Municipal Wastewater Selection for Microbial Biodiesel Production

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.