In recent years, microalgal feedstocks have gained immense potential for sustainable biofuel production. Thermochemical, biochemical conversions and transesterification processes are employed for biofuel production. Especially, the transesterification process of lipid molecules to fatty acid alkyl esters (FAAE) is being widely employed for biodiesel production. In the case of the extractive transesterification process, biodiesel is produced from the extracted microalgal oil. Whereas In-situ (reactive) transesterification allows the direct conversion of microalgae to biodiesel avoiding the sequential steps, which subsequently reduces the production cost. Though microalgae have the highest potential to be an alternate renewable feedstock, the minimization of biofuel production cost is still a challenge. The biorefinery approaches that rely on simple cascade processes involving cost-effective technologies are the need of an hour for sustainable bioenergy production using microalgae. At the same time, combining the biorefineries for both (i) high value-low volume (food and health supplements) and (ii) low value- high volume (waste remediation, bioenergy) from microalgae involves regulatory and technical problems. Waste-remediation and algal biorefinery were extensively reviewed in many previous reports. On the other hand, this review focuses on the cascade processes for efficient utilization of microalgae for integrated bioenergy production through the transesterification. Microalgal biomass remnants after the transesterification process, comprising carbohydrates as a major component (process flow A) or the carbohydrate fraction after bio-separation of pretreated microalgae (process flow B) can be utilized for bioethanol production. Therefore, this review concentrates on the cascade flow of integrated bioprocessing methods for biodiesel and bioethanol production through the transesterification and biochemical routes. The review also sheds light on the recent combinatorial approaches of transesterification of microalgae. The applicability of spent microalgal biomass residue for biogas and other applications to bring about zero-waste residue are discussed. Furthermore, techno-economic analysis (TEA), life cycle assessment (LCA) and challenges of microalgal biorefineries are discussed.
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Asia is the leading aquaculture region in the world, contributing to 85% of total world aquaculture production. Of the top 10 aquaculture producing countries 9 are Asian with China accounting for more than 65% of Asian production. Aquaculture in Asia contribute more than 80% of an estimated 17-20 million aquaculture farmers in Asia providing livelihoods, food security and export earning power but at the same time there are growing problems with environmental impact from large numbers of small-scale producers and the difficulties in planning and management of further development. Traditional integrated aquaculture systems which are sustainable environmentally continue to play an important role for many small-scale farmers and local communities, particularly at the subsistence level. However, recently more productive and profitable aquaculture practices have developed using formulated pelleted feed and allowing intensification of production. Small-scale producers are characterised small farm units and low productivity but in many cases, aquaculture develops in clusters of small-scale farms favouring sheltered bays, estuarine areas and coastal fringe, lakes and dams. Whilst individually such farms create little environmental impact, the cumulative effects of large numbers of farms in “clusters” can be significant. Mitigation of these environmental impacts is difficult due to the number of individual small scale-farmers. However the effects of cumulative environmental impact can be reduced by the introduction of carrying capacity estimation using models before development, the implementation of Better Management Practices and control of feed quality and feeding strategy and management can reduce the cumulative impact.
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The objective of this report is to review the history, results, and conclusions of research on marine biomass conducted under the sponsorship of the U.S. Navy, gas industry (American Gas Association and Gas Research Institute), and U.S. Department of Energy. The scope of this program was to determine the technical and economic feasibility of production of substitute natural gas (SNG) from marine biomass using anaerobic digestion as a conversion process. This work began in 1968 and continued until about 1990, ending as a result of low energy prices in the U.S. and reduced emphasis in renewable energy.
The focus of this report is on growth of seaweeds and conversion to methane via anaerobic digestion. Since this program ended in 1990, interested parties met seve ral times to continue discussing this topic and possibilities for obtaining new support its further development. The results of our dialogue at these meetings are summarized, including alternative ideas for marine energy farms and conversion of methane to methanol. Research from other concurrent programs sponsored by the gas industry to produce SNG from biomass and wastes is summarized and compared with those presented for marine biomass.
These programs addressed herbaceous and woody species, water hyacinth and sludge generated from aquatic plant waste treatment systems, and municipal solid waste. For each of these feedstock categories, feedstock growth or collection (in the case of wastes), harvesting, conversion by anaerobic digestion, and systems and economic analysis are addressed. Also discussed is the potential impact of this form of renewable energy on mitigation of carbon dioxide emissions from fossil fuels. In general, marine biomass was the least developed of these systems by this research effort. The greatest uncertainties were related to the technical and economic feasibilityof large-scale growth of macroalgae in the open ocean, especially concerning provision of nutrients. The anaerobic conversion aspect of this system was better developed and is not likely to be significantly different than that developed for other similar feedstocks.
The gas cost estimates for marine biomass systems were 3-6 times those for U.S. fossil fuel gas. Terrestrial biomass systems were developed to a greater extent by this research because of a better prior knowledge of growth and harvest of the feedstocks emphasized. SNG from this category was about 2-3 times that of U.S fossil fuel gas. The lowest cost was associated with SNG from municipal solid waste, reflecting the tipping fee received for treating this waste. However, these costs are not competitive with landfilling.
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Given their advantages of high photosynthetic efficiency and non-competition with land-based crops, algae, that are carbon-hungry and sunlight-driven microbial factories, are a promising solution to resolve energy crisis, food security, and pollution problems. The ability to recycle nutrient and CO2 fixation from waste sources makes algae a valuable feedstock for biofuels, food and feeds, biochemicals, and biomaterials. Innovative technologies such as the bicarbonate-based integrated carbon capture and algae production system (BICCAPS), integrated algal bioenergy carbon capture and storage (BECCS), as well as ocean macroalgal afforestation (OMA), can be used to realize a low-carbon algal bioeconomy. We review how algae can be applied in the framework of integrated low-carbon circular bioeconomy models, focusing on sustainable biofuels, low-carbon feedstocks, carbon capture, and advances in algal biotechnology.
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The University of New Hampshire, in partnership with local fishing cooperatives and a commercial marine fish hatchery, and with collaboration from several regional research institutions, established an offshore aquaculture research and development facility in the Gulf of Maine in 1999. The offshore platform, located 9.66 km (6 miles) off the New Hampshire coastline in 56.39 m (185 feet) of water, is fully permitted for commercial production. It consists of a submerged
grid mooring system that can accommodate four submersible cages for finfish culture, two submerged longlines for suspended molluscan shellfish culture, and surface structures that include remotely operated feeders, acoustic biotelemetry systems, and oceanographic instrumentation.
The facility serves as the field site for applied research and technology development, evaluation, and technology transfer for the Open Ocean Aquaculture Project funded by the National Oceanic and Atmospheric Administration. The goal of the project is to stimulate the development of an environmentally sustainable offshore aquaculture industry, thereby increasing seafood production, creating new employment opportunities, and contributing to regional and national economic and community development. To date, fish species cultured at the site have included summer flounder (Paralichthyus dentatus), Atlantic halibut (Hippoglossus hippoglossus), haddock (Melanogrammus aeglefinis), and Atlantic cod (Gadus morhua). In addition, blue mussels (Mytilus edulis) and Atlantic sea scallops (Placopecten magellanicus) have been grown on the adjacent submerged longlines. -
A framework is presented with examples of technologies capable of achieving carbon neutrality while sequestering sufficient CO2 to ensure global temperature rise less than 1.5°C (after a small overshoot), then continuing to reduce CO2 levels to 300 ppm within a century. Two paths bracket the continuum of opportunities including dry, sustainable, terrestrial biomass (such as Miscanthus, paper, and plastic) and wet biomass (such as macroalgae, food, and green waste). Suggested paths are adaptable, consistent with concepts of integral ecology, and include holistic, environmentally friendly technologies. Each path addresses food security, marine plastic waste, social justice, and UN Sustainable Development Goals. Moreover, oceanic biomass-to-biofuel production with byproduct CO2 sequestration simultaneously increases ocean health and biodiversity. Both paths can accomplish net-zero fossil-CO2 emissions by 2050. Both paths include: (1) producing a billion tonnes/yr of seafood; (2) collecting six billion dry tonnes of solid waste (any mix of organic waste, paper, and plastic) to produce twenty million barrels/day of biocrude; and (3) installing a million megawatts of CO2-sequestering (Allam Cycle) electric power plants initially running on fossil fuels. Resulting food production, solid waste-to-energy, and fossil-fueled Allam Cycle infrastructure will strengthen the economies in developing countries. Next steps are (4) sequestering four billion tonnes of byproduct CO2/yr from solid waste-to-biofuel by hydrothermal liquefaction; (5) increasing macroalgae-for-biofuel production; (6) replacing fossil fuel with terrestrial biomass for Allam Cycle power plants; (7) recycling nutrients for sustainability; and (8) eventually sequestering a total of 28 to 38 billion tonnes/yr of bio-CO2 for about $26/tonne, avoided cost.
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A framework is presented with examples of technologies capable of achieving carbon neutrality while sequestering sufficient CO2 to ensure global temperature rise less than 1.5°C (after a small overshoot), then continuing to reduce CO2 levels to 300 ppm within a century. Two paths bracket the continuum of opportunities including dry, sustainable, terrestrial biomass (such as Miscanthus, paper, and plastic) and wet biomass (such as macroalgae, food, and green waste). Suggested paths are adaptable, consistent with concepts of integral ecology, and include holistic, environmentally friendly technologies. Each path addresses food security, marine plastic waste, social justice, and UN Sustainable Development Goals. Moreover, oceanic biomass-to-biofuel production with byproduct CO2 sequestration simultaneously increases ocean health and biodiversity. Both paths can accomplish net-zero fossil-CO2 emissions by 2050. Both paths include: (1) producing a billion tonnes/yr of seafood; (2) collecting six billion dry tonnes of solid waste (any mix of organic waste, paper, and plastic) to produce twenty million barrels/day of biocrude; and (3) installing a million megawatts of CO2-sequestering (Allam Cycle) electric power plants initially running on fossil fuels. Resulting food production, solid waste-to-energy, and fossil-fueled Allam Cycle infrastructure will strengthen the economies in developing countries. Next steps are (4) sequestering four billion tonnes of byproduct CO2/yr from solid waste-to-biofuel by hydrothermal liquefaction; (5) increasing macroalgae-for-biofuel production; (6) replacing fossil fuel with terrestrial biomass for Allam Cycle power plants; (7) recycling nutrients for sustainability; and (8) eventually sequestering a total of 28 to 38 billion tonnes/yr of bio-CO2 for about $26/tonne, avoided cost.
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As aquaculture production expands, we must avoid mistakes made during increasing intensification of agriculture. Understanding environmental impacts and measures to mitigate them is important for designing responsible aquaculture production systems. There are four realistic goals that can make future aquaculture operations more sustainable and productive: (1) improvement of management practices to create more efficient and diverse systems at every production level; (2) emphasis on local decisionmaking, human capacity development, and collective action to generate pro- ductive aquaculture systems that fit into societal constraints and demands; (3) development of risk management efforts for all systems that reduce disease problems, eliminate antibiotic and drug abuse, and prevent exotic organism introduction into local waters; and (4) creation of systems to better identify more sustainably grown aquaculture products in the market and promote them to individual consumers. By 2050, seafood will be predominantly sourced through aquaculture, including not only finfish and invertebrates but also seaweeds.
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Responses of the germination and growth of Ulva prolifera parthenogametes to gradients of temperature and light were evaluated. Results showed that U. prolifera parthenogametes could not germinate at 5 °C and 35 °C, and at all temperatures combined with dark conditions, but had high germination rates at the temperature of 15–25 °C and photosynthetically active radiation (PAR) of 80–160 μmol m–2 s–1. There was a significant interaction between temperature and PAR on the growth rate of U. prolifera germlings germinated from parthenogametes (P < 0.001), which indicated that U. prolifera germlings achieved the highest growth rate at specific combinations of temperature and light. Growth rate of U. prolifera germlings germinated from parthenogametes was as high as 93.5–99.2 % d−1 at combined conditions of 22 °C and 26 °C with 100 μmol m−2·s−1 and 200 μmol m−2·s−1, respectively. Ulva prolifera parthenogametes survived over two months at the temperature of 3 °C, and germinated and grew when the temperature increased from 3 °C to 13 °C. Ulva prolifera thalli germinated from parthenogametes maintained a relatively better state under the condition of 30 °C and 10 μmol m−2·s−1 compared with thalli cultured at 30 °C combined with PAR of 100 μmol m−2·s−1 and 200 μmol m−2·s−1, respectively. These results suggest that U. prolifera parthenogametes may largely contribute to green tides due to their high germination and growth rates, and their ability to survive over stressful environments in the southern Yellow Sea.
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Macroalgal blooms of Ulva lactuca and Hypnea musciformis have been problematic in shallow coastal waters around agricultural and urbanized regions of Maui, Hawai‘i for decades. Observations have highlighted the correspondence between these blooms and elevated nutrient levels from the adjacent land-use, however little evidence exists regarding the effects of nutrient enrichment on the blooming and non-blooming macroalgae in the area. To determine if elevated nutrient levels influence H. musciformis physiology, we conducted a nutrient enrichment (+N, +P, and +N+P) experiment and measured growth, photosynthetic status, and pigment absorbance. Phycobilin pigments were significantly reduced in the no addition and +P treatment and maintained in those with N additions, suggesting that H. musciformis can use phycobilins to store N. We conducted a second, larger experiment with additions of secondarily-treated wastewater effluent on the bloom forming species Acanthophora spicifera, H. musciformis, and U. lactuca and the common non-bloom forming species, Dictyota acutiloba. All samples were initially depleted of potential N stores and measured for growth, photosynthetic status, and N uptake rates; H. musciformis and U. lactuca were also assessed for micro nutrient uptake, % tissue N, and d15N values. Growth rates of D. acutiloba, H. musciformis, and U. lactuca increased with increasing % wastewater effluent addition and concentrations of TN and NO3 and those of the bloom forming species were 2-fold higher. All species increased photosynthetic capacity and saturation irradiance with increasing % wastewater effluent addition and concentrations of TN and NO3 . U. lactuca was the most sensitive to low N conditions, evidenced by declines in light capturing efficiency. All species utilized a substantial amount of N over 24 h. H. musciformis and U. lactuca also (1) utilized micro nutrients: iron, manganese, molybdenum, and zinc, (2) decreased % tissue N in low N conditions, (3) increased % tissue N in response to elevated N conditions, and (4) expressed elevated d15N values with increasing additions of wastewater effluent. These results demonstrate that in Hawai‘i, the bloom forming species H. musciformis and U. lactuca, have similar physiological responses to decreased and increased nutrient levels.
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Marine Agronomy Group, CAFNRM, UH-Hilo
200 W. Kawili st., HI 96720, USA
Contact: Marine.Agronomy.Group@gmail.com
Funding for this web portal is provided by the World Wildlife Fund and the University of Hawaii-Hilo.