Unless humanity achieves United Nations Sustainable Development Goals (SDGs) by 2030 and restores the relatively stable climate of pre-industrial CO2 levels (as early as 2140), species extinctions, starvation, drought/floods, and violence will exacerbate mass migrations. This paper presents conceptual designs and techno-economic analyses to calculate sustainable limits for growing high-protein seafood and macroalgae-for-biofuel. We review the availability of wet solid waste and outline the mass balance of carbon and plant nutrients passing through a hydrothermal liquefaction process. The paper reviews the availability of dry solid waste and dry biomass for bioenergy with CO2 capture and storage (BECCS) while generating Allam Cycle electricity. Sufficient wet-waste biomass supports quickly building hydrothermal liquefaction facilities. Macroalgae-for-biofuel technology can be developed and straightforwardly implemented on SDG-achieving high protein seafood infrastructure. The analyses indicate a potential for (1) 0.5 billion tonnes/yr of seafood; (2) 20 million barrels/day of biofuel from solid waste; (3) more biocrude oil from macroalgae than current fossil oil; and (4) sequestration of 28 to 38 billion tonnes/yr of bio-CO2. Carbon dioxide removal (CDR) costs are between 25–33% of those for BECCS with pre-2019 technology or the projected cost of air-capture CDR.

This paper describes the “SeaweedPaddock” system to profitably grow and harvest open-ocean Sargassum sp. as a sustainable source of macroalgal biomass and biofuel. The US Department of Energy Advanced Research Projects Agency - Energy (ARPA-E) initiated the MacroAlgae Research Inspiring Novel Energy Research (MARINER) program to develop technologies to eventually sustainably harvest macroalgae at 80 per dry metric ton (DMT). The University of Southern Mississippi team is characterizing an unmoored SeaweedPaddock; analyses include tow speed and energy required to avoid hazards, farm design to minimize biomass loss, economical harvesting, and nutrient supply. Initial results indicate that nighttime “smart towing” could allow the SeaweedPaddock system to produce macroalgae at full scale at costs below the ARPA-E goal provided that Sargassum grows at sufficient rates during the day after having been confined all night in a moving fence and that sufficient nutrients are made available. Cost projections for a successful, intensive, scaled system could be competitive with current prices for fossil fuels.

The US Department of Energy Advanced Research Projects Agency - Energy (ARPA-E) MacroAlgae Research Inspiring Novel Energy Research (MARINER) program is encouraging technologies for the sustainable harvest of large funding research of macroalgae for biofuels at less than $80 per dry metric ton (DMT). The Ocean Forests team, led by the University of Southern Mississippi, is developing a complete managed ecosystem where nutrients are transformed and recycled. The team's designs address major bottlenecks in profitability of offshore aquaculture systems including economical moored structures that can withstand storms, efficient planting, managing and harvesting systems, and sustainable nutrient supply. The work is inspired by Lapointe [1] who reported yields of Gracilaria tikvahiae equivalent to 127 DMT per hectare per year (compared with standard aquaculture systems in the range of 20 to 40 DMT/ha/yr). This approach offers the potential for breakthrough yields for many macroalgae species. Moreover, mini-ecosystems in offshore waters create communities of macroalgae, shellfish, and penned finfish, supplemented by visiting free-range fish that can increase productivity, produce quality products, and create jobs and income for aquafarmers. Additional benefits include reduced disease in fish pens, cleaning contaminated coastal waters, and maximizing nutrient recycling. Cost projections for a successful, intensive, scaled system are competitive with current prices for fossil fuels.

Oceans, islands, and coastal a as threatened by humanity’s rapi atmospheric greenhouse gas concentr remaining 30% of Earth’s surface. Y discussion for sequestering the dominant CO2, involves deep sub-earth geologic stru relatively small areas in continental pla needs a secure carbon storage alternative in more countries. Secure Seafloor Co (SSCS) is an alternative that could safely tons of CO2. The paper presents a geophysical, chemical, and economic mode research shows that appropriate undisturb will prevent contact with seawater for mi osmosis loss per millennium). CO2 hyd meters is a rock-like solid denser than wate assessment predicts a mass ratio of store needed of 1,700:1. The projected cost to gaseous CO2 to a liquid, convert the liq inside a geosynthetic membrane, monitor a structures is approximately $16 per ton of

Oceans, islands, and coastal areas are at least as threatened by humanity's rapidly increasing atmospheric greenhouse gas concentrations as the remaining 30% of Earth's surface. Yet most of the discussion for sequestering the dominant greenhouse gas, CO2, involves deep sub-earth geologic structures limited to relatively small areas in continental plates. Humanity needs a secure carbon storage alternative that is available in more countries. Secure Seafloor Container Storage (SSCS) is an alternative that could safely store trillions of tons of CO2.The paper presents a computational geophysical, chemical, and economic model of SSCS. Our research shows that appropriate undisturbed geosynthetics will prevent contact with seawater for millennia (<;0.06% osmosis loss per millennium). CO2 hydrate below 500 meters is a rock-like solid denser than water. Our life cycle assessment predicts a mass ratio of stored-CO2: materials needed of 1,700:1. The projected cost to compress pure gaseous CO2 to a liquid, convert the liquid to hydrate inside a geosynthetic membrane, monitor and maintain the structures is approximately $16 per ton of CO2.

Ocean Afforestation, more precisely Ocean Macroalgal Afforestation (OMA), has the potential to reduce atmospheric carbon dioxide concentrations through expanding natural populations of macroalgae, which absorb carbon dioxide, then are harvested to produce biomethane and biocarbon dioxide via anaerobic digestion. The plant nutrients remaining after digestion are recycled to expand the algal forest and increase fish populations. A mass balance has been calculated from known data and applied to produce a life cycle assessment and economic analysis. This analysis shows the potential of Ocean Afforestation to produce 12 billion tons per year of biomethane while storing 19 billion tons of CO2 per year directly from biogas production, plus up to 34 billion tons per year from carbon capture of the biomethane combustion exhaust. These rates are based on macro-algae forests covering 9% of the world's ocean surface, which could produce sufficient biomethane to replace all of today's needs in fossil fuel energy, while removing 53 billion tons of CO2 per year from the atmosphere, restoring pre-industrial levels. This amount of biomass could also increase sustainable fish production to potentially provide 200 kg/yr/person for 10 billion people. Additional benefits are reduction in ocean acidification and increased ocean primary productivity and biodiversity. (C) 2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.