Negative emission technologies

C H A P T E R

1 Negative emission technologies Francisca M. Santos, Ana L. Gonc¸alves and Jose´ C.M. Pires LEPABE

Laboratory for Process Engineering, Environment, Biotechnology and Energy, Faculty of Engineering, University of Porto, Porto, Portugal

1.1 Introduction Carbon dioxide (CO2), an important greenhouse gas (GHG), has been added to the atmosphere by anthropogenic activities, mainly by the burning of fossil fuels. As a consequence, severe changes in the world’s climate are happening, and different ecosystems are being threatened [1]. Since the pre Industrial era, the population and economic growth have largely increased the global average atmospheric CO2 concentration. Between 1750 and 2018 the CO2 levels have risen from 280 parts per million (ppm) to, approximately, 408 ppm [2,3]. Global CO2 emissions are about 36 Gt CO2/year [4], where 91% are originated from the combustion of fossil fuels [5]. As a consequence, the ocean has absorbed about 20% 40% of the CO2 emitted to the atmosphere since the Industrial Revolution [6]. This increase has a greater impact on the chemistry of the ocean surface, especially on the levels of hydrogen ion concentrations (H1). The continuous rise in the atmospheric CO2 increases the levels of H1 in the ocean, which leads to its acidification. Surface ocean pH is already 0.1 U lower. At this rate the decrease of ocean pH is expected to be 0.4 U by the end of the century and 0.8 U by 2300 [7,8]. Simultaneously, the carbonate equilibrium is affected, resulting in dramatic impacts on marine life. Reducing ocean pH decreases the amount of carbonate ions available, and it may become more difficult for some species, such as coral reefs and calcareous plankton, to form biogenic calcium carbonate [9]. Thus these species are more vulnerable to dissolution, and their habitats are severely threatened. It is estimated that already 30% was damaged, and approximately 60% may be lost by 2030 [10]. In addition, as a GHG, CO2 can absorb and emit infrared radiation, which affects the global temperature. The planet’s average temperature has risen about 0.9 C since 1880 [11], mainly driven by the increase of CO2 emissions, causing the melt of glaciers and other ice and, consequently, increasing sea levels [12]. In order to reduce the atmospheric CO2 concentration, several nations recognize the urgent need to commit to a low-carbon economy [13,14]. In 2015 countries adopted an

Bioenergy with Carbon Capture and Storage DOI: https://doi.org/10.1016/B978-0-12-816229-3.00001-6

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international agreement to combat climate change under the United Nations Framework Convention on Climate Change (21st Conference of the Parties—COP21). The Paris Agreement aims to avoid the increase in global average temperatures in 2  C and to make efforts to limit this increase to 1.5  C above preindustrial levels. In order to limit warming the total amount of CO2 emitted needs to be finite, and it includes the utilization of both preventive and remediation strategies [15]. Preventive measures are related with (1) improving energy efficiency, (2) increasing the use of low-carbon fuels, (3) promoting the use of renewable energy sources, and (4) using geoengineering approaches [for example, afforestation and reforestation (AR), which increase the natural carbon sink]. Remediation methods are linked to carbon capture and storage (CCS) techniques [16,17]. The anthropogenic sources of CO2 can be divided into two categories: large stationary sources (such as power plants and industrial activities) and dispersed sources (mainly from transportation). While CCS can reduce CO2 emissions from large sources (around 85% 90%), the aim of reducing anthropogenic CO2 emissions close to zero requires CO2 capture from diffuse emissions as well (e.g., cars, trucks, airplanes) [18,19]. Since the capture from diffuse sources may be technically impossible, due to its large number, CO2 can be captured from the atmosphere using negative emission technologies (NETs), which offset these emissions. Capturing CO2 from the atmosphere may be more expensive than capturing from stationary points, but this supplementary approach presents some advantages: (1) CO2 capture is sector independent, in other words, it can capture CO2 emissions from both diffuse and point sources; (2) transportation infrastructures may be avoided since the CO2 capture unit can be placed anywhere; (3) the separation process is less affected by the presence of other pollutants (e.g., nitrogen oxides, sulfur oxides) since their atmospheric concentration is much lower when compared to flue gases [17,18,20]. Nevertheless, the NETs’ feasibility to meet the required scenarios is still questioned. Technical and social barriers, such as the absence of political actions, public understanding and acceptability of these technologies, or the side effects that NETs could have, are conditioning the scale-up of the technology [21,22]. NETs encompass several techniques, and it can be divided into two routes: (1) direct air capture through physicochemical processes [absorption, adsorption, ocean alkalinity enhancement (OAE), and soil mineralization] and (2) indirect air capture through biological processes [afforestation, ocean fertilization, algal culture, bioenergy with CCS (BECCS), and biochar]. This chapter aims to present an overview of the main NETs, also presenting the advantages and drawbacks of each technology.

1.2 Direct air capture The concept of capturing CO2 from air is not new. It was previously applied as a lifesupport system in submarines and spacecraft, but it was mentioned for the first time for climate change mitigation purposes in 1999 by Lackner et al. [23]. Since half of the CO2 emissions come from diffuse sources, its capture from the atmosphere is essential to comply with the targets of limiting the warming within 1.5  C 2  C. However, this technology presents challenges regarding the high energy demands associated to the low CO2 concentration on ambient air (approximately 350 times lower than a typical coal-based flue gas [17]). Large air volumes need to pass through the absorbers to collect significant amounts

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of CO2. Therefore capture technologies that use heat, cool, or pressurized air cannot be applied in air capture due to their economical unfeasibility [23,24]. The atmospheric CO2 can be captured from the following methodologies: (1) absorption, (2) adsorption, (3) OAE, and (4) soil mineralization.

1.2.1 Absorption Absorption is a process where the gas (ambient air) captured enters in contact with a physical or chemical solvent in an absorption column. The solvent has specific characteristics that only absorb CO2 and let the other gases pass [25]. The CO2-rich solution is usually transferred to a regeneration column, where the CO2 is removed, and the solvent is recycled to be further reused. Physical absorption is based on Henry’s law, and the dissolution of CO2 on solvents is attributed to electrostatic interactions and the van der Waals forces. The absorption process occurs under high pressures and low temperatures, whereas the reverse favors the desorption process. Typical absorbents are Selexol (dimethyl ether or polyethylene glycol) and Rectisol (methanol). In general, these absorbents are less corrosive in the presence of other gases, less toxic and present low regeneration temperatures [26,27]. However, the regeneration of CO2 also requires high partial pressure, and significant amounts of energy are needed for pressurization. Therefore physical absorption is not economical for gas streams with low partial pressures [27]. Chemical absorption is currently the most matured technology used for capturing CO2 from flue gases. The chemical solvents are essentially amines, and the most widely used is monoethanolamine (MEA) [28]. The operation occurs at low CO2 partial pressure and low temperatures, and it can capture 75% 90% of the CO2, producing a pure-CO2 stream (99%) [29]. However, this technology presents several challenges regarding (1) the high corrosion rate, (2) the high energy and temperatures requirements for regeneration, (3) the amine degradation (leading to sorbent losses), and (4) the low CO2 capture capacity [g CO2/(g sorbent)] [25]. It is also possible to capture CO2 from ambient air using a wet scrubbing system. The atmospheric CO2 is absorbed into a solution of sodium hydroxide (NaOH), forming a solution of sodium carbonate (Na2CO3). Then, CO2 is recovered by calcination, pressurized, and stored [30,31]. Stolaroff et al. [32] evaluated the capture of CO2 from air using NaOH spray based contactor, estimating the cost and energy requirements. The obtained absorption rate was 3.7 mmol/L/pass, which is equivalent to 0.4 t CO2/year/m2 of contactor cross section. This process has a significant water loss (20 mol H2O per mol of CO2 at 15 C and 65% relative humidity), which can impose a constraint on its deployment. The total energy requirements can range from 190 to 390 kJ/mol in the tested conditions, and the base full-scale system cost is 96 $=tCO2 and can vary between 53 and 127 $=tCO2 , depending on the initial operation parameters. Ionic liquids (ILs) have emerged as a possible alternative to the chemical and physical absorbents. ILs are composed exclusively by ions, which remain liquid at room temperature. Their favorable solvent properties (e.g., high thermal stability, insignificant volatility, tuneable capacity, and high CO2 solubility) make them feasible candidates for absorption process [33]. Due to the thermal stability, ILs can absorb CO2 presenting lower regeneration energy requirements. One constraint of IL is the increase of viscosity with the

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absorption of CO2, which can create some issues regarding solvent pumping and mass transfer kinetics [34]. Another limitation of IL is the high costs compared to organic solvents. So, for an industrial scale, it is necessary to improve their recovery, product isolation and reuse efficiency as well as evaluate the environmental impacts [35]. Ma et al. [36] evaluated the energy consumption of CO2 absorption using IL and a conventional MEA process. The IL selected was the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) ([bmim][Tf2N]). The feed composition was 12.5% CO2, 5% H2O, and 78% N2. The results showed that the IL performed better than the MEA. IL consumed more electricity than MEA, but the thermal energy was substantially lower, which led to global savings on energy consumption of 30.0%. The total cost was also lower for IL (29.9%). The energy consumption for CO2 storage was analyzed, where MEA based had a better performance. For the entire CO2 capture and storage the IL-based process was more economical than MEA-based process.

1.2.2 Adsorption In the adsorption process, air is fed to a bed of a solid adsorbent, which fixes CO2 selectively until the equilibrium is reached. Desorption or regeneration is an important feature for an industrial application of the adsorption process. To reduce the CO2 recovery cost, adsorbents must be regenerable, allowing their reuse for a large number of cycles [18]. CO2 desorption is usually performed by swinging the pressure (PSA) or temperature (TSA). In PSA the adsorption process occurs at high pressures and the swing for low pressures (generally atmospheric pressure) for the desorption process. In TSA, CO2 is desorbed from the solid absorbent by raising the system temperature using hot air or steam injection [19]. PSA has a simpler operation, low power consumption, and fast regeneration. However, the presence of water may lower the CO2 recovery. TSA has longer regeneration times than PSA but presents higher CO2 purity and recovery, avoiding the energy requirements to pressurize CO2. Although CO2 capture by adsorption is only commercialized for high concentrations, for atmospheric CO2 capture, this process has several advantages over the absorption process, such as (1) the low regeneration energy requirements, (2) the smaller environmental concern of the solid waste compared with the liquid waste, (3) resistance to corrosion, and (4) the broader range of operational temperatures [37]. The selection of the adsorbents should take into account the specific surface area, the selectivity, and the regeneration ability. Typical adsorbents are zeolites and activated carbon [19]. However, the atmospheric pressure and the water content in the air affect the adsorption capacities, making these adsorbents not appropriated for air capture [18]. Amine-functionalized solids have higher selectivity at low concentrations, stability, and tolerance to moisture, due to the chemical character of the sorbent adsorbate interaction [25]. In fact, humid environments can improve the adsorption efficiency. Amine-functionalized adsorbents have some disadvantages: (1) at high temperatures, the amine adsorbents degrade; and (2) TSA is required for desorption (due to the chemical bonding), which can reduce the adsorption capacity [38]. Wurzbacher et al. [39] evaluated the adsorption/desorption process to capture CO2 from air using an amine-functionalized sorbent. Desorption process was performed using a

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combined temperature-vacuum swing to avoid the compression requirements during adsorption and the adsorbent degradation during desorption. The sorbent CO2 capture capacity was determined under different operational conditions (10 150 mbar, 74 90 C, and 0% 80% relative humidity). A desorption capacity of 0.30 mmol/g (at 10 mbar and 90 C) was achieved, producing a stream with a CO2 purity of 95.8%. In addition, the adsorption process was enhanced under humid conditions.

1.2.3 Ocean alkalinity enhancement The ocean covers approximately 70% of the earth’ surface and contains around 50 times more carbon compared to the atmosphere. However, the increase of atmospheric CO2 concentrations has been rising ocean acidity [40]. The OAE is gaining attention for its carbon sequestration potential, and it can simultaneously counteract ocean acidification. Its main idea is accelerating the natural CO2 neutralization process by the application of minerals [e.g., Mg2SiO4, Ca(HCO3)2, Ca(OH)2], which bind to CO2 and form bicarbonate in aqueous form. Thus the CO2 produced by several sources (industrial and diffuse) is sequestered from the atmosphere, increasing the total amount that is stored in the ocean [41]. The natural weathering consumes around 0.25 Gt C/year (1 Gt C 5 109 t C) of atmospheric CO2, and OAE can increase to 0.53 0.61 Gt C/year [42,43]. The main advantage of this NET is that CO2 is converted into inoffensive, stable, and environmental-friendly carbonate mineral, which permanently fixes CO2. On the other hand the slow reaction, the management of the carbonate by-product and the process cost, and environmental impacts (mineral extraction processing and transportation) are some concerns regarding the implementation of this technology as a viable solution to carbon sequestration [44]. Moreover, the consequences of adding large volumes of mineral particles on the marine life are still unknown, requiring exhaustive studies before its implementation [45,46]. Renforth and Kruger [47] presented a techno-economic assessment of ocean liming with magnesium carbonate minerals. For each ton of sequestered CO2, 1.9 t of Mg2SiO4 is needed. The electric energy and thermal requirements were approximately 4.9 and 2.2 GJ/t CO2, respectively.

1.2.4 Soil mineralization The carbon pool present in the soil is about 2500 Gt, which is 3.3 times higher than the carbon present in the atmosphere (760 Gt) [48]. Atmospheric CO2 can be sequestered into the soils in three ways: (1) accumulation of organic carbon, (2) rock weathering (promoting the dissolution of inorganic carbon), and (3) precipitation of carbonate materials. Ko¨hler et al. [49] investigated the use of olivine for carbon sequestration in the Amazon and Congo basins. The dissolution of 1.8 and 0.4 Gt of olivine in the land of Amazon and Congo has sequestered 0.5 and 0.1 Gt C/year, respectively. However, for these dissolution and sequestration rates, there is a higher rate of leaching of alkalinity to the rivers, which increases the pH value to 8.2. Besides the increase of water pH, the erosion of silicate rocks into rivers and coral reefs might increase turbidity and sedimentation, and their impacts on biodiversity are unknown [50]. In addition, the amount of rock mass is huge, and the emissions associated

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with mining, comminuting, transport, and application can affect the net CO2 sequestration efficiency of enhanced weathering [51]. On the other hand, soil-enhanced weathering has the potential of decreasing soil acidification and heavy metal toxicity and enhancing the nutrient supply in nutrient-poor soils, promoting higher crop yields. It is estimated that if carbon sequestration in degraded soils occurs, an additional 0.4 1.2 Gt C/year could be removed [52]. Agricultural practices that increase soil carbon sequestration should also be considered and assessed as a mitigation policy, while benefitting from increased crop production [53].

1.3 Indirect air capture In the natural carbon cycle, nature captures CO2 from the atmosphere and converts into organic carbon (carbohydrates, cellulose, and lipids) through photosynthesis, while simultaneously produces oxygen [18]. The main advantage of the biological route over the direct capture methods is the lower energy requirements. Biological processes use solar energy for CO2 sequestration, while the industrial processes require heat or electrical energy [54]. In addition, the direct air capture methodologies are expensive, and the long-term efficacy has not yet been proven [55]. The indirect air capture can be divided into five processes: (1) AR, (2) ocean fertilization, (3) algal culture, (4) BECCS, and (5) biochar. The description of each process is represented in the next sections, and the estimates of the combined NET potential are presented in Table 1.1.

1.3.1 Afforestation and reforestation Afforestation is the conversion of abandoned and degraded agricultural lands into forests, while reforestation is the replantation of trees in deforested land. Both practices can contribute to negative emissions since the growth of additional plant sequesters atmospheric CO2 and naturally sink it in their biomass and in the soil. Ni et al. [56] estimated that an average of 2 2.5 Gt C/year could be stored in world forest, with a higher contribution of tropical forests. Humpeno¨der et al. [60] found that the large-scale afforestation could TABLE 1.1 Combined negative emission technology (NET) potential of the indirect air capture methodologies. Methodology

NET potential (Gt C/year)

Reference

Afforestation and reforestation

2 2.5

Ni et al. [56]

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0.68 2.7

Haszeldine and Scott [57]

Ocean fertilization

0.34

Lenton [42]

Algae culture

0.26

Chung et al. [58]

Biochar

0.27 0.49

Woolf et al. [59]

All

3.55 6.29

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provide an accumulative removal of more than 189 Gt C by 2095. Large afforestation programs have been undertaken, and in 2010 the afforested area accounted for more than 264 Mha (1 Mha 5 106 ha). In China the existing afforestation projects increased the forest area in 2 Mha/year in the 1990s, increasing to 3 Mha/year since 2000. This resulted in an estimated total emission reduction of 4.4 Mt CO2 eq. [61,62]. However, soil organic carbon stock is affected by several practices such as deforestation and changes on global land use, and it is estimated to cause the release of 20% 50% of the soil carbon to the atmosphere. Kindermann et al. [63] estimated that if deforestation would be reduced by 50%, a total emission of 1.5 2.7 Gt CO2/year could be reduced in the period from 2005 to 2030. On the downside, large-scale afforestation might increase the food prices due to the higher competition for land between forest and agriculture. In addition, the location of the afforested areas plays an important role in the effectiveness of this mitigation measure. Afforestation decreases the surface albedo and raises the amount of radiation that is absorbed, which increases the temperature of the surface and the lower boundary layer [64,65]. Boreal forest has a cooling effect due to the high albedo, and its reduction can have a negative contribution to climate change. Betts [66] used a climate model to simulate where the benefits of afforestation (i.e., carbon sequestration) outweighed the biophysical effects (i.e., decreased surface albedo). In boreal areas the negative biophysical effects outweighed the biogeochemical effects, and this contributes to global warming. However, afforestation has several benefits regarding the climate change in lower latitudes.

1.3.2 Bioenergy with carbon capture and storage BECCS is the combination of two mitigation options: biomass combustion for energy generation and CCS [67]. This combination is considered one of the most feasible solutions for CO2 mitigation. Biomass is widely used to generate electricity and heat and can be transformed into biofuel for other applications (e.g., transportation). The feedstock can vary from forest residues to agricultural wastes to sewage sludge [68]. The CCS are technologies developed to capture CO2 from industrial sources, transporting, injecting and storing into deep geological reservoirs. The combination of these two technologies can result in a net zero or negative CO2 emissions. The energy generation from biomass is already considered a neutral carbon process because CO2 is absorbed from the atmosphere and converted to biomass, which is again released upon their combustion. By having an installed CCS the capture of these emissions has the potential to transform this process into a negative net emission energy production [69]. It is estimated that BECCS can contribute to an emission reduction of 0.68 2.7 Gt C/year [57]. BECCS presents some challenges regarding the effectiveness of its application. First, BECCS requires a large area of land, and similarly to AR, this adds significant pressure on food prices. Since the rotation of the feedstock used for bioenergy is shorter, the water and nutrients requirements are higher compared with other NET. In 2100 it is estimated that the water consumption from BECCS would correspond to 1.5% of total yearly freshwater withdrawals [45]. The nutrients used for biomass growth are depleted from the fields, when the biomass is harvested, which augments the need for fertilizers. Thus this nutrient depletion increases GHG emissions and energy consumption [70]. Moreover, the GHG

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emissions associated with the harvesting and processing cast doubt on the feasibility of BECCS to result in a negative removal of CO2 from the atmosphere [67]. Another concern is that CCS is still not commercially established and to scale up BECCS as a NET, the resolution of the technical and social issues of CCS, as well as understanding the environmental impacts, is required [71].

1.3.3 Ocean fertilization Marine phytoplankton has a crucial role in the global carbon cycle. Their photosynthesis consumes not only CO2 but also macronutrients (e.g., nitrogen—N—and phosphorus—P) and micronutrients (e.g., iron—Fe). Ocean fertilization proposes the addition of nutrients to the ocean surface, which ultimately controls the amount of carbon that is sequestered. Since the levels of N and P are usually greater than Fe levels, the addition of Fe into the ocean can stimulate the photosynthesis and enhance carbon sequestration [40]. Without the nutrient limitation, photosynthetic organisms remove large quantities of CO2 in the surface ocean, which creates an air sea flux. While one part is consumed by other organisms in the food chain, the other sinks into the deep sea, which takes the sequestration carbon with it [55]. Wolff et al. [72] evaluated the impact of iron fertilization in oceans with high-nutrient and low-chlorophyll waters and found that the addition of iron increases primary production, stimulating phytoplankton growth. The other nutrients (N and P) can also enhance carbon sequestration and is already occurring in the ocean. The leakage of P from human activities (sewage, detergent, and mining) to coastal regions contributes to the sequestration of 0.18 Gt C/year, and it is estimated to sink 0.34 Gt C/year in the open oceans [42]. However, there are some uncertainties regarding ocean fertilization [73]. First, the excess of nutrients can lead to eutrophication, which can reduce oxygen levels (anoxia), change phytoplankton species (development of undesired algal blooms), and lower biological diversity. Second, fertilization may decrease in a small extension the pH in deeper zones. Third, ocean fertilization can affect global nutrient distribution, where some areas can experience a reduction on nutrient supply, affecting the biological productivity, which ultimately can have effects on economic activities (e.g., fisheries).

1.3.4 Algae (seaweed and microalgae) culture Microalgae are photosynthetic microorganisms found in marine and freshwater environments. Its photosynthetic efficiency is 10 times higher than terrestrial plants, achieving higher growth rates and biomass productivities, with some species doubling their biomass within a few hours. Microalgae can assimilate CO2 from different sources: (1) from the atmosphere [74], (2) from flue gases [75], and (3) from carbonates dissolved in the culture medium. However, the low concentration present in the atmosphere or the toxic compounds (such as sulfur dioxide or nitrogen oxides), which can be present in flue gases might inhibit microalgal growth. Traditionally, microalgae can be cultivated in open ponds (e.g., raceway ponds) or closed photobioreactors. Open systems have an economic advantage over the closed systems because they have a simpler construction and operation; however, they have a higher

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dependency on external factors, which can reduce biomass productivities [76]. Microalgae have several applications, including wastewater treatment, biofuels, food and feed production, and cosmetics [77]. Despite the numerous applications, the economic viability of microalgal cultures can be achieved by the integration of different processes (e.g., CO2 capture, wastewater treatment, energy production, biorefinery approach) and improvement of photobioreactors’ efficiency. Seaweeds (or macroalgae) have high photosynthetic efficiency, high CO2 capture rates, and the growth rates far exceed those of terrestrial biomass [78]. On average, seaweeds are composed of 30% carbon, which represents a sequestration of 0.26 Gt C/year into their biomass [58]. A Korean study has demonstrated that a cultivated seaweed farm can sink 2.7 t C/ha/year [79]. Open-ocean seaweed culture has environmental and economic advantages over terrestrial plans, namely, the lower requirements for land use, freshwater, and fertilizers. Besides the CO2 sequestration potential, the harvested seaweeds can be used to produce bioenergy, while producing high added-value by-products [78]. For instance a cultivation area of 9% of the ocean surface could provide bioenergy to replace the energy from fossil fuels, while removing 53 Gt CO2/year from the atmosphere [80].

1.3.5 Biochar Biochar is a carbon-enriched biomaterial generated in the combustion of biomass through a process called pyrolysis [71]. In pyrolysis, biomass (e.g., crop and forestry residues, manure, municipal and industrial wastes) is decomposed at temperatures higher than 400 C, in the complete or near absence of oxygen. As a result, syngas, bio oil, and biochar are produced [59,81]. As it has a high-carbon content (approximately 60% 90%) [71], the application of biochar into soils is considered a significant and long-term approach to sink atmospheric CO2 in terrestrial ecosystems. Besides the benefits of reducing emissions and sequestering of GHG, biochar presents several positive effects on the quality of the soil [82]. Adding biochar to soils increases crop production due to the improvement of soils’ physicochemical and biological properties, such as increased water retention, soil pH, and microbial activity [83]. Moreover, biochar can help to reduce agricultural emissions from fertilizers usage due to the lower fertilizer requirements [71]. Woolf et al. [59] estimated the capacity of biochar for mitigating climate change. The authors predicted under three different scenarios that biochar production could avoid the emissions of 1.0 1.8 Gt CO2/year. Although biochar has the combined potential of reducing GHG emissions and increasing crop yields, long-term impacts on soil, fauna, and flora and ecological risks are unknown, and future research is needed [84].

1.4 Conclusion Regardless of its low atmospheric concentration, capturing CO2 from the air might be feasible and essential to fulfilling the established mitigation goals. This chapter presents the main NETs and their current advances. The integration of different technologies can reduce global process costs. However, NETs should be seen as a complementary action to

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achieve the CO2 reduction required. In addition, the scale that NETs were modeled should be tested in different scenarios, and its potential environmental impacts should be completely understood before the application of any technology.

Acknowledgments We would like to acknowledge the projects POCI-01-0145-FEDER-031736 PIV4Algae—Process Intensification for microalgal production and Valorization and POCI-01-0145-FEDER-006939 (Laboratory for Process Engineering, Environment, Biotechnology and Energy—UID/EQU/00511/2013), financed by the European Regional Development Fund (ERDF), through COMPETE2020—Programa Operacional Competitividade e Internacionalizac¸a˜o (POCI) and by FCT/MCTES through national funds (PIDDAC), as well as by project “LEPABE-2-ECO-INNOVATION”— NORTE-01-0145-FEDER-000005, funded by Norte Portugal Regional Operational Programme (NORTE 2020), under PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). J.C.M. Pires acknowledges the FCT Investigator 2015 Programme (IF/01341/2015). A.L. Gonc¸alves acknowledges the FEUPLEPABE-PIV4Algae-IC.

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