E. Katsou et al. / Journal of Water Sustainability 1 (2014) 1-11 1 *Corresponding to: francesco.fatone@univr.it Controlled Sewage Sludge Alkaline Fermentation to Produce Vola- tile Fatty Acids to be Used for Biological Nutrients Removal in WWTPs Evina Katsou 1 , Nicola Frison 2 , Simos Malamis 1 , Francesco Fatone 1* 1 Department of Biotechnology, University of Verona, Strada Le Grazie 15, 37134 Verona, Italy 2 Department of Environmental Sciences, Informatics and / Statistics, University Ca’Foscari of Venice, Dorsoduro 2137, 30121 Venice, Italy ABSTRACT In municipal wastewater treatment plants (WWTPs), the disposal of sewage sludge accounts for 20-50% of capital and operating expenses. Therefore, technologies that can simultaneously reduce sludge and generate carbon source for improving biological nutrients removal are in demand. The application of sewage sludge alkaline fermentation can provide the external carbon source that is required to remove nutrients via nitrite for the separate treatment of the supernatant produced from the anaerobic digestion of sewage sludge. Existing studies on sewage sludge fermentation use caustic soda or other chemicals to achieve the desirable pH for alkaline fermentation; this practice increases the cost. In this work, the anaerobic supernatant produced from sewage sludge was used to adjust the pH in the fermenta- tion reactor, while the impact of temperature (30 ° C and 55 ° C), pH (8-11), retention time (1-8 days) and initial total solids (TS = 4.5 and 6.5%) concentration of sludge was examined. The highest volatile fatty acids (VFAs) concentra- tion was achieved at a retention time of 6 days, sludge TS = 6.5%, pH = 10&11 and temperature of 55 ° C. The addition of pre-aerated anaerobic supernatant achieved similar VFAs as the one of similar pH in which caustic soda adjustment took place. Keywords: Alkaline fermentation; sewage sludge; short-chain fatty acids; nutrients removal 1. INTRODUCTION 1.1 Increasing sewage sludge valorisation The extensive application of anaerobic diges- tion for sewage sludge treatment results in the production of high quantities of anaerobic effluents that must be properly managed within the wastewater treatment plant (WWTP). Such effluents are characterized by high nutrients content, since organic nitrogen and organic phosphorus forms are hydrolyzed during the anaerobic digestion process. The usual practice implemented in WWTPs is to return the anaerobic supernatant to the inlet of the sewage treatment line. Although this liquid stream is a small proportion of influent flow, it increases significantly the nitrogen and phosphorus load (by 15-30%). The separate post-treatment of the anaerobic supernatant can relieve the sewage treatment line from such loads, avoiding N and P overloads. Thus, the appli- cation of innovative bioprocesses that will increase the on-site biological valorisation of wastewater and sewage sludge is a major challenge. Journal of Water Sustainability, Volume 4, Issue 1, March 2014, 1-11 © University of Technology Sydney & Xi’an University of Architecture and Technology