Economic and environmental performance of microalgal energy products - A case study exploring circular bioeconomy principles applied to recycled anaerobic digester waste flows.

This study quantifies the financial and environmental impacts of a microalgal bioenergy system that attempts to maximize circular flows by recovering and reusing the carbon, nutrients, and water within the system. The system produces microalgal biomass using liquid digestate of an anaerobic digester that processes 45 metric tons of food waste and generates 28.6 m3 of permeate daily in California, and three energy production scenarios from the biomass are considered: producing biodiesel, electricity, and both. In all scenarios, the resulting energy products delivered only modest reductions in environmental impacts as measured by carbon dioxide equivalent emissions. The carbon intensities (CIs) of biodiesel from this study were 91.0 gCO2e/MJ and 93.3 gCO2e/MJ, which were lower than 94.71 gCO2e/MJ of conventional petroleum diesel, and the CI of electricity from this study was 70.6 gCO2e/MJ, lower than the average electricity grid CI in California (82.92 gCO2e/MJ). The economic analysis results show that generating electricity alone can be profitable, while biodiesel produced via this system is not cost competitive with conventional diesel due to high capital expenses. Thus, generating electricity in lieu of biodiesel appears to be a better option to maximize the use of waste flows and supply lower-carbon energy.

Conversion of Microbial Lipids to Biodiesel and Basic Lab Tests for Analysis of Fuel-Quality Parameters.

This chapter describes lab-scale procedures for the direct conversion of microbial lipids to fatty acid methyl esters (FAMEs) for use as biodiesel fuel. Methods for the gas chromatography analysis of FAME profiles and equations to predict several fuel-quality parameters are detailed herein. This chapter also provides a complete list summarizing each of the fuel quality tests (e.g., sample size and equipment) that are required by ASTM International D6751 regulations for pure biodiesel fuel (B100) or blend stock. Recommendations for the decolorization of microbial lipid sources containing pigments are also included. This resource should provide a guide to basic conversion and characterization of microbial-derived biodiesel fuels and a roadmap for more-detailed testing required to assess commercial feasibility.