Restoring pre-industrial CO2 levels while achieving Sustainable Development Goals

A framework is presented with examples of technologies capable of achieving carbon neutrality while sequestering suﬃcient CO to ensure global temperature rise less than 1.5 ° C (after a small overshoot), then continuing to reduce CO levels to 300 ppm within a century. Two paths bracket the continuum of opportunities including dry, sustainable, terrestrial biomass (such as , 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 CO sequestration simultaneously increases ocean health and biodiversity. Both paths can accomplish net-zero fossil-CO 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 CO-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 CO/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-CO for about $ 26/tonne, avoided cost.

a. An integrated system design that includes seeding, growing, and harvesting.

155
Cycle processes revealed an opportunity for HTL to produce carbon-negative biofuel. This facilitated creation of a low-bioelectricity, high-biofuel path to global carbon neutrality with substantial 157 sequestration (labeled Pfuel path).

158
Combining information on available wet (for HTL) and dry (for Allam Cycle gasification) waste 159 and purpose-grown biomass and plastic with data on Allam Cycle power generation allowed another 160 high-bioelectricity, low-biofuel path (Pelectric). The estimates calculated over these two paths are 161 presented in Section 3.1, Tables 1 and 2, and discussed throughout this paper.

162
In summary, the method combined theoretical studies from the MARINER program with other

215
These three numbers were provided by three other MARINER teams and shown on tab 6. The 216 four sets of numbers were totaled to a potential of 60 billion dry tonnes/yr (D44) at a projected 217 biomass-weighted average cost of $110/dry tonne (D45).

218
The other important unpublished data are HTL cost projections shown in Tab Tables 1 and 2 show the global energy, biomass, and CDR calculated in this paper. Table 1 (SS   248 tab 2) outlines possible approaches to achieve net-zero emissions while using some fossil fuel by: (1) 249 capturing and storing all CO2 emitted by fossil-fuel electricity generation to make such electricity 250 production carbon neutral, (2) capturing and storing some CO2 from biofueled electricity production 251 to offset some non-captured fossil fuel use, (3) capturing and storing most of the byproduct CO2 252 produced when biomass is converted to biofuel to offset other fossil fuel emissions, and (4) carbon-253 negative biofuels and electricity replacing fossil-fueled transportation. Negative emissions from the 254 captured and stored bio-CO2 offset the use of fossil fuels (mainly natural gas) for heating and 255 industry. After net zero CO2 emissions, increasing biomass-fueled energy production with carbon 256 capture removes CO2 from the atmosphere at the rates indicated in Table 2 Year when 2 trillion tonnes of CO2 are removed from atmosphere and ocean and permanently sequestered Year 2130 2110 * Although the Pfuel path shows only a small increase in per-capita electricity from present levels, it assumes that the UN SDG goal of doubling the global rate of improvement in energy efficiency by 2030 continues so that universal access is achieved, but little additional energy is needed. The Pfuel path is an extreme case in that it assumes little increase in electric vehicles with most powered by carbon neutral biofuels.
Tables 1 and 2 quantify the steps in Figure

289
The darker green and thicker arrows are paths to more bio-CO2 storage (CO2 removed from the 290 environment, i.e., negative emissions). The lighter green and thinner arrows lead to carbon-neutral 291 emissions, including bio-CO2 emissions from combustion by airplanes, or wind and solar power.

292
The costs, values, and relative local scale for each process and arrow in Figure 3 can be modified      317 8) There are many ways to permanently sequester CO2 (subsection 3.7). 318

319
Tables 1 and 2 indicate the necessary scale of total biomass production. A higher proportion of 320 the biomass for the "low bioelectricity, high biofuel" path will be "wet" such as macroalgae, food and 321 green waste. A higher proportion of the biomass for the "high bioelectricity, low biofuel" path will 322 be "dry" such as Miscanthus, paper and plastic.

323
Wet biomass production starts with seafood grown in total-ecosystem aquaculture (TEA) or

340
The Pfuel path presumes increasing ocean net primary productivity by 40% or about 40 billion 341 dry tonnes/yr. The Pelectric path projects increasing terrestrial net primary productivity by 15% or about 342 17 billion dry tonnes/yr. Currently, the world's net primary productivity is near 210 billion tonnes/yr 343 of biomass (Field et al., 1998). Total land productivity is about 110 billion tonnes on an area of 344 150 million km 2 . Ocean productivity is about 96 billion tonnes on 360 million km 2 . This suggests that 345 oceans are under-producing relative to land; this could be remedied by ensuring nutrient recycling 346 and building structures supporting macroalgae or seagrass production in the photic zone. See SD 347 Section 3.3 for a discussion of how macroalgae-for-fuel expansion into "nutrient deserts" can amplify 348 ocean biodiversity more than traditional marine protected areas.

349
Primary conclusions from Table 3 include:

350
• Globally, there is excess potential additional biomass, 60−100 billion dry tonnes/yr, 351 much more than the 30−40 billion dry tonnes/yr needed in these projections. Thus,

352
there is no need to use wood from forests, which is often regarded as unsustainable 353 (Hudiburg et al., 2013). More discussion in SD.

354
• There is more than enough organic solid waste (including mixed biosolids, paper,

357
• Every kind of biomass or waste (wet or dry) can contribute, which means every 358 country can participate in some form of biomass production.
• While there are obvious differences in maximum scale and cost, most biomass 360 sources can be turned into a viable industry.

361
• These numbers are speculative in that macroalgae projections are based on 362 theoretical studies, not physical demonstration projects. Terrestrial material scale and cost are from references in SS tab 4. Macroalgae scale and cost are interpolated from TEAs anticipating technologies and systems (SS tab 6). The analyses were funded by the U.S. DOE's ARPA-E MARINER Program (2017b). 2 Terrestrial material energy-return ratios are from references in SS tab 4. Macroalgae energy-return ratios were defined as the lower heating value of macroalgae for the energy out (Eout) and the energy required for planting, growing, harvesting, and transporting to the energy processor for energy in (Ein). The embedded energy in the structure, ships, etc. is approximated by the capital cost of those items converted to $/dry tonne. The operating energy is approximated as the cost of biofuel or the capital cost of ambient energy (solar, wave, wind) converted to $/dry tonne. 3 Solid waste pays a disposal fee as if the HTL unit was a landfill. Landfill fees in the U.S. range from $30−100/wet ton ($120−400/dry tonne) (Environmental Research & Education Foundation, 2019). Negative values (because solid waste has a disposal fee) could produce oil for $0/barrel. Ein is the difference between the energy expended now to collect and transport solid waste to landfills compared to the energy expended to collect, transport, and process it at HTL facilities. Quantity from Kaza et al.  Figure 11 in SD suggests that wet biomass delivered to the biofuel process (HTL) for less than about $120/dry tonne would produce biocrude oil for less than about $70/barrel. The bottom line is that there is more biomass potentially available at reasonable prices than is 365 needed for either the Pelectric path, which uses 17 billion dry tonnes of dry biomass for Allam Cycle and 13 billion dry tonnes of wet biomass (food/green waste + macroalgae) for HTL, or the Pfuel path, 367 which uses 4 billion dry tonnes of dry biomass and 39 billion dry tonnes of wet biomass (see SS Tabs 368 2, 3, 4).

369
The availability of large quantities of ocean biomass relieves pressure on terrestrial sources of  The 17 billion dry tonnes/yr of terrestrial biomass for the Pelectric path (Table 1)

382
Other nutrients can be recovered from the solid residues.

383
The 39 billion dry tonnes/yr of oceanic biomass for the Pfuel path, requires cycling 1.2 billion 384 tonnes/yr of nitrogen (SS tabs 12 and 18) from the ecosystem-to-energy process and back.

398
• If nutrients after energy production were not recycled, waste-treatment costs using 399 conventional "wastewater" biologic nutrient removal processes would increase the 400 cost of bio-oil by $60/barrel.

401
• 1.2 billion tonnes of inorganic nitrogen is available in 2−3 million km 3 of deep ocean 402 water. Removing the inorganic nitrogen (and other nutrients) from a few million km 3 403 of deep ocean water each year is not sustainable. Temporarily upwelling a smaller 404 amount of deep ocean water to start and expand primary production may be 405 acceptable.

406
• Upwelling deep ocean water for nutrient supply brings up CO2, drops surface water 407 pH (ocean acidification), and might increase the amount of CO2 in the air (Chan et al.,

409
• Several processes (in addition to HTL, such as anaerobic digestion (Laurens et al.

425
There are many processes that convert wet biomass or wet organic waste to energy. There are 426 many processes that convert most plastics (a dry material) to the raw material for new plastics or 427 energy. HTL is the only process that converts both as a blended feedstock into energy. Eventually, all 428 the plastic will be made from plants or biocrude and become biocrude or new plastics in a circular 429 economy.

430
Because it produces biocrude, oil companies view an HTL facility as if it were a large oil well.

431
All the existing oil handling and consumption infrastructure mean the transition from fossil fuel to 432 biofuel is as fast as the waste collection, macroalgae production, and HTL facilities can scale. Even 433 so, many factors, which vary with location, will determine which of the variety of processes is best 434 for that location.

467
Allam Cycle power plants can produce electricity and byproduct liquid CO2 using any biofuel 468 or fossil fuel. Initially, we propose they run on fossil fuels (natural gas or gasified coal) but be 469 converted to biofuels as rapidly as biofuels become available. Because the fossil-fuel supply chain 470 and much of the electrical distribution system is already in place, fossil-fueled Allam Cycle carbon-471 neutral power plants can replace all expansions and replacements for fossil-fuel electricity production 472 in less than two decades.

473
There are more designs for electricity with carbon capture and storage than just Allam Cycle.

518
SD includes more discussion of the concepts and results in

522
Legacy CO2 is commonly thought of as CO2 from emissions already in the atmosphere and ocean

534
That is concentrating the CO2 about 2,500 times from a little over 0.04% in air to >95%. Allam Cycle 535 power plants always capture the combustion CO2 when they produce electricity, so the added cost 536 for capture is zero.

549
• CO2 capture from HTL -HTL produces bio-crude plus fuel gas that could be 550 combusted with air such that it produces gas with a high fraction of CO2 (10 to 20%)  Table 5.

556
• Hybrid of HTL co-located with Allam Cycle -HTL's byproduct fuel gas and CO2 at 557 1 bar would be blended and provided as fuel (low-grade fuel gas) to the Allam Cycle.

567
The fourth added cost is sequestration of the pure, compressed CO2.   Table 4 shows negative costs (a credit) for those able to 573 sell CO2 for EOR (see more discussion in SD).

604
• The hybrid of HTL co-located with Allam Cycle has about the same added cost for 605 sequestering CO2 as does Allam Cycle alone (greatly reducing the sequestration cost 606 for the byproduct fuel gas and CO2 generated during HTL).

607
• HTL biocrude and biogas made from purpose-grown biomass are likely to cost much 608 more than coal or natural gas as shown in the bottom two rows of Table 5. Therefore, 609 we assume essentially no HTL biocrude-from-macroalgae will be fed into Allam

610
Cycle plants for electricity production; it will be used for transportation fuels.

611
SS tab 16 includes a traditional calculation of "avoided" or "breakeven emissions penalty" costs.

614
Allam Cycle power plant burning $11/GJ HTL biocrude instead of fossil oil for the same $11/GJ, no gas sales

$26
Hybrid co-located HTL and fossil-fired (some HTL biogas) Allam Cycle capturing and compressing CO2 from both processes. Same $/GJ for biomass or fossil fuel, no gas sales

$26
Standalone HTL facility using by-product biogas internally with internal capture and compression of by-product CO2, no gas sales

$75
Using historic capture and compression average cost of $65/tonne plus the same $10/tonne for sequestration. Allam Cycle power plant burning $11/GJ HTL biocrude in place of $7.6/GJ LNG (approximate), no gas sales

$90
Higher fuel cost increasing electricity price is most of the added expense. Allam Cycle power plant burning $11/GJ HTL biocrude in place of $2.5/GJ coal (approximate), no gas sales $180 Table 1 shows globally about 28 billion tonnes/yr of fossil-and bio-CO2 being sequestered on 620 either path at net zero emissions. With mostly co-located HTL and Allam Cycle facilities, the global 621 cost is 28 billion tonnes/yr times $26/tonne, which rounds to $730 billion/yr.

622
A range of 28 to 38 billion tonnes/yr of bio-CO2 is being sequestered in Table 1 on either path for 623 reducing atmospheric CO2 concentrations (carbon dioxide removal (CDR)). Suppose an additional 20 624 billion tonnes/yr of fossil-CO2 is generated and sequestered. The average net mass sequestered 625 between the two paths is 53 billion tonnes times $26/tonne (from Table 5), which rounds to $1,400 626 billion/yr with mostly co-located HTL and Allam Cycle facilities.

627
If HTL is not co-located with Allam Cycle facilities, both paths would use $75/tonne for HTL

691
Install multi-fuel energy systems that produce sequestration-ready CO2. The "multi-" includes 692 coal, natural gas, and biomass. Include ways to recycle nutrients from the energy process to grow 693 more food and biomass-for-energy. Developing countries might earn income from developed 694 countries by growing terrestrial biomass to fuel the developing country's electricity production and 695 sequestering the bio-CO2 less expensively than can be done in developed countries. Co-locate the         to about 0.3% of the world's oceans (see SS tabs 6 and 18). By growing more food in less ocean, marine 737 protected areas could be increased. Production of high-protein food in the ocean could facilitate 738 transition of grain-for-meat production to grain-for-people production as well as increased energy 739 crops, forests, and wildlife habitat with lower GHG emissions. Structures supporting seafood-740 production reefs are similar to those used for macroalgae-for-biofuel production. Seafood production 741 and macroalgae-for-biofuel equipment could be co-developed on a single structure.

742
All countries can benefit from safe handling of biohazard wastes and mixed-solid wastes in 743 general with low, even negative, disposal fees using HTL to produce 20 million barrels/day (3 million 744 tonnes/day) of biocrude oil from wastes by 2050. Additional benefits include less plastic trash 745 reaching the ocean, less methane emissions from landfills, and profitably clearing beached Sargassum.

746
Allam Cycle power plants reduce the avoided cost (i.e., the economic penalty as defined by 747 Rubin et al. 2015) to capture, compress, transport, and sequester one tonne of CO2 from the >$60/tonne 748 (in 2020) for other power plant CCS technologies to less than $0/tonne for early adopters (Table 5,

756
When co-located, the HTL and Allam Cycle facilities synergistically produce carbon-negative 757 biofuel. Both technologies can be co-located with other businesses and waste-handling facilities to 758 maximize this closed-loop economy that demonstrates improved energy efficiencies (e.g.,

759
pasteurizing human and medical wastes with "waste" heat and manufacturing high-performance 760 plastics from biocrude oil that when recycled more easily convert to biocrude or electricity).

761
Each country or community can consider which sustainable-development components and 762 associated technologies best fit their resources and goals. Every sustainable development listed in 763 Section 3.9 can start now and grow while achieving SDGs with high economic efficiency. These

780
• Total-ecosystem aquaculture must be designed for continued biodiversity and seafood 781 production even with some fish species moving toward the poles as the tropical oceans