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Anaerobic Digestion of Whole and Lipid-Extracted Algal Biomass from Four Industrial Strains — Determination of Important Methane and Nutrient Information

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  131618699,  2013 Kansas City, Missouri, July 21 - July 24, 2013. (doi: http://dx.doi.org/10.13031/aim.20131618699) @2013
Authors:   Craig Frear, Baisuo Zhao, Jingwei Ma, Quanbao Zhao
Keywords:   Algae anaerobic digestion biorefinery nutrients bio-methane.

Abstract. Anaerobic digestion (AD) is a robust technology for converting organic wastes into biogas and nutrient-rich effluents. Application to algal biomass residues has often been proposed, but relatively few data are available. The National Renewable Energy Laboratory (NREL) and Washington State University (WSU) have partnered on a DOE-funded study of AD in the context of an algal biorefinery. Project goals include: 1) measuring and optimizing methane/biogas productivities and other parameters for a range of industrial species at various scales, 2) understanding the fate of nutrients and the potential for nutrient recycle, and 3) assessing the impacts on process economics and life cycle. Experiments have been conducted on five industrial strains. Both whole cells and solvent-extracted biomass have been digested using a variety of operating conditions (organic loading rates, inoculum type and ratio, hydraulic retention times, etc.) and scales (250 mL batch and 5 L continuous). Specific methane productivities under batch conditions (at 10 grams volatile solids (VS)/L liquid loading) for non-lipid extracted biomass were quite good (0.34-0.60 m3 CH4/kg VS) and exhibited no signs of ammonia or C/N ratio inhibition when digested at high inoculum:substrate (≥1:1). Some species experienced particularly strong digestion inhibition at low inoculum loading and performance appeared related to lipid:protein ratios. Similar productivities, methane concentrations (64-74%), and degree of biodegradability (58-65%) have been seen during preliminary larger-scale, continuous digestion. Specific methane productivities for suitably extracted biomass ranged from 0.30-0.38 m3 CH4/kg VS, at times showing productivities rivaling their lipid containing counterparts but with reduced total biogas.

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