To harvest or not? Tradeoffs between SOC maintenance and overall environmental performance of harvesting crop residues for the bioeconomy

doi:10.21203/rs.3.rs-3093300/v1

Download PDF

Research Article

To harvest or not? Tradeoffs between SOC maintenance and overall environmental performance of harvesting crop residues for the bioeconomy

https://doi.org/10.21203/rs.3.rs-3093300/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

The transition to zero-net emissions raises trade-offs between the services competing for sustainable carbon sources. Here, we performed a consequential LCA to understand the full environmental performance of managing 1 tonne of wet crop residue to produce sustainable marine fuels, while preserving or enhancing the SOC stocks in French croplands. Three management scenarios were considered: i) decay of crop residues on soils (reference), ii) conversion of crop residues to hydrotreated pyrolysis oil (HPO) to replace heavy fuel oil in maritime transportation, with biochar return to soil, and iii) conversion of crop residues to cryogenic liquefied bio methane (bio-LNG) to replace liquefied natural gas in cargo ships, with digestate return to soil. Besides the replacement of the fossil fuels, a system boundaries expansion was applied to account for the valorisation of the coproducts obtained along the whole supply chain of each system. Results per tonne of crop residues show, for all impacts assessed, a better environmental performance of using crop residues for maritime biofuels in comparison to their direct ploughing to soils, for all environmental impacts assessed. Notably, major GHG savings are observed, representing avoided emissions of 563 and 946 kgCO_2etww^− 1 of crop residues for the HPO and bio-LNG, respectively. The impact was scaled to the national potential that can be harvested for each pathway without losing SOC stocks (C-neutral harvest), implying a greater potential for the HPO pathway. While bio-LNG was the most performant pathway per tonne of residues (with the exception of marine eutrophication and particulate matter), the scaled results show greater savings with the HPO pathway, except for freshwater eutrophication and water scarcity. The results show that converting crop residues to biofuels while returning the recalcitrant coproduct of the conversion pathway to soils allows, in the HPO case, net environmental benefits for all the assessed environmental impacts as well as for SOC stocks. While bio-LNG shows net savings in most impacts, it shows a net impact for marine eutrophication because of the nitrogen losses associated with the digestate management. Overall, the results do not show, for the assessed pathways and impacts, a trade-off between SOC maintenance and net environmental impacts, if a C-neutral harvest is ensured with the co-product return to soil. This reflects the importance of fossil fuels substitution beyond the sole climate impact.

Ecological Modeling

Renewable Resources

Environmental Chemistry

Geochemistry

LCA

maritime biofuels

cryogenic liquified biomethane

climate change

Bioeconomy, in particular bioenergy, plays a key role in achieving the 2050-climate-neutrality goal pledged by national [1–3] and supranational [4–6] entities. However, the transition to low fossil carbon economies raises trade-offs between the involved sectors striving for renewable carbon. One current issue is that posed by the soil carbon lock-up and crop residue harvesting [7–9] competition. Soil organic carbon (SOC) is crucial for soil health because it regulates the biogeochemical cycles involved in soil fertility [10], crop productivity [11], and climate change mitigation through carbon sequestration [12]. However, the SOC dynamics and evolution are regulated by the equilibria between C inputs from plants and exogenous organic matter (EOM) (e.g., animal manure, organic fertilizers) [13, 14] and the outputs related to heterotrophic respiration [15]. Therefore, recommendations suggest limiting the harvesting of crop residues to generic values depending on the crop type [7, 16–18] to avoid SOC disturbances. These constraints hinder the sourcing of green carbon to feed bioeconomy conversion pathways.

Previous studies [19, 20] have investigated the concurrence between SOC enhancement and crop residues removal, with clear positive synergies observed when the final use of crop residues is accounted for and the carbon is partly returned in a transformed stabilized state (e.g., biochar, digestate, hydrochar) [21, 22]. Moreover, the SOC response to changes in C inputs in agricultural lands is spatially explicit, in other words, it depends on the specific site pedology, climate, and farming management practices [14, 23, 24].

Our previous study [20] determined the spatial-explicit amount of crop residues that can be harvested in French croplands to be used in five specific bioeconomy conversion pathways while preserving SOC stocks. There, we demonstrated that the often-suggested removal limit (31.5% of harvestable biomass in France [25]) can be well surpassed without losing SOC if the bioeconomy coproduct is returned to the soil (i.e., pyrolysis and gasification biochar, hydrochar, and digestate) allowing a surplus 71–225 PJ for the bioeconomy. The study was later replicated in a tropical context, for the specific case of Ecuador (Chap. 3), revealing similar conclusions with an estimated C-neutral harvest potential of 113 PJ from crop residues. However, the scope of these studies was constrained to the soil carbon balance and disregarded other aspects associated with crop residue harvesting. In fact, no previous study has simultaneously evaluated the potential of crop residues to supply the bioeconomy while restraining SOC stock diminishment and assessing the whole environmental implications along the supply chain of the conversion pathway.

This study thus aims at shedding light on the SOC stocks, crop residues, and bioeconomy supply tradeoffs with a special focus on the overall environmental impact of harvesting crop residues for biofuel production, beyond sole SOC stock preservation. To this end, we performed a life cycle assessment (LCA) for biofuel production through pyrolysis and anaerobic digestion, both retained as end-of-intervals conversion pathways in the study of Andrade Diaz et al. [20][1]. The LCA is applied to the specific case of sustainable maritime fuels (SMF) for cargo ships [26]. Therefore, we compare the conventional management of harvestable crop residues (no harvest) to the use of crop residues to produce upgraded fuels as substitutes for marine conventional fuels. The comparison to other upgrading technologies or valorization alternatives (e.g., CHP, grid injection, etc.) is out of the scope of this study.

The case of maritime fuels was selected as a key sector for biofuel implementation because sea transport represents ca. 80% of international trade, consuming 330 Mt of maritime fuels per year, of which 77% is heavy fuel oil (HFO) [27]. This consumption accounts for 2–3% of global CO₂, 4–9% SOx, and 10–15% of NOx emissions [28], with a forecasted increase of over 30% from 2015 until 2050, only in the European Union (EU) [29]. In order to address the sea-transport-derived emissions, some regulations have been imposed by the International Maritime Organization (IMO) [30] and the sector has been recently included for the first time in the greenhouse gas emission (GHG) reductions commitment of the EU [31]. The IMO aims to reduce by 50% the total GHG maritime transport emissions by 2050 (compared to 2008) while the EU targets an 80% reduction in the same period (compared to 2020 levels), with special attention to vessels over 5000 gross tonnage (e.g., cargo ships) [29,32,33]. Accordingly, since 2020 maritime fuels must comply with the low sulfur fuel regulation [34,35], which sets the maximum sulfur content of maritime biofuels at 0.5%.

Cargo vessels are predominantly fueled with HFO, which is a low-quality end-of-the-barrel residue from petrol refinement. However, the use of liquefied natural gas (LNG) and marine distillate oil (MDO) for sea transportation has increased to comply with sulfur regulations [28]. In this context, the transition to SMFs is of foremost importance. Therefore, inhere we studied the production of stabilized pyrolysis oil, suitable to substitute HFO and the displacement fossil liquefied natural gas (LNG) by liquefied biomethane, also known as bio-LNG, produced by anaerobic digestion.

2.1 Life cycle assessment implementation

A consequential modeling approach was implemented according to the ISO 14040844 LCA standards [36,37] to track the environmental impacts of SMF. Accordingly, a system boundaries expansion approach was followed to assess displacement multifunctionality and the consequences of using crop residues for SMF production. The main goal of the LCA was to unravel the tradeoffs between the C-neutral harvest of crop residues to supply the bioeconomy and the overall environmental impacts related to the use for which the crop residues are streamed. The consequential methodology [38] considers the counterfactual use of the resources (i.e., the otherwise use of crop residues) and the avoided or induced effects of supplying the resources to the conversion pathways (e.g., coproducts valorization, heat requirements meet through other sources). The functional unit (FU) was defined as “the management of one wet tonne of harvestable crop residues per year”. The FU is common for all the scenarios as the same crop residue composition is considered across the cases to allow comparing the environmental implications of the different management options. The harvestable portion considers the technical constraints described in Andrade Diaz et al. [20].

The geographical scope of the study was set to France, which defined the type of crop residues, energy mix, and legal implications of the scenarios. However, most of the inputs required in the conversion processes were considered to be internationally traded. Therefore, data were selected prioritizing the French scope, and when international markets were required, the “Global”, “Rest of the World” or “Europe” scope were selected. The temporal scope was set to reflect future optimal performance, in particular, the heat requirements were considered to be electrically supplied as defined in the long-term scenarios proposed by Su-ungkavatin [39].

To the extent possible, only marginal suppliers (described in SI1) reacting to a change in demand were considered. Foreground life cycle inventories (LCI), i.e., specific to this study, were built on previous similar works by Brassard et al. [40], Su-ungkavatin [39], and Javourez [41] and were expanded based on published literature and stoichiometry balances as further detailed in the supplementary information (SI) 1. Background LCI data were retrieved from the Eocinvent 3.9.1 consequential database [42]. The LCI data for each scenario, detailing all the input and output flows involved in each operation is detailed in SI2 and SI3 [43]. The environmental impacts of these flows were calculated using the Environmental Footprint (EF) v3.1 Life Cycle Impact Assessment (LCIA) methodology [44] with the open-access software Brightway 2.0 through the Activity Browser interface [45]. Five environmental impacts are addressed (key substances contributing to the impact in brackets): Climate change with a 100-year horizon (CC; CO₂, CH₄, N₂O), particulate matter (PM; soot, NOx, SO₂), eutrophication from exceeding phosphorus (freshwater) and nitrogen (marine) emissions in water reservoirs, and water scarcity (WS). These impacts were selected because they are considered the main drivers for decision-making on the climate urgency context [6] and because the included substances constitute tailpipe emissions in the maritime sector [33]. For the climate change impact in particular, the biogenic CO₂ emissions were considered following a so-called 0/0 approach [46] (uptake and releases having a characterization factor of 0 kg CO₂e per kg CO₂, while induced sequestration flows have a characterization factor of -1 kg CO₂e per kg CO₂ sequestered). This approach considers that biogenic CO₂ emissions are part of a short cycle where exchanges between the different reservoirs over short periods (from few months to several decades) are stable. Conversely, fossil CO₂ emissions are associated with long cycles requiring millions of years to reach equilibrium.

2.2 Case scenarios description

The LCA scenarios reflect the conversion of crop residues to SMFs for cargo vessels. Cargo vessels are predominantly fueled by HFO and propelled using two—stroke engines [47]. However, the IMO [33] reports a 7% decrease in HFO consumption triggered by a 6% and 0.9% increase in marine diesel oil and liquefied natural gas (LNG) over the period 2012–2018. To comply with the market trends, the SMFs scenarios consider i) the substitution of HFO by drop-in pyrolysis bio-oil, and ii) the use of liquefied biomethane (bio-LNG) from anaerobic digestion as an alternative for fossil-LNG. In accordance with the aim of this study, the reference scenario comprises a situation where crop residues are managed by ploughing them back into arable fields to avoid diminishing SOC stocks [24]. The pyrolysis and anaerobic digestion conversion pathways were selected because i) they can produce oil and gas fuels ready to replace the current market fuels, and ii) they represent the extremes of the pathways addressed in our previous studies (Chaps. 3 and 4) evaluating the C-neutral potential of crop residues to supply the bioeconomy.

Both scenarios assess the harvesting of crop residues to source the conversion pathways to produce the selected SMF and return a C-rich coproduct suitable to be spread on soils as a source of Carbon. The observations for 1 wet tonne of crop residue, are then scaled to the national potential rates determined by Andrade et al. [20], to contrast the overall environmental implications of supplying crop residues to the bioeconomy while maintaining the SOC stocks in French croplands.

The crop residues composition, reference scenario y combustion emissions of the fossil fuels are detailed in the SI1.

2.2.1 Pyrolysis scenario: Hydrotreated pyrolysis oil (HPO)

As the main goal of the case study is to supply SMF for cargo shipping, a fast pyrolysis process was selected to favor the bio-crude yields [48]. Along with the bio-crude secondary coproducts in solid (biochar) and gaseous (syngas) states are produced. Pyrolysis biocrude has high water (∼15–30%) and oxygen (20–50%) contents, high acidity (pH 2.5–3), low heating values (15–18 MJ kg^− 1) [49], and may contain traces of ashes, solids, alkali, among others [48] which detriment its potential as a drop-in fuel [27]. Therefore, the biocrude must undergo an upgrading process in order to remove oxygen and increase the H:C ratio to fit fuel standards. Upgrading alternatives for pyrolysis bio-oil include solvent addition, fractionation, catalytic and no-catalytic hydrodeoxygenation (HDO), hot condensation, and catalytic hydrocracking, among others [48,50]. Among these, catalytic HDO coupled with hydrocracking distillation can produce a high-quality bio-oil with suitable quality to completely replace fossil oils [51,52]. However, since ship propulsion systems already operate low-quality fuels, such as HFO, the highly refined pyrolysis oil is more attractive for the aviation than maritime sector. Therefore, here we consider an upgrading process performed by a two-column HDO to produce stable bio-oil, instead of a refined biofuel. The hydrotreated pyrolysis oil (HPO) is then of suitable quality to completely replace HFO in slow-speed engines [32]. The process flow diagram for the HPO, including all the unit operations, counterfactual utilization, and displaced products is shown in Fig. 1 and the details are further explored in SI1.

Briefly, the scenario considers four stages, namely i) biomass supply and pretreatment, ii) fast pyrolysis, iii) HDO upgrading, and iv) HPO combustion onboard. The system boundaries expansion, further explained in section 2.3, includes what is affected by harvesting the crop residues for HPO and the use of the coproducts.

The biomass supply stage accounts for the crop residues harvesting and transportation while the pretreatment considers the storage, size reduction, and moisture conditioning. The harvested crop residues are considered to be baled and stored until their use, with a 4.8% mass loss during storing [53]. The pretreatment includes size reduction to 1–3 mm by means of grinding (1% mass loss as dust), which favors the heat transfer during pyrolysis [40] and drying to achieve a maximum of 10% water content as required by the reactor. The fast pyrolysis process was modeled according to the study by Brassard et al. [40] and the biocrude, aqueous phase (hereon vinegar), biochar and syngas yields reflected the results obtained at a semi-pilot scale auger reactor for the pyrolysis of wheat straw [54] as a proxy of the crop residues in France (the crop residue composition is detailed in SI1). The pyrolysis products are considered to be separated by a condensation system operating with a glycol-water mixture (50:50). The pyrolysis bio-crude is upgraded to reduce the oxygen content to be suitable for substituting HFO to fuel cargo vessels. The coproducts are recovered and used within the system boundaries (Fig. 1).

The upgrading process consists on a catalytic HDO in multiple fixed bed reactors to attain a bio-oil with less than 2% content oxygen. The HDO upgrading was modelled according to the PNL report by Jones [55], and assumptions from Elliot [56] and Vienescu [49] were also considered. The process comprises three stages: i) stabilization, ii) first hydrotreatment, and ii) second hydrotreatment. The three stages require H₂ and catalysts supply. The stabilization and first HDO stage employ a Ruthenium catalyst, while the second HDO is performed using a Molybdenum based catalyst. The overall H₂ consumption of the upgrading stage is of 5.8% H₂ per biocrude feed. The H₂ is assumed to be produced by alkaline water electrolysis according to the model by Javourez [41]. The H₂ plant assumes the partial recovery of excess heat but due to lack of current technology the O₂ is considered to be vented (this is not represented in Fig. 1). The pyrolysis, HDO, and H₂ plant details are compiled in SI1.

The upgraded bio-oil is assumed to be combusted onboard the cargo ship, with emissions assumed according to the Fourth IMO GHG study for MDO.

2.2.2 Anaerobic Digestion (AD) scenario: Cryogenic liquefied biomethane (bio-LNG)

Biogas produced during AD can be directly burned or upgraded to be used as transportation biofuel or injected in the electricity grid. LNG has been one alternative to replace HFO in order to comply with the low sulphur regulations, thus cargo vessels are already transitioning to use this type of fuel [57]. Biogas can be upgraded to biomethane by CO₂ removal, and then compressed to be used as bio-LNG to substitute the fossil-based LNG. Among the myriad of technologies to upgrade biogas to biomethane, cryogenic upgrading is an attractive alternative because it allows to recover CO₂ and compress the CH₄ to be used directly as LNG [58,59]. For this scenario, we considered the cryogenic upgrading of biomethane, by successive steps of compression and freezing (Cryopure technology) to be used in cargo vessels running on steam turbines [28]. This procedure, allows obtaining, besides bio-LNG, pure CO₂, which can be used for other technologies.

The anaerobic digestion (AD) scenario was built on the module developed by Javourez [41] and expanded to include the biogas upgrading as liquefied natural gas (bio-LNG). The AD process considers an infinitely stirred mesophilic bioreactor and includes the following stages: i) pre-treatment, ii) methanation, iii) digestate storage, iv) digestate spreading, and v) biogas valorization. The pretreatment includes the collection of straw as bales, comminution, and extrusion, with an average 3% mass loss [60]. The diffuse feedstock is transported to the collection platform (40 km assumed) and then to the AD facility (40 km assumed), accounting for 80 km of transportation (assumed based on the gasification module of [41]). The pretreated residues are assumed to be ensiled before entering the AD process, with a 1.95% mass loss. The biomethane yield was estimated to be 75% of the theoretical biomethane potential (TBMP), based on Tonini et al. [61] while the TBMP was calculated based on the Symon and Busswell [62], equation using the biochemical composition of the input feedstock.

The heat and electricity requirements were assumed to be represented by 8% auto consumption. The biogas valorization as bio-LNG considers the cryogenic separation of CH₄ based on the sublimation condensation of CO₂ at different temperatures [59]. The bio-LNG is considered to have a CO₂ content below 50 ppm to avoid freezing problems in the process [58]. The cryogenic bio-LNG was assumed to substitute liquefied natural gas (LNG) for marine transportation.

The life cycle inventories (LCI) per technology are based on previously published works and adapted to include the upgrading to produce drop-in fuels suitable for maritime transport in carrier ships. Pyrolysis LCA (biocrude) was based on Brassard et al. [40,54], whereas the bio-LNG scenario is built on the AD module developed by Javourez [41] and expanded to include the cryogenic upgrading according to the Cryopure process [58,63,64]. The bio-LNG was modeled to be fuel a bulk carrier to substitute fossil LNG. The detailed life cycle inventories are presented in the supplementary information SI and repository [43].

2.3 System boundaries

The system boundaries of the scenarios follow a well-to-wake approach [65], including all the processes from the raw materials acquisition to the fuel production and use onboard, accounting for the utilities, waste management, and emissions associated with each life stage of the process. The systems are illustrated in Figs. 1 and 2 and the LCIs are detailed in SI 1, 2, and 3. This study aims to compare the tradeoffs between a C-neutral [20] harvest of crop residues to supply the bioeconomy with the overall environmental implications of the system. Capital goods are included to the extent possible, with a few exceptions because of a lack of data (i.e., ship vessel construction, engine production). Yet, these appear in both what is induced (maritime transportation with biofuel) and avoided (maritime transportation with conventional fuels), and it is considered reasonable to neglect eventual differences in the engines (in terms of the environmental impacts related to their production).

The use of crop residues to produce SMFs avoids counterfactual management. This counterfactual is considered as the reference business-as-usual (BAU) scenario, where the residues decay on soil (i.e., ploughing considered here). Moreover, various coproducts are released along the supply chains in each scenario and are considered to displace marginal services. In the HPO scenario dust, biochar, syngas, and an aqueous stream (vinegar) are produced during the fast pyrolysis stage with an extra syngas release in the upgrading stage (Fig. 1). In the bio-LNG scenario, the coproducts of the whole conversion chain are digestate and CO₂ (Fig. 3). We consider that dust and syngas can be recovered for energy production to displace marginal heat and electricity from the future energy mix of France [39]. Similarly, digestate, vinegar, and biochar are recovered to be spread on fields as soil amendments. Digestate and vinegar are considered to displace mineral fertilizers and inorganic pesticides, respectively, while biochar is used for carbon sequestration (i.e., fertilizing properties of biochar not accounted for). The purified CO₂ stream from the bio-LNG production is accounted to supply the chemical industry, displacing commercial CO₂. It should be noted that the final use of CO₂ is not accounted for, and only the avoided production of CO₂ from fossil sources is considered.

The study examines the environmental impacts of three scenarios and presents the findings for five impact categories. Figure 3 illustrates the key contributors to each impact category for the three scenarios. The bars in the figure represent the positive (above zero) or negative (below zero, avoided processes) environmental impacts, while the triangle indicates the overall net environmental performance of each scenario. The environmental impacts for the other categories assessed within the EFv3.1 methodology are shown in Appendixes SI2 and SI3 for the HPO and bio-LNG scenarios, respectively. The environmental impacts are expressed and analyzed for 1 tonne of wet crop residues (1t_ww).

3.1 Analysis per environmental impact

3.1.1 Climate change

The results for climate change are accounted for on a 0/0 methodology, as explained in section 2.1. Figure 3 shows that both biofuel pathways allows environmental reductions on climate change compared to the BAU. Harvesting and using crop residues for bioeconomy purposes avoids approximately 1519 kgCO_2eq.t_ww⁻¹ that would otherwise be emitted if the residues were simply ploughed into the soils.

The full supply chain for the HPO achieves a net reduction of 562.5 kgC O_2eq.t_ww⁻¹ compared to the BAU. The 20 t.day^− 1 input modeled in the HPO system can therefore reduce 2700 MgCO₂ per year. The major contributor to emissions reduction is the potential C sequestration through biochar spreading, for which 75% of the C is assumed to remain in the soil as SOC after 100 years [66,67]. The biochar recalcitrance can thus induce the sequestration of 463.6 kgCO₂.t_ww⁻¹. Moreover, replacing HFO with HPO, results in a net reduction of ca. 234.33 kg CO₂.t_ww⁻¹, emissions, accounting for the emissions induced by the HPO (3.7 kgCO₂.t_ww⁻¹) and avoided by HFO (-238.0 kg CO_2eq.t_ww⁻¹) production and combustion. The positive emissions are mainly related to the supply and pretreatment stage, attaining 133.3 kgCO_2eq.t_ww⁻¹. The pyrolysis and HDO stages represent emissions of 53.2 kgCO₂, of which 52% corresponds to the pyrolysis process, 8% to the condensation of the pyrolysis products, and 40% to the HDO upgrading of the biocrude. The counterfactual use of coproducts other than biochar (i.e., dust generated during grinding, vinegar and syngas from pyrolysis, and syngas from pyrolysis) represent a total emission of 36.1 kgCO_2eq.t_ww⁻¹. These emissions are offset by the avoided heat, electricity, and pesticide application, which represents 87.2 kgCO_2eq.tww. Therefore, considering the consequences of valorizing the HPO coproducts represents an emissions reduction of 52 kCO_2eq.t_ww⁻¹.

The bio-LNG pathway represents total emission reductions of 945.5 kgCO₂.t_ww⁻¹, of which 84% are attributed to the substitution of fossil LNG (avoided 856.33 kgCO2_e.t_ww⁻¹ production and use) by bio-LNG (emitted 62.7 kgCO_2eq.t_ww⁻¹) combustion to fuel the cargo vessel. While the pretreatment and AD stages release 36.63 kgCO_2eq.t_ww⁻¹, the cryogenic liquefaction avoids the emission of 238.7 kg CO_2eq.t_ww⁻¹. Both the AD and upgrading stages account for the emissions related to methane slips during the process and pipeline injection. Albeit digestate avoids 71.3 kgCO_2eq.t_ww⁻¹ by replacing mineral fertilizers, its management (i.e., storage and spreading) releases 121.6 kgCO_2eq.t_ww⁻¹ with a total net contribution to emissions of 50.2 kgCO_2eq.t_ww⁻¹.

3.1.2 Freshwater eutrophication (EUF)

The SMFs scenarios avoid 8.66 x10^− 3 kgPO_4eq.t_ww⁻¹ emissions. This represents a 198% reduction in freshwater eutrophication for the HPO system, compared to the BAU. Overall, the whole HPO supply chain emits 0.03 kgPO_4eq.t_ww⁻¹ to freshwaters, which is counterbalanced by the reduction of 0.043 kgPO_4eq.t_ww⁻¹ emissions. While the HPO production and upgrading process, comprised of the pyrolysis, condensation, and HDO, represents 61% of the EUF emissions, its use to replace HFO contributes to 7% of the EUF reduction. The major contributor to decreasing EUF (76%) corresponds to the biopesticide avoided. Moreover, despite the recovery of coproducts (except vinegar) and their application (e.g., syngas and dust combustion, biochar spreading, etc.) representing emissions of 0.007 kgPO4_eq.t_ww⁻¹ to freshwater, these emissions are almost neutralized (-0.007 kgPO_4eq.t_ww⁻¹) by the avoided heat and electricity they provide.

The bio-LNG represents higher EUF reductions than HPO, with total emission reductions of 0.09 kgPO_4eq.t_ww⁻¹. The whole supply chain induces the emission of 0.012 0.007 kgPO_4eq.t_ww⁻¹, of which the digestate management (storage and spread) is the main contributor (74%), followed by the pretreatment operations (20%). Due to the CO₂ recovery associated, the cryogenic liquefaction has a net negative EUF impact, with a reduction of 0.06 kg PO_4eq.t_ww⁻¹. Moreover, bio-LNG displaces fossil LNG, which reduces emissions by 0.025 kgPO_4eq.t_ww⁻¹. Albeit digestate represents the greatest EUF impact, it induces avoiding a mineral fertilizer, which is composed of ca. 9% phosphates (P₂O₅) and thus represents 16% fewer PO_4eq emissions.

3.1.3 Marine water eutrophication (EUM)

The whole HPO supply chain reduces this impact by 147% compared to the BAU. The HPO combustion is the major contributor to EUM, representing 84% of the total emissions. However, the main contributor to the EUM reduction is the avoided HFO, accounting for 93% of the avoided emissions. Therefore, the net balance for the onboard fuel combustion is negative, achieving emissions of -0.60 kgN_eq.t_ww⁻¹ (HPO and HFO combustion accounted). The coproducts utilization accounted by the system boundaries expansion (i.e., combustion of dust and syngas, biochar soil application, vinegar application) represents 0.06 kgN_eq.t_ww⁻¹, which are offset by the avoided services of marginal heat and electricity, as well as chemical pesticide replacement, which reduce emissions by 0.136 kgN_eq.t_ww⁻¹.

The bio-LNG scenario EUM reduction is 41% of the HPO and 60% of the EUM. While the storage and bio-LNG use did not contribute to the freshwater eutrophication represented by P emissions, the NH₃, N₂O and NOx emissions observed in these operations are contributors to the marine eutrophication represented by N. The main contributor to this impact is digestate management (storage and spread), which releases 1.31 kgN_eq.t_ww⁻¹, accounting for 55% of the positive emissions. However, the effect of digestate is partially offset by a reduction of 0.63 kgN_eq.t_ww⁻¹ resulting from avoiding mineral fertilizers. The major contribution to the EUM impact reduction (61%) compared to the BAU in the bio-LNG scenario is attributed to the fossil LNG replacement by bio-LNG.

3.1.4 Respiratory Inorganics, representing particulate matter (PM) emissions

This impact represents the impact on human health (disease incidence) by NOx, SO₂, and particulates (< 10µm and < 2.5µm) as the main pollutants. This is the only category analyzed where a SMF has worse environmental performance than the BAU. Here the bio-LNG has a positive impact on 4.9E^− 5 disease incidence whereas 1.6E^− 6 disease is avoided by ploughing the crop residues in soils (BAU). In fact, almost the whole supply chain of bio-LNG represents positive PM emissions with reductions observed only by avoiding the fossil LNG (-1.2E^− 5 disease incidence) and mineral fertilizer (-7.6E^− 6 disease incidence). The major emissions are related to the digestate management (storage and spread) accounting for 73% of the disease incidence of PM. This is explained by the high N content in digestate, which is emitted during storage and is later mineralized, relatively fast, when applied on fields.

On the opposite, the HPO scenario represents major PM disease incidence reductions compared to the BAU (-9.27x10^− 5 disease incidence). HFO is a residue like fuel, for which high SOx, NOx, and PM emissions have been attributed compared to other maritime fuels. Therefore, this impact is of major importance when analyzing the replacement of HFO by SMFs. Accordingly, the avoided combustion of HFO by implementing HPO is responsible for 97% of the 1.58E^− 4 disease incidence reduction. Likely, the HPO combustion contributes to 77% of the scenario disease incidence. The other operations represent minor flows in this impact category compared to the onboard combustion of the fuels.

3.1.5 Water scarcity

The bio-LNG shows the best performance to avoid water scarcity, which corresponds to 3.4-fold the reductions observed in the BAU. The reductions are attributed to the upgrading stage and the avoided use of fossil LNG and mineral fertilizer. These three operations, contribute almost equally to the offset of water scarcity, representing 39%, 32%, and 29% of the total reduction, respectively. The whole supply chain represents total induced water scarcity of 6.20 m³w_eq.t_ww⁻¹, of which 46% is attributed to the water addition process during the AD stage.

The HPO scenario represents approximately 50% of the reductions observed for the bio-LNG. The unit processes along the supply chain represent a positive (thus impactful) WS impact, with total consumption of 28.6 m³w_eq.t_ww⁻¹. However, the avoided products (HFO, fungicide, heat, and electricity) represent a 2.6-fold reduction of emissions, yielding a net impact of -46.9 m³w_eq.t_ww⁻¹. Of these, the avoided fungicide represents 60% of the WS reduction, followed by heat production (31%).

3.2 Overall environmental impacts and SOC implications

The results show that the SMFs have a better environmental performance for all the five impact categories as compared to the BAU scenario. The major contributors to the impacts reduction are the avoided fossil fuel combustion and the coproducts and services replaced/avoided by the system expansion. Beyond the environmental impacts assessed, this study aims to analyze the overall trade-offs between the whole environmental impacts along the supply chain and the SOC stocks maintenance achieved by returning the recalcitrant coproduct released before the upgrading process. Table 1 shows the environmental impacts scaled to the total biomass available for a C-neutral harvest of crop residues, considering the national potential of France as reported by Andrade Diaz et al., [20].

For the crop residues potential of 18.7 Mt DM.year^− 1 (13.24% water content), the BAU scenario would emit 32.17 MgCO_2eq, which are related to an average loss of 178 kt C per year as SOC (considering an annualization over 100 years). The results show, that the SMFs scenarios are both favorable in terms of SOC sequestration and climate change mitigation. For the HPO scenario, based on the SOC results, 100% of the crop residues potential can be harvested to supply the pyrolysis process with no SOC expected to decrease. Therefore, the return of biochar in the HPO scenario builds up average annual SOC stocks by 7740 kt C (considering an annualization over 100 years). while avoiding 11.91 MgCO₂eq due to the substitution of HFO by HPO. All the impacts included in the study are as well scaled to the national crop residues potential (C-neutral harvest potential), which represents a 21-fold of the results shown in Fig. 3 for the BAU and HPO scenarios.

For biogas with digestate return, the C-neutral harvest of crop residues was shown to be possible in approximately 50% of French croplands, with a national potential of 10 Mt DM.year^− 1. Accordingly, the bio-LNG has 1.7-fold the climate change mitigation potential of the HPO. Scaling the results at national level for a C-neutral harvest results in a higher mitigation potential for the HPO, which corresponds to 1.1-fold that of bio-LNG.

Table 1

Tradeoffs between SOC and whole environmental performance of the bioeconomy supply chain for producing HPO and bio-LNG to fuel the maritime industry. Results per tonne of crop residues and scaled to the C-neutral harvest potential involved for each technology, as defined in Andrade et al. [20].
		Results per tonne of crop residues			Results scaled to the national C-neutral harvest potential involved by the technology
Parameter	Units	BAU	Pyrolysis	Anaerobic Digestion	BAU	Pyrolysis ^e	Anaerobic Digestion ^{e, f}
Crop residue potential per technology ^a	Mt DM	1.00	1.00	1.00	21.18	21.18	11.32
C sequestered in soil, per year ^b	kt C	-	-	-	-178.0 ^c	7740.00	7.60
Climate change GWP100 ^d	MgCO_2 − eq	0.02	-562.50	-945.47	32.17	-11911.51	-10706.52
Eutrophication Freshwater (P)	kgPO_4 − eq	0.01	-0.01	-0.09	0.19	-0.18	-0.99
Eutrophication Marine (N)	kgN_− eq	1.08	-0.50	0.43	22.82	-10.68	4.82
Particulate matter^g formation	disease incidence	-1.63x10^− 6	-9.27x10^− 5	4.88x10^− 5	-3.45x10^− 5	-1.96x10^− 3	5.5 x10^− 4
Water scarcity	m³_w_− eq	-28.14	-46.90	-95.07	-595.87	-933.19	-1076.58

^a At the national scale of France considering 3.48 Mha of croplands, as determined using the soil-plant model STICS by Launay et al., [68] and used in Andrade-Díaz et al., [20] in AMG. A water content (w.c.) of 13.24% is considered according to [69] ^b Relative SOC sequestration within the technologies, compared to the BAU, for a 100-years’ timeframe [20] comprising the period 2020–2120. Here, the results of Andrade Diaz [20] were divided to 100 to obtain the sequestration rate per year. ^c SOC change in baseline corresponds to the difference between year 2120 and year 2020. ^d The offset potential considers that the whole supply chain CO₂ emissions related to crop residues are neutralized due to their biogenic nature according to the 0/0 methodology [46]. In other words, the CO₂ emitted along the process has a biological source being sourced from the crop residues and once emitted plants will uptake to lock the biogenic carbon cycle (ref). ^e The biomass potential and SOC sequestration accounts only for the "base" processes, namely pyrolysis and anaerobic digestion, and thus not consider the SOC effects of the upgrading technology. The environmental impacts consider the whole supply chain for the scenarios studied (HPO and bio-LNG). ^f Only Areas with no expected SOC decrease are considered. ^g in units of disease incidence per kg of PM2.5 emitted.

4.1 Potential of biofuels for the maritime sectors with regard to climate impact goals

Albeit biofuels are currently increasing their share on the road and aviation energy mix their use on the maritime sector is still limited due to a myriad of technical and policy drawbacks, e.g., engine incompatibility to combust the novel fuels in current vessels. Historically, cargo ships have been fueled by low-quality HFO, which are bottom-of-the-barrel leftover from the refining of petrol [47] entailing low costs. Accordingly, the current fleet has been designed with slow-speed propulsion systems with limited suitability to different fuels [28]. Since emissions regulations had not been put in action before the last decade [29], the maritime industry actors have continued to favor the low-cost low-quality HFO and new vessels and engines capable to carry and burn new alternative fuels are still under research and development [32]. However, the latest GHG emission reduction target set by the IMO [30] along with the 0.5% sulfur limit and the latest inclusion of the maritime industry within the emissions target of European call for immediate action to transition to renewable fuels.

The IEA [32] has estimated that lignocellulosic fuels have the potential to supply all the maritime fuel demand (455–805 Mt oil equivalent potential vs 330 Mt oil equivalent demand) while reducing the industry emissions, otherwise expected to increase by 30% in 2050 [30] Yet, there are also multiples competing demands on lignocellulosic resources, as discussed in e.g. [70]. All the environmental impacts addressed showed a better environmental performance for the SMFs scenarios than the BAU. In summary, the CC, EUM, and WS impacts were better performing for the bio-LNG, while the EUF and PM presented the most pronounced emissions reduction in the HPO scenario.

Approximately 137% and 162% GHG emission reduction can be attained if crop residues are harvested and transformed to HPO and bio-LNG, and used to substitute HFO and LNG, respectively. These tremendous emissions savings are mainly related to the avoided mineralization of crop residues on fields, which would else be released as CO₂, and by the replacement of the fossil counterpart fuel as well as the marginal heat, electricity and fertilizer/pesticides currently used. In this study, we considered an optimistic energetic performant future, where all the energy services (heat and electricity) are electrified. If more conventional sources of heat would else be used (and replaced), the emission reduction would be even larger, as more heat is produced than used.

In fact, compared to the fossil alternatives the SMF represent over 90% less CO_2 − eq emissions. The HPO combustion represents a 98% reduction of GHG emissions as compared to the HFO. Likely, the combustion of bio-LNG represents 92% less CO_2eq emissions than the fossil alternative. Our results are in accordance with previous studies, where it has been reported that approximately 50 to 90% of the life cycle impacts are related to the avoided fossil alternative [71], highlining the ability of bio-LNG to reduce 90% of the fossil LNG GHG emissions [72].

Besides GHG emissions, the maritime industry is responsible for NOx, SOx, and PM emissions [33], which represents a main environmental risk. Therefore, the marine water eutrophication (N) and particulate matter (NOx, SOx, and PM) impacts are of key importance in the maritime transport’s context. Replacing HFO with HPO, reduces the PM impact by 67% and the marine eutrophication by 33%. Likely, transitioning to bio-LNG shows 36% less PM impact and 24% less marine eutrophication.

4.2 Trade-offs with SOC sequestration

Both the HPO and bio-LNG allow recovering a C-rich coproduct, deemed as recalcitrant [66,73], that can be applied on soils as C amendment, namely biochar and digestate, respectively. Nonetheless, the different nature of both products was considered within the modeled LCA, producing contrasting results for each. Biochar, which is composed by 95% recalcitrant carbon (i.e., degradation resistant carbon) is expected to heavily remain in soils, i.e. 75% of its C after 100 years [66]. This represented 82% of the GHG emission reduction for the HPO scenario. However, it does not affect any of the other four impact categories.

On the other hand, digestate has been reported to have a behavior similar to crop residues [74,75] with the difference that the labile fraction responsible of the major share of CO₂ emissions in the BAU has been removed and converted to biogas. The recalcitrant carbon fraction of digestate has a short mean residence time (ca. 1.2 years) associated [66]. Moreover, the nitrogen content in the digestate is concentrated during the AD process (as other fractions are lost to the gas phase), while the ratio inorganic : organic N is enhanced as a result of the process, granting fertilizing properties [76]. Results show that digestate is the major contributor in four of the five impacts investigated for the bio-LNG scenario. For instance, the digestate mineralization during storage and on field is responsible of 55% of the positive CO_2eq emissions (not through CO₂, but CH₄ and N₂O losses), 58% of the eutrophication of marine water, 75% eutrophication of freshwater, and 73% of particulate matter formation in the bio-LNG scenario. These emissions are directly related to either the high N and P content of digestate.

However, although digestate contribute to the major share of emissions in the bio-LNG scenario, these are offset by the reduced and avoided overall emissions along the whole supply chain. Aligned with the aim of this study, we have compared the trade-off of the C-neutral harvest of the crop residues to produce the SMFs and the full environmental impacts associated.

Scaling the environmental impacts of one wet tonne of crop residues to the national C-neutral harvest potential of each technology in France (Table 1), shows that HPO is the most environmentally performant scenario both in terms of emissions and SOC sequestration. Interestingly, the bio-LNG potential to offset water scarcity and freshwater eutrophication is 5.5-and 1.15-fold that of HPO, even when harvesting only half the same amount of crop residues. Overall, Table 1 does not show any trade-offs between the addressed environmental impacts and SOC stocks maintenance for the investigated SMFs scenarios. The C-neutral harvest of crop residues thus pose major environmental savings if the recalcitrant coproducts are returned to soils, allowing to not simply maintain SOC stocks, but to improve them.

The LCA results reveal, that the precautionary practice of leaving the crop residues on soils results in higher GHG emissions than valorizing the residues for biofuel production. This also applies for all other environmental impacts addressed. Harvesting crop residues to produce biofuels, here HPO and bio-LNG for maritime use, while ensuring the return of the C-rich coproducts to soils is a win-win option because it allows to sequester C in soils, provide the energy service to displace fossil fuels, and consequently reduce the overall GHG emissions along with other environmental impacts of the system.

Despite the bio-LNG scenario is environmentally performant to reduce C-related emissions, digestate is held responsible of major N losses, including N₂O, NH₃, and nitrate losses to water. This is critically detrimental for the overall scenario performance because N₂O represent almost 300 times the global warming potential of CO₂. It is also detrimental to other impacts, most importantly the marine eutrophication (Table 1), being one of the two impacts where a net positive impact is observed. Therefore, measures to reduce the soil-denitrification induced by digestate application need to be addressed. As the N₂O result from the nitrification and oxidation of ammonium, already existing techniques such as nitrification inhibitors can be used [77]. Other techniques regarding microbial enrichment [78] and farming management activities (e.g., tillage, irrigation) [79] can be implemented in order to offset the N-flux contribution from digestate. Techniques such as digestate acidification at the spreading stage can also limit nitrogen losses (here NH₃) and hence reduce the marine eutrophication impact. Moreover, biochar has well recognized N-offset properties [80] and could be applied in tandem with digestate to create synergies from the nutrient-fertilizer effect of digestate and reduced C and N mineralization from biochar.

4.3 Key aspects to consider

Though comparing the renewable fuels vs the fossil ones, HPO shows a better environmental performance than fossil HFO, bio-LNG exhibits less overall emission along the whole supply chain, per wet tonne of crop residue. This is in part explained because the system modeled in this study considers that the cryogenic upgrading allows separating a CO₂ stream, which can then be recovered to avoid the production of fossil derived CO₂ for the chemical industry. In fact, avoiding this fossil-derived CO2 has a significant impact (~ 0.9 kgCO_2e per kg fossil CO₂ avoided). However, it remains unclear to which extent a 100% recovery can be considered representative of future biogas plants as the recovery efficiency could be lower. Moreover, the biogas injection to the cryogenic liquefaction process may entail some gas slips [64] that were considered negligible herein (yet, losses were considered at the moment to inject the non-upgraded biogas to the biogas pipelines transporting the gas to the upgrading site).

In fact, fossil LNG has been promoted to reduce GHG emissions in the maritime sector compared to other fossil fuels. However, this characteristic is counterpoised by the risk of slipping CH₄ while processing the natural gas, which has a global warming potential 30 times that of CO₂. It has been determined that a 3.5% natural gas slip on ship operation, may result in 3 to 9% higher emissions than HFO. Therefore, it is crucial to evaluate the possible fugitive losses during the LNG production process [81]. The fossil LNG used from Ecoinvent 3.9.1, assumes an 8.6% natural gas consumption to run the liquefaction process, a 0.05% gas leakage, and that all the CO₂ separated is emitted. These assumptions are fundamentally different than those consider in the bio-LNG scenario, where we have considered an optimized future in terms of energy performance, and the full recovery of the separated CO₂. However, as we considered a bio-LNG driven future where the biogas is transported through a dedicated pipeline to the upgrading facilities located next to the harbor port, we penalized the upgrading process by assuming a total 1.70% leakage due to the pipeline injection, and upgrading operation. In order to have transparent comparisons, it is necessary to consider the same leakage assumptions for the fossil and biofuel scenarios, which could be considered in further sensitivity analyses.

The cryogenic upgrading of biomethane is still limited due to technology development issues, high costs, and high energy consumption to comply with the cryogenic process requirements [82]. However, according to the Danish Energy Agency [64], this technology may develop in future years due to the lower energy costs envisioned at commercial scale, high purity of the biomethane, expected leakages below 1%, and possibility to recover coproducts such as CO₂ and N.

Regarding the HPO process, pyrolysis oil is not considered a drop-in fuel due to the lack of compliance with fuels standards (e.g., high water content, high O₂ content, acidity). However, when upgraded, the stabilized oil, here HPO, is an attractive biofuel for the sea transport able to replace HFO with notorious reduced emissions in multiple impact categories. Nonetheless, fast pyrolysis remains at a pioneer stage and the potential development of this technology at commercial scale is still uncertain [64]. Moreover, one critique that detracts the hydrodeoxygenation performance is the high requirement of H₂, which can represent 15% [49,52] of the produced biofuel and is mainly supplied by steam reforming of fossil fuels [55]. Here, we modeled the production of the H₂ by means of alkaline electrolysis [41]. One consequential benefit of using electrolysis-derived H₂ is the ability to recover O₂, which can reach up to 95% of efficiency. However, to remain conservative, we considered no O₂ recovery in this study. Recovering and substituting conventional O₂ could increase the environmental performance of the HPO scenario and could be analyzed in further sensitivity analyses.

The analysis of the LCA results observed here coupled to the SOC stocks simulations allows inferring that harvesting the crop residues to supply the bioeconomy, followed by the return of the recalcitrant coproducts to soils, allows to not only maintain, but to improve the soils C budget, while at the same time triggering emission reduction for the climate change, marine and freshwater eutrophication, particulate matter, and water scarcity environmental impact by replacing fossil fuels and marginal energy (i.e., electricity and heat).

For the particular case of HPO and bio-LNG studied in here, these biofuels have the potential to offset over 90% of the GHG emissions produced by the combustion of the traditional fossil HFO and LNG. In particular, HPO is of key interest to reduce the particulate matter impact of HFO by 67%, associated to NOx, SOx, and PM emissions, which is a key issue in the sea transport mitigation goals. Similarly, bio-LNG has the highest potential to reduce freshwater eutrophication, climate change, and water scarcity if the whole system is considered. The results show that managing crop residues by just ploughing them back to soils, does not only hamper the biomass supply to the bioeconomy, but also results in higher environmental impacts as well as lower SOC stocks.

However, the validity of our study relies on the transparency and representativeness of the data used in the models. Current LCI data related to maritime biofuels are still sparse, and existing studies are often not directly comparable, which complicates a further in-depth assessment of a full well-to-wake LCA for the sea transport industry. In the perspective of decision-making, results shown here must be considered under the umbrella of a further sensitivity and uncertainty analysis to shed light on the sensitive and uncertain parameters the model involved.

Data availability

This manuscript is supported by a supplementary information document and the LCI foreground database is openly available in “TBI - Toulouse Biotechnology Institute - T21018” at https https://doi.org/10.48531/JBRU.CALMIP/1JXQK3 [43].

Supporting documents and data

The supplementary information accompanying this paper is presented in Appendix A4a.

The authors declare no conflicts of interest.

Energy & Climate Intelligence Unit. Net zero emissions race. 2022 Scorecard [Internet]. Net Zero Scorecard. 2022 [cited 2022 Feb 27]. Available from: https://eciu.net/netzerotracker
Department for Business, Energy & Industrial Strategy. Net Zero Strategy: Build Back Greener. UK: HM Government UK; 2021 Oct. (Climate Change Act).
Energy Transitions Commission. China 2050: A fully developed rich zero-carbon economy [Internet]. China: Energy Transitions Commission; 2019. Available from: https://www.energy-transitions.org/publications/china-2050-a-fully-developed-rich-zero-carbon-economy
European Comission. Regulation (EU) 2021/1119 of the European Parliament and of the Council of 30 June 2021 establishing the framework for achieving climate neutrality and amending Regulations (EC) No 401/2009 and (EU) 2018/1999 (‘European Climate Law’). PE/27/2021/REV/1 [Internet]. 2021. Available from: http://data.europa.eu/eli/reg/2021/1119/oj
IEA. Net Zero by 2050 – A roadmap for the Global Energy Sector [Internet]. IEA; 2021 [cited 2023 May 3]. Available from: https://www.iea.org/reports/net-zero-by-2050
IPCC. Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. IPCC; 2018.
Blanco-Canqui H. Crop Residue Removal for Bioenergy Reduces Soil Carbon Pools: How Can We Offset Carbon Losses? Bioenerg Res. 2013;14.
Katherine Rodriguez Caceres, Francy Blanco Patino, Julian Araque Duarte, Viatcheslav Kafarov. Assessment of the energy potential of agricultural residues in non-interconnected zones of colombia: case study of choco and putumayo. Chemical Engineering Transactions. 2016 Jun;50:349–54.
Carvalho JLN, Hudiburg TW, Franco HCJ, DeLucia EH. Contribution of above‐ and belowground bioenergy crop residues to soil carbon. GCB Bioenergy. 2017 Aug;9(8):1333–43.
Lal R. Soil carbon sequestration to mitigate climate change. Geoderma. 2004 Nov 1;123(1):1–22.
Meyer RS. Potential impacts of climate change on soil organic carbon and productivity in pastures of south eastern Australia. Agricultural Systems. 2018;13.
Paustian K, Larson E, Kent J, Marx E, Swan A. Soil C Sequestration as a Biological Negative Emission Strategy. Front Clim. 2019 Oct 16;1:8.
Autret B, Mary B, Chenu C, Balabane M, Girardin C, Bertrand M, et al. Alternative arable cropping systems: A key to increase soil organic carbon storage? Results from a 16 year field experiment. Agriculture, Ecosystems & Environment. 2016 Sep;232:150–64.
Mondini C, Cayuela ML, Sinicco T, Fornasier F, Galvez A, Sánchez-Monedero MA. Soil C Storage Potential of Exogenous Organic Matter at Regional Level (Italy) Under Climate Change Simulated by RothC Model Modified for Amended Soils. Front Environ Sci. 2018 Nov 29;6:144.
Fujisaki K, Chevallier T, Chapuis-Lardy L, Albrecht A, Razafimbelo T, Masse D, et al. Soil carbon stock changes in tropical croplands are mainly driven by carbon inputs: A synthesis. Agriculture, Ecosystems & Environment. 2018 May 1;259:147–58.
Scarlat N, Fahl F, Lugato E, Monforti-Ferrario F, Dallemand JF. Integrated and spatially explicit assessment of sustainable crop residues potential in Europe. Biomass and Bioenergy. 2019 Mar 1;122:257–69.
Fischer G, Prieler S, van Velthuizen H, Berndes G, Faaij A, Londo M, et al. Biofuel production potentials in Europe: Sustainable use of cultivated land and pastures, Part II: Land use scenarios. Biomass and Bioenergy. 2010 Feb;34(2):173–87.
Monforti F, Lugato E, Motola V, Bodis K, Scarlat N, Dallemand JF. Optimal energy use of agricultural crop residues preserving soil organic carbon stocks in Europe. Renewable and Sustainable Energy Reviews. 2015 Apr 1;44:519–29.
Hansen JH, Hamelin L, Taghizadeh-Toosi A, Olesen JE, Wenzel H. Agricultural residues bioenergy potential that sustain soil carbon depends on energy conversion pathways. 2020;12.
Andrade Díaz C, Clivot H, Albers A, Zamora-Ledezma E, Hamelin L. The crop residue conundrum: Maintaining long-term soil organic carbon stocks while reinforcing the bioeconomy, compatible endeavors? Applied Energy. 2023 Jan 1;329:120192.
Woolf D, Lehmann J. Modelling the long-term response to positive and negative priming of soil organic carbon by black carbon. Biogeochemistry. 2012;13.
Lefebvre D, Williams A, Meersmans J, Kirk GJD, Sohi S, Goglio P, et al. Modelling the potential for soil carbon sequestration using biochar from sugarcane residues in Brazil. Sci Rep. 2020 Dec;10(1):19479.
Zhang Q, Xiao J, Xue J, Zhang L. Quantifying the Effects of Biochar Application on Greenhouse Gas Emissions from Agricultural Soils: A Global Meta-Analysis. Sustainability. 2020 Apr 23;12(8):3436.
Stella T, Mouratiadou I, Gaiser T, Berg-Mohnicke M, Wallor E, Ewert F, et al. Estimating the contribution of crop residues to soil organic carbon conservation. Environmental Research Letters. 2019 Sep 6;14(9):094008.
France Agrimer. L´Observatoire National des Ressources en Biomasse. Évaluation des ressources agricoles et agroalimentaires disponibles en France – édition 2020. Agrimer; 2020.
SSI. Defining sustainability criteria for marine fuels: Fifteen issues, principles and criteria for zero and low carbon fuels for shipping [Internet]. The sustainable Shipping Initiative and Copenhagen Business School Maritime; 2021. Available from: https://www.sustainableshipping.org/wp-content/uploads/2021/09/Defining-sustainability-criteria-for-marine-fuels.pdf
Hsieh C wen C, Felby C. Biofuels for the marine shipping sector> An overview and analysis of sector infrastructure, fuel technologies and regulations. IEA Bioenergy; 2017. (Task 39).
United Nations. Review of Maritime transport 2022: Navigating stormy waters. Geneva: United Nations; 2022. 174 p. (Review of maritime transport / United Nations Conference on Trade and Development, Geneva).
European Union Parliament. Fit for 55 package. 2021.
Index of MEPC Resolutions and Guidelines related to MARPOL Annex VI [Internet]. [cited 2023 May 10]. Available from: https://www.imo.org/en/OurWork/Environment/Pages/Index-of-MEPC-Resolutions-and-Guidelines-related-to-MARPOL-Annex-VI.aspx
European Union Parliament. REGULATION OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL amending Regulation (EU) 2015/757 in order to provide for the inclusion of maritime transport activities in the EU Emissions Trading System and for the monitoring, reporting and verification of emissions of additional greenhouse gases and emissions from additional ship types. PE-CONS 10/23 Apr 20, 2023.
Simonsen TI, Weiss ND, van Dyk S, van Thuijl E, Thomsen ST, Thomsen EST. Progress towards biofuels for marine shipping. IEA Bioenergy; 2021. (Task 39).
IMO. Fourth IMO GHG Study 2020 [Internet]. IMO; 2020. Available from: https://wwwcdn.imo.org/localresources/en/OurWork/Environment/Documents/Fourth%20IMO%20GHG%20Study%202020%20-%20Full%20report%20and%20annexes.pdf
MARPOL. RESOLUTION MEPC.304(72) INITIAL IMO STRATEGY ON REDUCTION OF GHG EMISSIONS FROM SHIPS. MEPC 72/17/Add.1 2018.
MARPOL. MEPC RESOLUTION.366(79) INVITATION TO MEMBER STATES TO ENCOURAGE VOLUNTARY COOPERATION BETWEEN THE PORT AND SHIPPING SECTORS TO CONTRIBUTE TO REDUCING GHG EMISSIONS FROM SHIPS. MEPC 79/15/Add.1 2022.
ISO. ISO 14040:2006 [Internet]. ISO. 2014 [cited 2023 May 10]. Available from: https://www.iso.org/fr/standard/37456.html
ISO. ISO 14044:2006 [Internet]. ISO. 2014 [cited 2023 May 10]. Available from: https://www.iso.org/fr/standard/38498.html
Brandão M, Martin M, Cowie A, Hamelin L, Zamagni A. Consequential Life Cycle Assessment: What, How, and Why? In: Abraham MA, editor. Encyclopedia of Sustainable Technologies [Internet]. Oxford: Elsevier; 2017 [cited 2023 May 10]. p. 277–84. Available from: https://www.sciencedirect.com/science/article/pii/B9780124095489100685
Su-ungkavatin P. Assessing the environmental performance of future sustainable aviation systems: methodological development and evaluation by life cycle assessment. [France]: INSA Toulouse; 2022.
Brassard P, Godbout S, Hamelin L. Framework for consequential life cycle assessment of pyrolysis biorefineries: A case study for the conversion of primary forestry residues. Renewable and Sustainable Energy Reviews. 2021 Mar;138:110549.
Javourez U. Transforming residual biomass into food and feed – Towards an LCA optimization platform. [France]: INSA Toulouse; 2023.
Ecoinvent. Ecoinvent 3.9.1 database. 2022.
Andrade Díaz C. Database: LCIs for : To harvest or not? Tradeoffs between SOC maintenance and overall environmental performance of harvesting crop residues for the bioeconomy. Datavers.Callisto; 2023.
European Comission. COMMISSION RECOMMENDATION of 16.12.2021 on the use of the Environmental Footprint methods to measure and communicate the life cycle environmental performance of products and organisations [Internet]. 2021. Available from: https://environment.ec.europa.eu/system/files/2021-12/Commission%20Recommendation%20on%20the%20use%20of%20the%20Environmental%20Footprint%20methods_0.pdf
Steubing B, de Koning D, Haas A, Mutel CL. The Activity Browser — An open source LCA software building on top of the brightway framework. Software Impacts. 2020 Feb 1;3:100012.
Cucurachi S, Steubing B, Siebler F, Navarre N, Caldeira C, Sala S. Prospective LCA methodology for Novel and Emerging Technologies for BIO-based products - The PLANET BIO project [Internet]. JRC Publications Repository. 2022 [cited 2023 May 15]. Available from: https://publications.jrc.ec.europa.eu/repository/handle/JRC129632
Comer B, Olmer N, Mao X, Roy B, Rutherford D. Prevalence of heavy fuel oil and black carbon in Arctic shipping, 2015 to 2025. International Council on Clean Transportation; 2017.
Oasmaa A, Lehto J, Solantausta Y, Kallio S. Historical Review on VTT Fast Pyrolysis Bio-oil Production and Upgrading. Energy Fuels. 2021 Apr 1;35(7):5683–95.
Vienescu DN, Wang J, Le Gresley A, Nixon JD. A life cycle assessment of options for producing synthetic fuel via pyrolysis. Bioresource Technology. 2018 Feb 1;249:626–34.
Sorunmu Y, Billen P, Spatari S. A review of thermochemical upgrading of pyrolysis bio-oil: Techno-economic analysis, life cycle assessment, and technology readiness. GCB Bioenergy. 2020;12(1):4–18.
Peters JF, Iribarren D, Dufour J. Biomass Pyrolysis for Biochar or Energy Applications? A Life Cycle Assessment. Environ Sci Technol. 2015 Apr 21;49(8):5195–202.
Iribarren D, Peters JF, Dufour J. Life cycle assessment of transportation fuels from biomass pyrolysis. Fuel. 2012 Jul 1;97:812–21.
Emery I, Dunn JB, Han J, Wang M. Biomass Storage Options Influence Net Energy and Emissions of Cellulosic Ethanol. Bioenerg Res. 2015 Jun 1;8(2):590–604.
Brassard P. Mass balance and LCA inventory of bio-oil production by fast pyrolysis of wheat straw. Unpublished study, received as a courtesy from the authors. 2022;
Jones S, Meyer P, Snowden-Swan L, Padmaperuma A, Laboratory PNN. Process Design and Economics for the Conversion of Lignocellulosic Biomass to Hydrocarbon Fuels: Fast Pyrolysis and Hydrotreating Bio-oil Pathway. 2013;97.
Elliott DC. Transportation fuels from biomass via fast pyrolysis and hydroprocessing. WIREs Energy and Environment. 2013;2(5):525–33.
Aronietis R, Sys C, van Hassel E, Vanelslander T. Forecasting port-level demand for LNG as a ship fuel: the case of the port of Antwerp. Journal of Shipping and Trade. 2016 Jul 20;1(1):2.
Pellegrini LA, De Guido G, Langé S. Biogas to liquefied biomethane via cryogenic upgrading technologies. Renewable Energy. 2018 Aug 1;124:75–83.
Florio C, Fiorentino G, Corcelli F, Ulgiati S, Dumontet S, Güsewell J, et al. A Life Cycle Assessment of Biomethane Production from Waste Feedstock Through Different Upgrading Technologies. Energies. 2019 Jan;12(4):718.
Hamelin L, Naroznova I, Wenzel H. Environmental consequences of different carbon alternatives for increased manure-based biogas. Applied Energy. 2014 Feb;114:774–82.
Tonini D, Hamelin L, Astrup TF. Environmental implications of the use of agro-industrial residues for biorefineries: application of a deterministic model for indirect land-use changes. GCB Bioenergy. 2016;8(4):690–706.
Symons GE, Buswell AM. The Methane fermentation of carbohydrates. Journal of the American Chemical Society. 1933;
Yousef AM, El-Maghlany WM, Eldrainy YA, Attia A. Upgrading biogas to biomethane and liquid CO2: A novel cryogenic process. Fuel. 2019 Sep 1;251:611–28.
Danish Energy Agency, Energinet. Technology Data. Renewable fuels. [Internet]. 2017. Available from: http://www.ens.dk/teknologikatalog
Carvalho F, O’Mally J, Osipova L, Pavlenko N. Keu issues in LCA methodology for marine fuels. ICCT; 2023 Apr.
Andrade C, Albers A, Zamora-Ledezma E, Hamelin L. A review on the interplay between bioeconomy and soil organic carbon stocks maintenance. PREPRINT (version 2) available at Research Square [Internet]. 2022 Mar 16 [cited 2022 Mar 16]; Available from: https://www.researchsquare.com
Lehmann J, Cowie A, Masiello CA, Kammann C, Woolf D, Amonette JE, et al. Biochar in climate change mitigation. Nat Geosci. 2021 Dec;14(12):883–92.
Launay C, Constantin J, Chlebowski F, Houot S, Graux A, Klumpp K, et al. Estimating the carbon storage potential and greenhouse gas emissions of French arable cropland using high‐resolution modeling. Glob Change Biol. 2021 Apr;27(8):1645–61.
Karan S. Cambioscop RO1: Dataset on characterization, quantity and current use of French residual biomasses. 2022 Nov 28 [cited 2023 May 10];1. Available from: https://data.mendeley.com/datasets/b9sx3h3584
Su-ungkavatin P, Tiruta-Barna L, Hamelin L. Biofuels, electrofuels, electric or hydrogen?: A review of current and emerging sustainable aviation systems. Progress in Energy and Combustion Science. 2023 May 1;96:101073.
Al-Enazi A, Okonkwo EC, Bicer Y, Al-Ansari T. A review of cleaner alternative fuels for maritime transportation. Energy Reports. 2021 Nov 1;7:1962–85.
Hacatoglu K, McLellan PJ, Layzell DB. Production of Bio-Synthetic Natural Gas in Canada. Environ Sci Technol. 2010 Mar 15;44(6):2183–8.
Gómez N, Rosas JG, Singh S, Ross AB, Sánchez ME, Cara J. Development of a gained stability index for describing biochar stability: Relation of high recalcitrance index (R50) with accelerated ageing tests. Journal of Analytical and Applied Pyrolysis. 2016 Jul;120:37–44.
Möller K. Effects of anaerobic digestion on soil carbon and nitrogen turnover, N emissions, and soil biological activity. A review. Agron Sustain Dev. 2015 Jul;35(3):1021–41.
Thomsen IK, Olesen JE, Møller HB, Sørensen P, Christensen BT. Carbon dynamics and retention in soil after anaerobic digestion of dairy cattle feed and faeces. Soil Biology and Biochemistry. 2013 Mar;58:82–7.
Alburquerque JA, de la Fuente C, Campoy M, Carrasco L, Nájera I, Baixauli C, et al. Agricultural use of digestate for horticultural crop production and improvement of soil properties. European Journal of Agronomy. 2012 Nov;43:119–28.
De Notaris C, Abalos D, Mikkelsen MH, Olesen JE. Potential for the adoption of measures to reduce N2O emissions from crop residues in Denmark. Science of The Total Environment. 2022 Aug 20;835:155510.
Jonassen KR, Hagen LH, Vick SHW, Arntzen MØ, Eijsink VGH, Frostegård Å, et al. Nitrous oxide respiring bacteria in biogas digestates for reduced agricultural emissions. ISME J. 2022 Feb;16(2):580–90.
Hassan MU, Aamer M, Mahmood A, Awan MI, Barbanti L, Seleiman MF, et al. Management Strategies to Mitigate N2O Emissions in Agriculture. Life (Basel). 2022 Mar 17;12(3):439.
Wu D, Ren C, Ren D, Tian Y, Li Y, Wu C, et al. New insights into carbon mineralization in tropical paddy soil under land use conversion: Coupled roles of soil microbial community, metabolism, and dissolved organic matter chemodiversity. Geoderma. 2023 Apr 1;432:116393.
Baresic D, Smith T, Raucci C, Rehmatulla N, Narula K, Rojon I. LNG as a marine fuel in the EU: Market, bunkering infrastructure investments and risks in the context of GHG reductions. London: UMAS - Transport and Environment; 2018.
Naquash A, Qyyum MA, Chaniago YD, Riaz A, Yehia F, Lim H, et al. Separation and purification of syngas-derived hydrogen: A comparative evaluation of membrane- and cryogenic-assisted approaches. Chemosphere. 2023 Feb 1;313:137420.

Also in Chap. 4 of this thesis.

The Appendix is not available with this version

Download PDF

Version 1

posted

You are reading this latest preprint version

To harvest or not? Tradeoffs between SOC maintenance and overall environmental performance of harvesting crop residues for the bioeconomy

Status:

Version 1

Abstract

Figures

1. Introduction

2. Methods

2.1 Life cycle assessment implementation

2.2 Case scenarios description

2.2.1 Pyrolysis scenario: Hydrotreated pyrolysis oil (HPO)

2.2.2 Anaerobic Digestion (AD) scenario: Cryogenic liquefied biomethane (bio-LNG)

2.3 System boundaries

3. Results

3.1 Analysis per environmental impact

3.1.1 Climate change

3.1.2 Freshwater eutrophication (EUF)

3.1.3 Marine water eutrophication (EUM)

3.1.4 Respiratory Inorganics, representing particulate matter (PM) emissions

3.1.5 Water scarcity

3.2 Overall environmental impacts and SOC implications

4. Discussion

4.1 Potential of biofuels for the maritime sectors with regard to climate impact goals

4.2 Trade-offs with SOC sequestration

4.3 Key aspects to consider

5. Conclusion

Declarations

References

Footnotes

Appendix

Status:

Version 1