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.

No abstract

System (CIMIS). While the modified Penman-Monteith approach estimates evaporation from an open water body directly, parameter conversions are required to convert pan evaporation and CIMIS landsurface evaporation into open-water-body evaporation. We examined the net effect on financial performance using the System Advisor Model (SAM) and a sensitivity analysis that included estimates of three different solar PV structures at eight different sites along the California network of canals (Fig. 1). In our main results we considered CdTe semiconductor technology but also considered multicrystalline silicon in the sensitivity analysis. The three solar PV structures included a ground-mounted system (Fig. 2a), a steel-truss canal-spanning design that has been deployed in Gujarat, India 26 (Fig. 2b), and a suspension-cable canal-spanning design 27 that has been deployed in Punjab, India 28 (Fig. 2c). Our financial performance analysis includes NPV and levelized cost of energy (LCOE) comparisons of over-canal to ground-mounted designs. Our design comparisons considered enhanced PV performance due to evaporative cooling, and avoided costs for water and aquatic weed mitigation (Fig. 2d and 2e). ResultsHere, we present the results of our water savings, financial performance, and diesel engine retirement analysis. Water savingsEvaporation rates extracted to the locations of the canals and averaged annually are 1716, 1497, and 1570 mm y -1 for the modified Penman, pan evaporation, and CIMIS approaches, respectively. As expected, these estimates of evaporation from canal water surfaces are higher than estimates of evaporation from land surfaces due to the availability of water and surface energy balance. Our surface water evaporation estimates are 11% to 59% higher than California statewide potential evaporation from land surfaces 29,30 . Similarly, previous estimates of evaporation from water surfaces on lakes are generally larger than potential evaporation from land surfaces 31 .

Sustainability is a common goal and catchphrase used in conjunction with seafood, but the metrics used to determine the level of sustainability are poorly defined. Although the conservation statuses of target or nontarget fish stocks associated with fisheries have been scrutinized, the relative climate impacts of different fisheries are often overlooked. Although an increasing body of research seeks to understand and mitigate the climate forcing associated with different fisheries, little effort has sought to integrate these disparate disciplines to examine the synergies and trade-offs between conservation efforts and efforts to reduce climate impacts. We quantified the climate forcing per unit of fish protein associated with several different U.S. tuna fishing fleets, among the most important capture fisheries by both volume and value. We found that skipjack tuna caught by purse seine, a gear type that is often associated with relatively high bycatch of nontarget species, results in lower climate forcing than all other sources of proteins examined with the exception of plants. Conversely, skipjack tuna caught by trolling, a gear type that is often associated with relatively low bycatch of nontarget species, generates higher climate forcing than most other protein sources with the exception of beef. Because there is a range of selectivity and climate forcing impacts associated with fishing gears, examining the trade-offs associated with bycatch and climate forcing provides an opportunity for broadening the discourse about the sustainability of seafood. A central goal of more sustainable seafood practices is to minimize environmental impacts, thus mitigation efforts—whether they target conservation, habitat preservation, or climate impacts—should consider the unintended consequences on fisheries conservation.

Fishing vessels were recently found to be the largest source of black carbon ship emissions in the Arctic, suggesting that the fishing sector should be a focus for future studies. Here we developed a global and Arctic emissions inventory for fishing vessel emissions of short‐lived and long‐lived climate forcers based on data from a wide range of vessel sizes, fuel sulfur contents, engine types, and operational characteristics. We found that previous work generally underestimated emissions of short‐lived climate forcers due to a failure to account for small fishing vessels as well as variability in emission factors. In particular, global black carbon emissions were underestimated by an order of magnitude. Furthermore, our order of magnitude estimate of the net climate effect from these fishing vessel emissions suggests that short‐lived climate forcing may be particularly important in regions where fuel has a low sulfur content. These results have implications for proposed maritime policies and provide a foundation for future climate simulations to forecast climate change impacts in the Arctic.

Fish oil is primarily extracted from small marine pelagic fishes, reducing their availability for marine wildlife forage and artisanal fishing catches that support food security in lower income coastal nations. A primary use of fish oil is in feeds for aquaculture, the world’s fastest growing food sector. Efforts to transition fed aquaculture to sustainability includes replacing fish oil in aquafeeds with more environmentally responsible alternative ingredients. The heterotrophic marine microalga Schizochytrium sp., one of the first commercialized alternatives, lacks an open-access, systematic analysis of environmental impacts of substituting fish oil with heterotrophic microalgae from biorefineries. This study compared the “cradle to factory-gate” life cycle impacts of fish oil to whole-cell or extracted oil of Schizochytrium combined with canola oil. We conducted an attributional life cycle assessment using inventory data collected from published literature and patents and received feedback on commercial relevance of model assumptions from industry advisors. We examined sugar from a Brazilian sugarcane biorefinery and sucrose from U.S. sugar beets as feedstocks for heterotrophic cultivation of Schizochytrium; and compared life cycle impacts of extracting Schizochytrium oil using solvent-free microwave extraction to conventional solvent extraction. Results were that: cultivation processes had the largest overall effect for both products in both regions; whole-cell Schizochytrium combined with canola oil had significantly lower environmental impacts, in all assessed categories, than Schizochytrium oil blended with canola oil; and conventional solvent extraction had significantly lower environmental impacts compared to solvent-free microwave extraction except global warming potential. Schizochytrium products, compared to fish oil, had substantially lower biotic resource depletion and, in the case of whole cells combined with canola oil, had significantly lower global warming potential but higher impacts for all other categories, primarily because commercial Schizochytrium production used sugar feedstocks as carbon and energy sources. The mix of lower and higher environmental impacts of Schizochytrium products illustrates the importance of openly identifying environmental trade-offs to inform evidence-based decisions for commercial practices. Environmental impacts should also be weighed against potential human health benefits of maintaining omega-3 fatty acids and avoiding contaminants in fish flesh when considering alternatives to fish oil.