo, * Nicol ´ as Morales, M ´ onica Figueroa, Anuska Mosquera-Corral, Jos ´ e Luis Campos and Ram ´ on M ´ endez Abstract BACKGROUND: Technologies based on aerobic granular biomass are presented as a new alternative application to wastewater treatment due to its advantages in comparison with the conventional activated sludge processes. However, the properties of the aerobic granules can be influenced by the presence of residual amounts of coagulant-flocculant reagents, frequently used as pre-treatment before the biological process. In this work the effect of these compounds on aerobic granular biomass development was tested. RESULTS: The presence of coagulant-flocculant reagents led to a worse biomass retention capacity with a lower VSS concentration compared with a control reactor (4.5 vs. 7.9 g VSS L -1 ) and with a higher SVI (70 vs. 40 mL [g TSS] -1 ) and diameter (5.0 vs. 2.3 mm). These reagents also caused a decrease in the maximum oxygen consumption rate, but the removal efficiencies of organic matter (90%) and nitrogen (60%) achieved were similar to those in the control reactor. CONCLUSION: The continuous presence of residual levels of coagulant-flocculant reagents from the pre-treatment unit negatively affected the formation process and the physical properties of the aerobic granules; however, the removal of organic matter and nitrogen were not affected. c  2012 Society of Chemical Industry Keywords: aerobic granule; coagulant; flocculant; SOUR; organic matter; nitrogen INTRODUCTION Technologies based on aerobic granular sludge are a promising option for application to wastewater treatment. 1,2 Advantages over the conventional activated sludge systems rely on the capacity to treat higher loads, to achieve better removal efficiencies, to carry out simultaneous elimination of organic matter, nitrogen and phosphorus, 3 and to produce biomass with better settleability properties and low sludge production. Despite all the advantages of aerobic granulation, the development of this technology is recent and research at laboratory scale has been focused on the establishment of optimal operational parameters such as the use of sequencing batch reactors (SBRs), feeding strategy (feast/famine regime), reactor design (large high/diameter ratio), low settling time, aeration intensity (high hydrodynamic shear force), control of the dissolved oxygen concentration, type of substrate, etc. In this sense the study of different types of substrates is important to determine the usefulness of aerobic granulation. Many studies have been performed with synthetic 3–5 and industrial wastewater. 6–10 The effect of different types of toxic compounds, such as phenol and pyridine, as well as the presence of heavy metals and dyes have also been tested. 11,12 However, the presence of coagulant-flocculant reagents, commonly employed in the wastewater treatment plants (WWTPs), has not been studied. During wastewater treatment the use of a pre-treatment before the biological process involving the addition of reagents such as coagulants and flocculants is very common to separate fats and solids. A residual amount of these reagents remains in the supernatant and goes to the biological treatment process, affecting its performance. The presence of coagulant-flocculant reagents in activated sludge systems can prevent the formation of biological foam and the proliferation of filamentous micro- organisms, 13 improve the sludge settling properties 14 and protect membranes from fouling, 15 but can also have negative effects on biomass activity. 14,16 Although there are not specific studies about the effect of these reagents on the formation and properties of the aerobic granular biomass, some studies with cations, such as Ca +2 17 and Mg +2 , 18 show that their presence favour the formation of aerobic granular biomass due to the fact that they act as a bridge to bind negatively charged groups present on bacterial surface and/or extracellular polysaccharide molecules to adhere individual bacteria to each other. 19 So the residual levels of coagulant-flocculant reagents (normally cationic salts) could initially promote aggregation of the biomass, but the long time effect is not known. For this reason, the objective of this work was to study the effect of a residual concentration of coagulant-flocculant reagents on an aerobic granular system, with special attention to the formation ∗ Correspondence to: ´ Angeles Val del R´ ıo, Department of Chemical Engineering, School of Engineering, University of Santiago de Compostela. E-15782. Santiago de Compostela, Spain. E-mail: mangeles.val@usc.es Department of Chemical Engineering, School of Engineering, University of Santiago de Compostela. E-15782. Santiago de Compostela, Spain J Chem Technol Biotechnol 2012; 87: 908–913 www.soci.org c  2012 Society of Chemical Industry