Algae are an attractive biofuel feedstock because of their fast growth rates and improved land use efficiency when compared with terrestrial crops. Process train components needed to produce algal biofuels include (1) cultivation, (2) harvesting, and (3) conversion into usable fuel. This paper compares various process train options and identifies knowledge gaps presently restricting the production of algal biodiesel and algae-derived biogas. This analysis identified energyintensive processing and the inability to cultivate large quantities of lipid-rich algal biomass as major obstacles inhibiting algal biodiesel production. Anaerobic digestion of algal biomass requires fewer process train components and occurs regardless of lipid content. In either scenario, the use of wastewater effluent as a cultivation medium seems necessary to reduce greenhouse gas emissions and maximize water use efficiency. Furthermore, anaerobically digesting algal biomass generated from lowtechnology wastewater treatment processes represents an appropriate technology approach to algal biofuels that is poorly investigated. Coupling these processes can improve global health by improving sanitation, while providing a cleaner burning biogas alternative to indoor biomass cooking systems typical of less-developed areas. Water Environ. Res., 83, 326 (2011).

Aquafeed manufacturers have reduced, but not fully eliminated, fishmeal and fish oil and are seeking cost competitive replacements. We combined two commercially available microalgae, to produce a high-performing fish-free feed for Nile tilapia (Oreochromis niloticus)—the world’s second largest group of farmed fish. We substituted protein-rich defatted biomass of Nannochloropsis oculata (leftover after oil extraction for nutraceuticals) for fishmeal and whole cells of docosahexaenoic acid (DHA)-rich Schizochytrium sp. as substitute for fish oil. We found significantly better (p < 0.05) growth, weight gain, specific growth rate, and best (but not significantly different) feed conversion ratio using the fish-free feed compared with the reference diet. Fish-free feed also yielded higher (p < 0.05) fillet lipid, DHA, and protein content (but not significantly different). Furthermore, fish-free feed had the highest degree of in-vitro protein hydrolysis and protein digestibility. The median economic conversion ratio of the fish-free feed ($0.95/kg tilapia) was less than the reference diet ($1.03/kg tilapia), though the median feed cost ($0.68/kg feed) was slightly greater than that of the reference feed ($0.64/kg feed) (p < 0.05). Our work is a step toward eliminating reliance on fishmeal and fish oil with evidence of a cost-competitive microalgae-based tilapia feed that improves growth metrics and the nutritional quality of farmed fish.

OMEGA is a system for cultivating microalgae using wastewater contained in floating photobioreactors (PBRs) deployed in marine environments and thereby eliminating competition with agriculture for water, fertilizer, and land. The offshore placement in protected bays near coastal cities co-locates OMEGA with wastewater outfalls and sources of CO 2-rich flue gas on shore. To evaluate the feasibility of OMEGA, microalgae were grown on secondary-treated wastewater supplemented with simulated flue gas (8.5% CO 2 V/V) in a 110-liter prototype system tested using a seawater tank. The flow-through system consisted of tubular PBRs made of transparent linear low-density polyethylene, a gas exchange and harvesting column (GEHC), two pumps, and an instrumentation and control (I&C) system. The PBRs contained regularly spaced swirl vanes to create helical flow and mixing for the circulating culture. About 5% of the culture volume was continuously diverted through the GEHC to manage dissolved oxygen concentrations, provide supplemental CO 2 , harvest microalgae from a settling chamber, and add fresh wastewater to replenish nutrients. The I&C system controlled CO 2 injection and recorded dissolved oxygen levels, totalized CO 2 flow, temperature, circulation rates, photosynthetic active radiation (PAR), and the photosynthetic efficiency as determined by fast repetition rate fluorometry. In two experimental trials, totaling 23 days in April and May 2012, microalgae productivity averaged 14.1 ± 1.3 grams of dry biomass per square meter of PBR surface area per day (n = 16), supplemental CO 2 was converted to biomass with >50% efficiency, and >90% of the ammonia-nitrogen was recovered from secondary effluent. If OMEGA can be optimized for energy efficiency and scaled up economically, it has the potential to contribute significantly to biofuels production and wastewater treatment.

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