SET2009 - 8 th International Conference on Sustainable Energy Technologies, Aachen, Germany August 31 st to 3 rd September 2009 Page 1 of 6 Municipal Wastewater Selection for Microbial Biodiesel Production Julia M. Valigore 1 , Aisling D. O’Sullivan 1,* , and Peter Gostomski 2 Departments of 1 Civil and Natural Resources Engineering and 2 Chemical and Process Engineering, University of Canterbury, Christchurch, New Zealand ABSTRACT: This research compared the effects of municipal wastewaters (i.e., primary and secondary treated) from the Christchurch Wastewater Treatment Plant (CWTP) in Christchurch, New Zealand (NZ) on microbial (microalgal-bacterial) biomass production, settleability, and quality as biodiesel feedstock. Inoculums consisted of native, mixed cultures from an oxidation pond and an activated sludge process. Growth of settleable biomass was encouraged by recycling settleable solids within laboratory-scale sequencing batch reactors (SBRs) operated using a 24-hr cycle, 8-day hydraulic residence time (HRT), and controlled climate conditions. Generally, biomass concentrations of reactors fed with primary wastewater (i.e., 200/400 mg/L final mean for Cold/Warm conditions) were at least double those of secondary wastewater reactors (i.e., 70/210 mg/L final mean for Cold/Warm conditions) due to greater nutrient loading and microbial growth. Furthermore, primary wastewater reactors demonstrated much greater settling (i.e., 76 vs. 22% on average) indicating more efficient biomass harvesting. Lipid contents and types were comparable for all microbial cultures. The benefits of high carbon and bacterial concentrations in primary wastewater appeared to outweigh any disadvantage of reduced light penetration to microalgae from shading. Keywords: Microalgal-bacterial biomass, activated sludge, wastewater treatment, biodiesel * Corresponding author. tel.: +64 3 364-2252; fax: +64 3 364-2758; email: aisling.osullivan@canterbury.ac.nz. 1. INTRODUCTION Microalgal biomass grown on wastewater has potential for sustainable biofuel production [1, 2]. Although this field has been researched since the 1950s [e.g., 3, 4], this is the first known study to compare genuine municipal wastewaters as a substrate for native microbial (microalgal- bacterial) biomass production. The productivity, settleability, and quality of biomass grown on CWTP wastewaters were examined. 2. MATERIALS AND METHODS 2.1 Experimental Setup Four SBRs were inoculated with a 21 L solution of indigenous microalgae and other microbes sourced from Oxidation Pond 6 (P6) wastewater collected from CWTP. One SBR (designated as AP) was also inoculated with 1.5 g (as total suspended solids [TSS]) of activated sludge as previous studies showed that it improved biomass settleability [5]. Four feed water conditions were examined for each climate regime: tap water control, secondary treated wastewater