A Novel Platform for Algal Biomass Production Using Cellulosic Mixotrophy (CeMix) (Final Technical Report)
- Arizona State Univ., Mesa, AZ (United States)
- Colorado State Univ., Fort Collins, CO (United States)
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- New Mexico State Univ., Las Cruces, NM (United States)
This novel project, branded CeMIX for cellulosic mixotrophy, targets solutions for several technological barriers limiting the deployment of algae cultivation in sunny, arid regions (specifically the southwest United States). Opening up the region for algae cultivation could increase DOE’s resource assessments and biofuel potential for the U.S. Mixotrophic metabolism in support of liquid fuel production is completely dependent on the availability of waste organic carbon in order to avoid diversion of food resources for fuel production. The use of cellulosic sugar hydrolysate (CSH) produced via the NREL process provided a standardized carbon source for study of the underlying biochemistry and metabolic adjustments to mixotrophy. Mixotrophic metabolism uses both photosynthetic CO2 fixation and sugar oxidation to improve biomass productivity and harvest yield. The project was high-risk, high-reward in the sense that adding organic carbon to algal cultivation is an invitation for rapid-growth, heterotrophic contaminants to overtake the culture and consume mineral nutrients needed for algal growth. To help evade this outcome the project focused on acidophilic red algae that require low pH conditions with 40-48°C optimal temperature profiles that define them as low-range thermophiles. This is the only project in the BETO portfolio to utilize extreme conditions of low pH and high operating temperatures to control pathogens and competitors in mass culture. The project yielded five major outcomes. 1) Harvest densities of 5-10 g ash-free dry weight are easily achieved, providing a 10-fold reduction in water required and dewatering demand. 2) Catabolic repression of photosynthesis in G. sulphuraria is conditionally repressed by low oxygen. 3) Mixotrophic growth on cellulosic hydrolysate consumes all C6 and C5 sugars concomitant with increases in floridean starch with little change in lipid content. Protein content can be manipulated between 35 and 54 wt% by varying the C:N molar ratio from 10:1 to 20:1, respectively. 4) Mixotrophic cultures with up to 50 mM total sugar are remarkably stable at pH 2.5 and daily average reactor temperatures of 40°C. 5) Capital costs for glass tubular photobioreactors are prohibitive for liquid fuel production using a hydrothermal liquefaction processing pathway. The economic outlook for covered raceway ponds is better with a project minimum fuel selling price at $3.32 dm3GE-1.
- Research Organization:
- Arizona State Univ., Mesa, AZ (United States); Colorado State Univ., Fort Collins, CO (United States); National Renewable Energy Lab. (NREL), Golden, CO (United States); New Mexico State Univ., Las Cruces, NM (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Transportation Office. Bioenergy Technologies Office
- DOE Contract Number:
- EE0007562
- OSTI ID:
- 1798517
- Report Number(s):
- DOE-ASU-07562
- Country of Publication:
- United States
- Language:
- English
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