The International Journal of Life Cycle Assessment https://doi.org/10.1007/s11367-023-02152-2 BUILDING COMPONENTS AND BUILDINGS Environmental assessment of a new building envelope material derived from urban agriculture wastes: the case of the tomato plants stems Pere Llorach‑Massana1,2 · Laura Cirrincione3 · Jorge Sierra‑Perez4,5 · Gianluca Scaccianoce3 · Maria La Gennusa3 · Javier Peña2 · Joan Rieradevall1,6 Received: 9 June 2022 / Accepted: 27 February 2023 © The Author(s) 2023 Abstract Purpose Decarbonizing cities is one of today’s biggest challenges. In this regard, particular attention has been paid on improving the environmental performance of buildings. In this framework, this work consists in assessing the environmental impact of an innovative building envelope component derived from urban agriculture (UA) wastes. In fact, rooftop UA seems to be a possible solution to the rising food demand due to increasing urban demographic growth. Consequently, rooftop UA wastes need to be treated in sustainable ways. Methods This study aims to determine the carbon footprint and embodied energy of a new infill wall material, derived from UA wastes produced by a building rooftop greenhouse tomato crop, and evaluate the potential biogenic carbon that such by-product could fix temporally until its end of life. After an initial description of the manufacturing process of the new material, its carbon footprint and embodied energy have been calculated by means of the life cycle assessment (LCA) methodology according to the ISO 14044 and the ISO 14067 guidelines adapted to the analyzed context. In particular, the inventory analysis is based on data collected from the production of samples of the new material at the laboratory scale. Results and discussion The results of the LCA indicate that, when the biogenic carbon fixed in the UA wastes is considered, a negative carbon footprint of − 0.2 kg C ­ O2 eq. per kg of material can be obtained. Hence, it can be assumed that from a life cycle perspective the material is able to fix carbon emissions instead of emitting them. Specifically, for the considered sce- nario, approximately 0.42 kg ­CO2 eq./m2 per year could be sequestered. However, the crop area required to produce enough waste to manufacture a unit of material is quite high. Therefore, future studies should focus on individuate solutions to reduce the density of the new component, and also different urban crops with higher waste production rates. Conclusions The outcomes of the study put in evidence the potential of the new proposed infill wall component in fixing carbon emissions from UA, allowing to also compensate those relating to the production and transportation stages of the component life cycle. Moreover, producing by-products with UA wastes, hence temporally storing the carbon fixed by crops, may contribute to reduce the carbon cycles speed conversely to traditional waste management solutions, other than lower new raw materials depletion. Keywords Innovative building envelope components · Infill wall material · Urban agriculture wastes · Biogenic carbon · Carbon footprint · LCA · Embodied energy 1 Introduction climate change scenarios (UNFCCC 2021; Finkbeiner and Bach 2021). It is, indeed, well evident how in the last few Decarbonized urban environments are crucial items for a decades cities have been increasingly affected by different future that is environmentally sustainable, energy resil- types of threats, i.e. natural shocks (e.g., heatwaves, floods), ient and economically viable within the current and future climate change and intensification in migratory flows (long- term stresses); the negative impacts of which they are quite Communicated by Vanessa Bach. often unable to cope (UCCRN 2018; Buggin et al. 2019). More recently, the pandemic (Covid19) and energy-economic * Laura Cirrincione laura.cirrincione@unipa.it crises (Ukraine-Russia conflict) have even more highlighted the need for a more sustainable and self-sufficient urban Extended author information available on the last page of the article 13 Vol.:(0123456789) The International Journal of Life Cycle Assessment metabolism, while still aimed at mitigating climate change use of renewable energy sources) aimed at accomplishing (Ipsen et al. 2019; Salvia et al. 2021). Urban settlements, in energy efficiency (Cirrincione et al. 2019; Li et al. 2021; fact, are subjected to a constant process of urbanization linked Nutkiewicz et al. 2021) and economic savings (Manfren to demographic variations (Massacritica 2015; UN 2019) et al. 2022, 2021b), while also enhancing citizens comfort, that requires an uninterrupted supply of food, materials and health and wellbeing (ENEA 2020b; Cirrincione e al. 2020b; energy, releasing just as many atmospheric pollutants (IEA Kousis and Pisello 2020). Therefore, some aspects need to 2019a; EEA 2020). In 2018, 55.3% of the world population be further investigated in order to push forward urban build- was estimated residing in urbanized areas, compared to 30% ing decarbonization by also including passive measures in in 1950, and it is predicted that by 2050 the percentage will the picture (Cirrincione et al. 2020c; Napoli et al. 2022). rise to 66% (Massacritica 2015; UN 2019; Santamouris 2020). This opens up an opportunity to rethink the passive energy All these aspects implicate a constant change of cities, performance of buildings. Specifically, an accurate design affecting the performance of public and private buildings of the external envelopes (which constitute a relevant part of within them. In fact, according to recently released bulletins a building), aimed at reducing their environmental impact, on energy consumption and related pollutant emissions, the should properly take into account the construction character- building sector accounts for 25–40% of the overall energy use istics, the climatic context in which buildings are located and at global, European and Italian levels, corresponding to shares the possibility of employing local waste for the production of of energy-related C ­ O2 emissions comprised between 17.5% innovative materials, so as to also reduce the environmental and 39% (Tsemekidi et al. 2020; ENEA 2020a; IEA 2019b). impacts related to waste management and its transportation In this regard, recent initiatives, regulations and economic (Jeswani et al. 2013; Cirrincione et al. 2022). Consequently, bonuses, concerning urban sustainability issued at global, Euro- the environmental, energy and economic benefits and limi- pean and national levels, place particular attention on improv- tations of synthetic and renewable/natural materials used ing the energy and environmental performance of buildings in for the envelope have been extensively analyzed in the lit- order to enhance urban resilience to climate change. On this erature focusing the attention to the use phase of buildings subject, the UN Sustainable Development Goals—SDGs (spe- (Ferrante et al. 2016; Rodrigues et al. 2017; Capitano et al. cifically, “Goal 11—Make cities and human settlements inclu- 2017; Capitano et al. 2022). sive, safe, resilient and sustainable”, “Goal 12—Responsible However, in addition to the operational one the overall consumption and production” and “Goal 13—Climate action”) energy related to a building also includes its embodied one, (UN 2015a) and 2030 Agenda for Sustainable Development which is the energy sequestered by all the materials compos- (UN 2015b), the EU climate-energy frameworks, long-term ing a building throughout its entire life cycle from produc- strategies (European Commission 2014; European Commission tion to disposal (Pacheco-Torgal et al. 2012; Pacheco-Torgal 2018) and Recovery Plan Next-Generation EU (European 2014; Kiss et al. 2022), and that therefore should not be Commission 2020) are just a few to be cited. Along with those overlooked. As it has already been demonstrated, indeed, expressly intended for buildings, i.e. the EU Ecolabel for build- one of the most influential components in the environmental ings products (Peri and Rizzo 2012; Capitano et al. 2014; EU performance of buildings (both in the construction and use 2017; Cirrincione et al. 2020a) and the Energy performance phases) is represented by the envelope, which could reach of Building Directives—EPBD (European Union 2010; 30 to 50% of the embodied energy depending on the used European Union 2012); the latter, in particular, introduce the material (Sierra-Pérez et al. 2016a, 2016b). concept of nearly zero-energy (NZE) buildings according to To achieve carbon neutrality, therefore, appropriate decar- which the energy required to meet the needs of buildings should bonization strategies are needed. More in detail, according be extensively covered by renewable sources produced on site to some of the most established decarbonization approaches or nearby. That is why, promote and assess the feasibility of (Andrews 2014; UNFCCC 2021), the path towards carbon initiatives aimed at improving resilience (Berardi and Jafarpur neutrality entails different actions ranging from avoiding 2020; Cirrincione et al. 2021) and foster the sustainability of the carbon intensive activities, to reducing the use of traditional built environment (Bisegna et al. 2019; Manfren et al. 2021a), (fossil-fuel-based) raw materials and energy sources and/ on smaller and bigger scales (Guerrieri et al. 2019), represent or replacing them with natural, renewable or waste-derived some of the major commitments/challenges of the last decades alternatives, to balancing and compensating the unavoidable for scientific communities in order to increase decarbonization emissions (Fabbri et al. 2020; Ferrante et al. 2015; La Gennusa to mitigate and combat climate change (Nastasi 2022). et al. 2017; Lu et al. 2021). In this framework, the concepts of climate and carbon At the same time, the demographic growth experienced neutrality have lately been increasingly applied to both new in recent decades has led to a growing food demand as well, and old buildings since they constitute a predominant com- which will tend to furtherly increase in the near future. As ponent of urban contexts, although such theme has been a consequence, along with increased attention to environ- investigated mainly by considering active solutions (e.g. mental issues related to climate change (local production 13 The International Journal of Life Cycle Assessment and reduced transportation), the use of urban agriculture sited in the proximity of the production facility (in the Bar- (UA) has intensified, gradually beginning to be seen as a celona area, Spain). This type of UA waste has been selected viable alternative to rural agriculture not only from a purely based on the facts that tomatoes are a widespread crop and feeding (food-self-sufficiency) point of view (Tomlinson their plants wastes present several composting difficulties due 2011; Rufí-Salís et al. 2020; Sanyé-Mengual et al. 2015c), to their high salinity and lignin content (Dunlop et al. 2015; but also thanks to its attitude in reducing and mitigating the Llorach-Massana et al. 2017), so from a life-cycle perspec- negative impacts exerted on natural and urban areas (Zezza tive it is highly encouraged to find alternative uses for them and Tasciotti 2010) and its potentiality in providing relevant as a by-products. Specifically, the LCA methodology has social and economic benefits (Orsini et al. 2013; Specht et al. been applied to determine the carbon footprint and embodied 2013; Sanyé-Mengual et al. 2015a). On the other hand, the energy, in terms of carbon equivalent emissions ­(CO2 eq.), increased UA activity reflects in a growth of agricultural embedded as biogenic carbon within the envelope material waste production and that could represent a criticality in under study. Finally, the environmental impact of the new urban environments. Vegetal wastes, in fact, commonly have proposed envelope material has been compared to that of the three possible disposal scenarios, i.e. landfilling, composting most commonly used infill wall components on the market. and incineration, all of which do not allow crops to act as a carbon capture and storage system (Peri et al. 2022; Rizzo et al. 2023). Conversely, such disposal scenarios return the 2 Materials and methods sequestered carbon to the atmosphere in a brief period (less than 1–2 years) in terms of CO, ­CO2 or ­CH4 emissions (La As previously mentioned, the new innovative composite bio- Gennusa et al. 2016). Thus, these emissions can be consid- material is based on plant fibers derived from the pruning ered part of a fast carbon cycle. According to the current shoots of tomato plants. More specifically, this new material concern regarding climate change, there is great interest in is intended to be used as a building envelope (i.e. exterior preventing these fast carbon emissions. Producing new build- masonry) infill element as a sustainable alternative to the ing materials with valueless agricultural wastes, which can most common materials currently used for this purpose in be instead considered valuable feedstocks, would avoid the the climatic and construction context analyzed, namely hol- conventional disposal scenarios and create stable materi- low bricks, tuff blocks and light concrete blocks. als with long lifespans (20 years or more) that could store This section describes in detail the feedstocks used to ­CO2 emissions sequestered by crops, transforming them into produce the new infill wall (envelope) material, the produc- biogenic carbon. Therefore, UA could conceptually provide tion procedure of such material and the approaches utilized sustainable food to cities as well as low-carbon raw materials to perform the environmental assessment of the new material to produce new and sustainable by-products, resulting in the in order to also determine its carbon footprint and embod- reduction of the carbon footprint related to crops, buildings ied energy according to the Life Cycle Assessment (LCA) and by-products derived from UA waste (Sanyé-Mengual methodology, in reference to the analyzed context. The well- et al. 2015b). Hence, based on these assumptions and also known LCA approach has, indeed, proven to be an effective from a circular economy standpoint, a good way to manage instrument to support actions aimed at the environmental UA waste, and thus transform it from a criticality to a valu- improvement of the building sector (Allacker et al. 2019; able opportunity, is to reuse it as an alternative natural raw Mirzaie et al. 2020; Fnais et al. 2022). material for the production of innovative low-impact building Specifically, the main objectives of the environmen- envelope components in the vicinity of the place where they tal assessment of the new material are: (i) to determine the are intended to be used. According to such local scale pro- fixed biogenic carbon; (ii) to perform a LCA of the new UA duction scenario, indeed, the carbon emissions fixed by UA waste-based material; (iii) to compare the carbon footprint and waste-based envelope materials would likely be higher than embodied energy of the new UA waste-based material with the pollutant emissions generated during the production and those of other traditional infill wall components; (iv) to provide transportation stages of the materials. In addition, the deple- limits and recommendations for the production of more sustain- tion of other raw materials would be avoided. Nevertheless, able infill wall materials produced with tomato waste plants. to the best of our knowledge, a lack of an overall environmen- tal assessments of such local scale low-impact scenario has emerged (Sierra-Pérez et al. 2016a). 2.1 Feedstocks used to build the new In the aim of giving a contribution to cover this research envelope material gap, this work presents the environmental assessment of the manufacturing of an infill wall component (envelope mate- To build the new envelope material, tomato plant (Solanum rial) produced employing tomato plant stems (UA waste) to lycopersicum arawak variety) stems have been employed; be used in the construction and/or restoration of buildings such vegetal material came from a UA crop planted on the 13 The International Journal of Life Cycle Assessment Integrated Rooftop Greenhouse Laboratory (i-RTG-Lab) situ- (m2 year), which could be fixed by using such waste to pro- ated on the top of the ICTA-ICP building (Fig. 1) located in duce the new building envelope material, i.e. UA by-product, the Universitat Autònoma de Barcelona campus (Bellaterra, as proposed in this study. Spain), part of an experimental vertical farming installment Based on these considerations, two possible scenarios (Pons et al. 2015). Rooftop greenhouses are a reality that has can occur. On the one hand, if the sequestered emissions become increasingly popular in recent years, thanks to the ben- are higher than those relating to the production and trans- efits they provide for. portation of the new UA waste-based envelope material, it In this study, two samples elaborated with different propor- could be assumed that carbon emissions from production tions of tomato plant wastes and other materials (sand, water and transportation of the new material could be compensated and hydrated lime) have been proposed and analyzed. The by the biogenic carbon stored into tomato stems and leaves. sample properties and production properties will be described On the other hand, if the opposite circumstance occurs (i.e. in depth in Sect. 2.2.4. if the sequestered emissions are lower than those relating to the production and transportation phases of the new mate- 2.1.1 Carbon content of UA tomato plants waste rial), the carbon footprint of the new UA waste-based com- and carbon sequesterable by the new material ponent would still be lower compared to that attributable to traditional products since the depletion of other raw materi- The carbon (C) content of the tomato plant wastes used for the als would be avoided. study has been determined through elemental analysis using a ­LECO© analyzer (LECO 2021). Then, Eq. 1 was used to esti- mate the potential ­CO2 equivalent ­(CO2 eq.) emissions that the 2.2 Environmental assessment of the new material waste of the i-RTG could sequester ­(Csequestered) on annual basis. In this section the authors describe the approach used to DW prod. kgCO eq. Csequestered = ⋅ C% + O2eq. = 2 2 (1) assess the comprehensive environmental impact of the new Ai−RTG m ⋅ year building material. where DW prod. is the annual i-RTG dry waste production obtained by weighing the waste of tomato plants stems and 2.2.1 Goal and scope definition leaves at the end of a crop cycle, Ai−RTG is the i-RTG crop ­ 2, C% is the percentage of carbon content area equal to 84.3 m In order to fully and thoroughly assess the environmental in dry waste per unit of mass measured through elemental impact of the two samples (A and B) of the new material analysis of the plants stems and O2eq. is the equivalent mass three main aspects were investigated. Precisely, other than (kg) of oxygen from the ­CO2 emissions fixed as C within performing a classic Life Cycle Assessment (LCA), it was the dry waste. decided to also estimate the carbon footprint and the embod- Referring to the analyzed case, the i-RTG, with a crop ied energy indicators (that are based on the LCA method- area of 84.3 ­m2, produces 27.4 kg of dry waste tomato stem ology as well), for a dual scope as better explained in the annually, equivalent to 0.33 kg/(m2 year), while the C con- following. Specifically, the carbon footprint and embodied tent in waste stems correspond to 35.7% of the total dry energy indicators were chosen mainly for the purpose of mass. Consequently, according to Eq. 1, the i-RTG-Lab making a comparison between the new material and some tomato crop has the potential to sequester 0.42 kg ­CO2 eq/ other conventional (non-natural-based) most commonly Fig. 1  ICT-ICP building (left), inside of the i-RTG-Lab (middle) and experimental tomato crop (right) 13 The International Journal of Life Cycle Assessment used infill wall materials on the market (i.e. hollow bricks, in the field of building construction (Batista dos Santos et al. tuff blocks and light concrete blocks) in a rapid manner and 2022a, b; Shi et al. 2022; Goh et al. 2022). based on two valid and recognized indicators. While, the LCA was applied to the two samples (A and B) of the new 2.2.2 Functional unit material to compare them with each other more thoroughly also in reference to other possible critical environmental Similar to previous LCA studies concerning other building issues not directly highlighted by the carbon footprint and materials (Pargana et al. 2014; Sierra-Pérez et al. 2016a), embodied energy indicators. and considering that the new proposed material should The carbon footprint (­ kgCO2 eq.) is defined as “a meas- ensure thermal insulation characteristics similar to other ure of the total amount of carbon dioxide ­(CO2) and meth- traditional infill wall components, the selected functional ane ­(CH4) emissions of a defined population, system or unit (FU) for the performed assessment has been defined as activity, considering all relevant sources, sinks and storage the mass (kg) of material required to provide a fixed ther- within the spatial and temporal boundary of the population, mal resistance R ­(m2 K/W) for a given surface A ­(m2), as system or activity of interest…and it is calculated in terms reported in Eq. 2. of carbon dioxide equivalent (­ CO2 eq.) emissions” (IPCC 2014). To proceed with the carbon footprint calculation, the FU = R𝜆𝜌A (2) GHG protocol calculation method (ISO 2018) was applied where 𝜆 is the thermal conductivity (W/m K) and 𝜌 is the to determine fossil ­CO2, biogenic ­CO2 and ­CO2 uptake. density (kg/m3) of the analyzed samples. For the purpose of While, the embodied energy—EE (MJ) is given by the ­ 2 K/W and 1 m this work it was decided to set values of 1 m ­ 2 sum of all of the energy required to produce any goods or for R and A, respectively. services, considered as if that energy was incorporated in the product itself (Goedkoop et al. 2009). 2.2.3 Production process description and system As for the LCA (ISO 2021), according to the Environmen- boundaries tal Product Declaration (EPD) for construction products (CEN 2021), the following impact categories have been considered: Figure 2 describes the stages (raw materials, transportation and production) involved in the creation of the proposed infill wall • Climate change—GWP, not including biogenic carbon material. This process is similar to that used by S. Benfratello (kg ­CO2 eq.); et al. (2013) to produce a hemp-lime bio-composite insulation • Ozone depletion—ODP (kg CFC 11 eq.); material. At the end of the tomato cropping period, plants are • Acidification—AP (kg ­SO2 eq.); manually collected and placed next to the greenhouse where • Eutrophication aquatic freshwater—EP-freshwater (kg P eq.); they are naturally dried. Once the plants are dry, their stems • Eutrophication aquatic marine—EP-marine (kg N eq.); can be easily separated from the leaves. Then, dry wastes are • Photochemical ozone formation—POCP (kg NMVOC eq.); transported to the production plant where they are chopped to • Water use—WDP ­(m3); obtain fibers of 4 mm in length and later mixed with water, • Depletion of abiotic resources—minerals and metals— sand and hydrated lime. The resulting mixture is placed in a ADP-minerals&metals (kg Sb eq.); mold for 5 days, after which the mix is demolded and naturally • Depletion of abiotic resources—fossil fuels—ADP-fossil dried. Once the mixture is dry, the infill wall material is ready (kg oil eq.); for transportation to the installation point. As Fig. 2 shows, the system boundaries include the UA To carry out the above analyses, i.e. EE estimation and waste raw material obtained (dry tomato plant stems), the LCA application, the Recipe midpoint (H) was selected transportation of such material to the production plant and as calculation method (Goedkoop et al. 2009; ReCiPe the production of the infill wall component. The transpor- 2016; Huijbregts et al. 2017; Lamnatou et al. 2018); whilst tation of the finished product to the utilization point is not ­SimaPro© software (https://​simap​ro.​com) in combination included in the system boundaries as it is not a mandatory with the Ecoinvent database (https://e​ coinv​ ent.o​ rg) was used requirement according to the EPD for construction products as applicative tool. (CEN 2021). Moreover, since the object of this analysis is The choice to use the ReCiPe method stems from the fact associated to the new material using the wastes produced by that, although there might be more up-to-date (and more an already existent UA crop, the tomato production phase complicated) procedures, this still represents an effective has not been included in the system boundaries as well. and currently recognized (considered useful) method to con- Nevertheless, it should be considered that the environmental vert life cycle inventories to a limited number of life cycle impacts of tomato production may be also reduced because impact scores, as evidenced by recent studies that refer to it stem waste management would be avoided. 13 The International Journal of Life Cycle Assessment Fig. 2  Production process of the new envelope material and system boundaries selected for the LCA 2.2.4 Inventory assessment and assumptions described in Fig. 2 and based on the proportions of a previ- ous study on a hemp-lime bio-composite building material Two samples, A and B, have been produced (Fig. 3) and (Benfratello et al. 2013). For each sample different materials analyzed in this study according to the production process proportions were used (Table 1), in order to obtain samples 13 The International Journal of Life Cycle Assessment Fig. 3  Tomato plant stems (left) used for the production (middle) of the new infill wall material (right) characterized by different properties and densities and, con- needed by the equipment used (kW) and the operation time sequently, the total mass to achieve the FU varied for each of (h) required to produce one unit of mass (kg) of infill wall them. That is, for the same fixed value of thermal resistance material, referring to the Spanish energy mix (RED). These (as reported in Sect. 2.2.2), in sample A it was decided to data were registered and collected for each analyzed sample, enhance mechanical characteristics, while in sample B it was resulting in an energy consumption for kg of stems equal decided to enhance thermal characteristics. Therefore, FU to 0.984 kWh and 0.165 kWh for chopping and molding of sample A is characterized by larger thickness and heavier processes, respectively. weight than FU of sample B. To do this, the composition of the two samples was made to vary as shown in Table 1. 2.2.5 Carbon removal from the atmosphere Nevertheless, it should be stressed again that, since the new bio-composite material is intended to be used as a sustainable As previously reported, to proceed with the carbon foot- alternative to other most commonly used building envelope print calculation, the GHG protocol calculation method (ISO infill components (i.e. hollow bricks, tuff blocks and light 2018) was applied to determine fossil ­CO2, biogenic ­CO2 concrete blocks), both samples are able to meet the minimum and ­CO2 uptake. In particular, to simplify the calculation characteristics required for such a type of building element. of the amount of C ­ O2 that is removed from the atmosphere Regarding the production plant, it has been assumed that it when producing the new infill wall material, the following could be sited either in northern or southern Barcelona, where breakdown was adopted (Eq. 3). different industrial areas can be found; hence, assuming an Cremoval = Crawmaterials + Ctransportation + Cproduction − Csequestered average distance of 25 km between i-RTG-Lab and the pro- (3) duction plant. As for the transport means, Euro 6 lorries with a load capacity of between 3.5 and 7.5 tons have been considered. where Craw materials , Ctransportation and Cproduction represent Lime and sand could be provided from a local quarry located the ­CO2 emissions related to raw materials, transportation in Garraf, 35 km far from Barcelona, by means of Euro 6 lor- and production, respectively and have been extracted from ries, as well, with a load capacity of between 7.5 and 16 tons. ­SimaPro© software (https://​simap​ro.​com) by using the Rec- Euro 6 trucks were considered because these represent ipe method (ReCiPe 2016); while, Csequestered is the amount the most prevalent heavy goods vehicles HGVs in the area, of ­CO2 sequestered by tomato plants, estimated as previously and it is assumed that they will not be replaced in the near described in Sect. 2.1.1. In this study, it was assumed that future (TLT 2016). carbon captured by plant remains stored in the new material, The energy required to chop the fibers and to perform as is the case with other bio-composite lime-based materi- the molding process was estimated considering the power als such as concrete made with hemp (Ip and Miller 2012). Table 1  Sample properties for the selected FU 3 Results and discussion Parameter Unit Sample A B In this section the results of the performed analyses will be reported and commented. Composition Stem fiber content % 20% 30% Lime content % 32% 28% Sand content (carbonate % 32% 28% 3.1 Environmental assessment of the new material calcium) and comparison between samples Water content % 16% 14% Properties Weight to produce the FU kg 75.7 42.8 Concerning the LCA, Table 2 shows a comparison between Density kg/m3 733.7 658.3 the outcomes of the analysis application to the two samples Thermal conductivity W/(m K) 0.103 0.065 A and B for the considered impact categories. 13 The International Journal of Life Cycle Assessment Table 2  Comparison between sample A and sample B impact categories of LCA and impact reduction of sample B with respect to sample A Impact category Unit Sample Deviation of B from A B A Climate change—GWP, not including biogenic carbon kg ­CO2 eq 9.9E + 00 7.48E + 00 − 24% Ozone depletion—ODP kg CFC 11 eq 1.4E − 06 1.09E − 06 − 22% Acidification—AP kg ­SO2 eq 5.3E − 02 3.99E − 02 − 25% Eutrophication aquatic freshwater—EP-freshwater kg P eq 1.8E − 03 1.33E − 03 − 26% Eutrophication aquatic marine—EP-marine kg N eq 2.9E − 02 2.25E − 02 − 22% Photochemical ozone formation—POCP kg NMVOC eq 3.2E − 02 2.36E − 02 − 26% Water use—WDP m3 8.3E − 02 4.75E − 02 − 43% Depletion of abiotic resources-minerals and metals— kg Sb eq 2.7E − 01 1.95E − 01 − 28% ADP-minerals&metals Depletion of abiotic resources-fossil fuels—ADP-fossil kg oil eq 3.0E + 00 2.29E + 00 − 24% As it can be noticed sample A is characterized by a higher to this, the impact category with the largest difference (43% environmental impact for all the considered categories. Spe- higher) is WD, which could, in fact, be explained by the fact cifically, on average sample A environmental impact is 26.3% that sample B uses 40% less water than sample A for all pro- higher than sample B. This can be ascribed to the fact that duction stages. It should be also pointed out that, although a sample B has lower values of density and thermal conductivity higher stem content within the material may be recommended, most probably linked to the higher percentage of tomato stems this could worsen the mechanical properties of the material. compared to sample A; therefore, less raw materials (hydrated Figure 4 shows sample A and sample B environmen- lime, sand and water) are required to produce a FU. Connected tal impacts distributions for each of life cycle phase, i.e. Fig. 4  Sample A and Sam- ple B environmental impact distribution per life cycle stages (Climate change—GWP, not including biogenic carbon; ozone depletion—ODP; acidification—AP; eutrophica- tion aquatic freshwater—EP- freshwater; eutrophication aquatic marine—EP-marine; photochemical ozone formation —POCP; water use—WDP; depletion of abiotic resources- minerals and metals—ADP- minerals&metals; depletion of abiotic resources-fossil fuels—ADP-fossil; embodied energy—EE) 13 The International Journal of Life Cycle Assessment production, transportation and raw materials. In this case, As for the carbon footprint, the results for the two ana- from the comparison of the two samples, no significant dif- lyzed samples are reported in Table 3. ference seems to occur. As it could have been expected, sample B is the one char- As it can be observed, production is the main contribu- acterized by lower carbon footprint not including biogenic tor to all of the impact categories except for WD, where the carbon. In fact, sample B, other than being characterized by a main contributor is raw materials, due the water required to better thermal conductivity, is also the one requiring less mate- produce the sample and to extract sand. From the performed rial to produce a FU and causing lower environmental impacts. analysis, it also resulted that the stem chopping process is In Table 3 net carbon footprint refers to the difference responsible for a share of almost 90% of the production between the emissions generated during the raw materials, stage impact. It should be considered that the environmen- transportation and production stages minus the C emissions tal impacts in the present study were calculated in reference fixed by the tomato stems used to produce the samples. As to the manufacturing of samples at the laboratory scale. An it can be seen, for both samples the net carbon footprint industrialization of the process could reduce most of the is negative, meaning that the biogenic carbon fixed within environmental impacts associated to the production stage, the material is higher than the emissions resulting from the although transportation-related impacts could increase. production of the same material, from a life cycle perspec- Regarding the raw materials stage, this is responsible for tive. On average, fixed biogenic carbon reduces the carbon less than 20% of the environmental impacts for all the cat- footprint by 212%. Such carbon fixed within the infill wall egories, except for WD. In this case the largest impacts are materials will finally come back to the atmosphere at the caused by the supply of lime and sand needed to produce end-of-life of the material; however, the speed of the carbon the samples, which are responsible of about 44% and 55% cycles, in comparison with conventional waste management of the total environmental impact of raw materials stage, solutions (i.e. incineration and/or composting), has been sig- respectively. In particular, the impact associated to lime is nificantly reduced. It should also be reminded that emissions probably caused by the calcination of stones extracted from from end-of-life are not accounted as they are out of the mines at 1000 °C, while the impact related to sand could be defined system boundaries. ascribed to its grinding necessary to obtain sand powder. Water contributes to just 0.4% on the impact. 3.2 Comparison with other infill wall materials As for the transportation of raw materials to the produc- of the building envelope tion plant, this has a lowest environmental impact on all categories, i.e. less than 1%. The use of local materials To elaborate further on the analysis, it was then decided seems to notably reduce the environmental impacts from to compare the new material with some other conventional the transportation phase in comparison with other studies (non-natural-based) most commonly used infill wall com- for which this stage represents more than the 30% of the ponents on the market, i.e. hollow bricks, tuff blocks and carbon footprint and embodied energy (Sierra-Pérez et al. light concrete blocks. 2016a). This confirms the appropriateness of the proposed From the data reported in Table 4 it can be seen how both strategy, i.e. using urban (rather than rural) agricultural sample A and sample B present lower values of the thermal wastes for innovative building envelope materials in the conductivity and density in comparison to the other conven- near area where they are to be used. tional materials, indicating that an elevated mass is required Regarding the Embodied Energy (EE) indicator the to produce a FU; consequently, the building structure might obtained results (which are also included in the following need to be reinforced for the installation of the new material, f Fig. 4) are equal to 2.0E + 02 MJ and 1.55E + 02 MJ for which would increase the overall environmental impact of sample A and sample B, respectively, with an impact reduc- the building. tion of sample B with respect to sample A of − 22%. Table 3  Carbon footprint of the analyzed samples according to the defined FU Raw materials, transportation and production Tomato plant waste Ratio ­CO2 in waste/ Net carbon footprint* biogenic carbon content emitted for Fossil Biogenic CO2 Total transformation CO2 eq CO2 eq uptake kgCO2 eq kgCO2 eq kgCO2 eq kgCO2 eq kgCO2 eq % kgCO2 eq Sample A 9.9 0.2 0.2 9.9 19.8 2.0 − 9.9 Sample B 7.5 0.2 − 0.2 7.5 16.8 2.7 − 9.3 * Emissions from raw materials, transportation and production stages minus C emissions fixed within the tomato stems 13 The International Journal of Life Cycle Assessment Table 4  Comparison between Thermal Density FU Life cycle perspective sample A, sample B and other conductivity (weight) commonly used infill wall Carbon Embodied materials (Hammond and Jones footprint energy 2006; Hammond and Jones 2008; UNI 2014) W/(K m) kg/m3 kg kgCO2 eq MJ Tomato stem (Sample A)* 0.103 733.7 75.7 9.9 202.9 Tomato stem (Sample A)** 0.103 733.7 75.7 − 9.9 202.9 Tomato stem (Sample B)* 0.065 658.3 42.8 7.5 155.5 Tomato stem (Sample B)** 0.065 658.3 42.8 − 9.3 155.5 Hollow bricks 0.337 1000 337.1 74.2 1011.2 Tuff blocks 0.550 1600 880 15 264 Light concrete blocks 0.500 1400 700 231 2450 * Not including biogenic carbon ** Including biogenic carbon Anyway, despite such possible limitation (that should dividing the mass of infill wall material needed to produce be further explored in order to be verified), based on the the FU (Table 1) by the above mentioned potential annual obtained carbon footprint and embodied energy values, the production. These results show that about half of the annual new material seems to be characterized by a better environ- wastes produced by the i-RTG-Lab surface (total area of mental performance from a life cycle perspective compared 84.3 ­m2) are required to produce 1 ­m2 of material. to the other materials. This is probably due to the fact that Approximately 215 m ­ 2 or 253 m ­ 2 of infill wall surface the lower impacts associated to the raw materials transpor- area could be produced per hectare of a crop for sample A tation may compensate for the higher impact related to the or sample B, respectively. Meaning that, for example, the amount of raw materials required to produce a FU. infill wall material needed for the for external envelope of It must also be underlined that a difference can be observed a 4-floor building (20 m wide, 20 m long and 15 m high) depending on whether the biogenic carbon is considered or with an external surface of 1600 m ­ 2 (without discount- not. In fact, if biogenic carbon is taken into account, despite ing empty surfaces for windows) would require an annual embodied energy value remaining unchanged, the actual waste production of 7.5 hectares or 6.3 hectares of tomato environmental impact in terms of ­CO2 eq. emissions would crop for sample A or sample B, respectively. Therefore, the be lower. Therefore, if biogenic carbon is included when dimensions of UA may limit the production of infill wall computing the ­CO2 emissions, embodied energy should not materials, such as those proposed in the present research. be used as the main indicator for decision-making purposes Consequently, it may be necessary to retrieve waste stems when selecting more environmentally friendly materials. from non-UA crops, going from peri-urban to rural contexts. Such circumstance, however, as previously mentioned would 3.3 Potential production of the new material cause an increase of the transportation distances, hence, of the environmental impact of the new material. Aside from the amount of carbon sequesterable by the new material, it is also important to determine the quantity of infill wall material that could be manufactured per area of 4 Conclusions crop. In fact, this information could be essential to estimate if in the future UA could supply enough waste to produce The present work started from considerations regarding a the infill wall materials that a city may demand for new and/ possible and innovative solution to contribute to the decar- or to be restored buildings. bonization of urban environments. In fact, so far in order to The potential annual production of the i-RTG-Lab tackle climate change the attention of researchers has been resulted being 1.6 and 1.1 kg/m2 year of infill wall mate- mainly paid to the attempt of limiting the energy consump- rial for samples A and sample B, respectively. The higher tion (and pollutant emissions) of buildings guaranteeing value obtained for sample A is ascribable to the fact that the the required performances to the outdoor and indoor air; tomato fiber content in this case is lower (20%, see Table 1) while, more recently the threats related to the pandemic and than that of sample B (30%, see Table 1). Consequently, the energy-economic crises have called for a more conscious crop surface required to produce a FU (i.e. for 1 m­ 2 of infill design of strategies/solutions, aimed at a more sustainable 2 2 wall material) is equal to 46.6 m­ and 39.5 m­ for samples A and self-sufficient urban metabolism. Therefore, although and B, respectively. These values were, indeed, calculated by the energy, environmental and health concerns remain on the 13 The International Journal of Life Cycle Assessment table, the issues related to the economic and safety aspects, (e.g. new job opportunities), other than contributing to the in terms of self-support based on local resources, must now- strengthening of national security (reduced dependency on adays even more properly be addressed. In light of this, the foreign supplies). main objective of the work has been that of assessing the Acknowledgements This work was carried out within the Spanish environmental impact, from a life cycle carbon neutrality research project “Agro-urban sustainability through rooftop green- perspective, of an innovative building envelope component houses. Eco-innovation on residual flows of energy, water and ­CO2 derived from local UA wastes to be used in the proximity for food production” (MINECO: CTM2013-17-47067-C2-1-R) and the of the production site. The innovative aspect lies in the pos- research project “SUSTAIN/ABLE—SimultaneoUs STructural And energetIc reNovAtion of BuiLdings through innovativE solutions” sibility of addressing two problems simultaneously through (20174RTL7W_003). a single solution, i.e. reduce urban wastes and use locally produced and more sustainable building materials. Author contribution All authors contributed to the study conceptual- The results of the assessment performed on the new ization, methodology, formal analysis and investigation, visualization and writing (original draft, review and editing). All authors read and proposed UA waste-based material put in evidence the sig- approved the final manuscript. nificant potential of such a type of infill wall component in fixing carbon emissions from UA crops, allowing to also Funding Open access funding provided by Università degli Studi di compensate those relating to the production and transporta- Palermo within the CRUI-CARE Agreement. The PRIN (Programmi di Ricerca Scientifica di Rilevante Interesse Nazionale) of the Italian tion stages of the new material life cycle. In particular, the Ministry of Education, University and Research. higher the employed percentage of tomato plant stem is the lower the carbon footprint is, due to the biogenic carbon Data availability Data sharing not applicable to this article as no data- content. On the other hand, given the high density of the sets were generated or analyzed during the current study. new infill wall component, an equally high amount of waste material is required for the production of the component. Declarations Therefore, different urban crops with higher waste produc- Conflict of interest The authors declare no competing interests. tion rates (e.g. pepper) are actually under consideration for further possible study. Open Access This article is licensed under a Creative Commons Attri- bution 4.0 International License, which permits use, sharing, adapta- Of course, it should be here underlined that this is a first tion, distribution and reproduction in any medium or format, as long investigation on this subject on which improvements can be as you give appropriate credit to the original author(s) and the source, made as a future research development. In fact, this study is provide a link to the Creative Commons licence, and indicate if changes meant as a preliminary analysis of the new bio-composite were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated material as an innovative and sustainable solution to employ otherwise in a credit line to the material. If material is not included in an already existent waste (produced by a greenhouse rooftop the article's Creative Commons licence and your intended use is not UA crop used for feeding purposes) that would result in an permitted by statutory regulation or exceeds the permitted use, you will avoided impact relating, instead, to the supply and use of need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://​creat​iveco​mmons.​org/​licen​ses/​by/4.​0/. new raw materials. Anyway, the avoided impact deriving from new raw materials is certainly an interesting issue that deserves attention and that should thus be properly investi- gated in a future study. 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Int J Life Cycle Assess. https://​doi.​org/​10.​1007/​ s11367-​014-​0836-9 13 The International Journal of Life Cycle Assessment Authors and Affiliations Pere Llorach‑Massana1,2 · Laura Cirrincione3 · Jorge Sierra‑Perez4,5 · Gianluca Scaccianoce3 · Maria La Gennusa3 · Javier Peña2 · Joan Rieradevall1,6 1 4 Sostenipra Research Group (2017SGR 1683), Institute Department of Design and Manufacturing Engineering, of Environmental Sciences and Technology (ICTA), Z EINA, University of Zaragoza, María de Luna 3, Building, Universitat Autònoma de Barcelona (UAB), 50018 Saragossa, Spain Campus UAB, 08193 Bellaterra, Barcelona, Spain 5 Water and Environmental Health‑IUCA Research Group, 2 Elisava Research Group, Barcelona University School University of Zaragoza, 50018 Saragossa, Spain of Design and Engineering UVIC-UCC​, La Rambla 30‑32, 6 Department of Chemical, Biological and Environmental 08002 Barcelona, Spain Engineering, School of Engineering, Universitat 3 Department of Engineering, University of Palermo, Viale Autònoma de Barcelona (UAB), Building Q, Delle Scienze Bld. 9, 90128 Palermo, Italy 08193 Bellaterra, Barcelona, Spain 13