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Article

Life Cycle Assessment of Fungal-Based Composite Bricks

by
Lisa Stelzer
1,
Friederike Hoberg
1,*,
Vanessa Bach
2,*,
Bertram Schmidt
1,
Sven Pfeiffer
3,
Vera Meyer
1 and
Matthias Finkbeiner
2
1
Applied & Molecular Microbiology, Institute of Biotechnology, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany
2
Sustainable Engineering, Institute of Environmental Technology, Technische Universität Berlin, 10623 Berlin, Germany
3
Department of Digital Design Planning and Building, Hochschule Bochum, Am Hochschulcampus 1, 44801 Bochum, Germany
*
Authors to whom correspondence should be addressed.
Sustainability 2021, 13(21), 11573; https://doi.org/10.3390/su132111573
Submission received: 8 September 2021 / Revised: 7 October 2021 / Accepted: 15 October 2021 / Published: 20 October 2021
(This article belongs to the Section Green Building)
Browse Figures
Review Reports Versions Notes

Abstract

:
Fungal-based composites as substitutes for construction materials might represent a promising solution to reduce the environmental burdens of the building industry. Such composites can be produced biotechnologically through the cultivation of multicellular fungi that form dense mycelia whilst growing into and onto residual plant biomass from agriculture and forestry. As comprehensive environmental assessments are missing, this paper conducts a life cycle assessment for fungal-based composite bricks considering the categories of climate change, eutrophication, acidification, smog, water scarcity, and land use. Electricity for sterilization, incubation, and the drying process led to 81.4% of a total 0.494 total kg CO2 eq. for climate change and 58.7% of a total 9.39 × 10−4 kg SO2 eq. for acidification. Further, hemp shives and grain mix were identified as hotspots for eutrophication (77.7% of 6.02 × 10−4 kg PO4−3 eq.) and land use (81.8% of 19.4 kg Pt eq.). However, the use of hemp shives, rapeseed straw, or poplar wood chips did not differ in the environmental impacts. Further, lab-scale production was compared with industrial scale-up, which is mostly characterized by energy efficiency showing reduced impacts for all considered categories, e.g., a decrease of 68% in climate change. Recycling should be included in future studies as well as considering the use and end-of-life phase.

1. Introduction

Fungi have been used by mankind in numerous ways since prehistoric times. Commonly known is their use as food or in food fermentation. Less well-known is that fungi have also long played a role as a source of materials and medicine.
The Iceman mummy found at Tisenjoch, also known as “Ötzi”, carried parts of tinder fungus Fomes fomentarius and birch polypore Piptoporus betulina. These fungi were probably used for fire-making and healing purposes [1]. In particular, the tinder fungus was used for thousands of years to obtain tinder. This soft felt-like material served as a spark catcher for fire making. In addition, it was suitable for making textile items. The formerly widespread traditional use of this “felt leather” is kept alive today in some regions, primarily in Eastern Europe, or through innovative product designers, e.g., ZVNDER [2], MYLO [3], or NEFFA [4].
In biotechnology, unicellular and filamentous fungi play a prominent role due to their metabolic versatility and robustness and are therefore harnessed by different industries including pharma, chemical, food, feed, biofuel, and textile industries to produce drugs, platform chemicals, enzymes, food additives, and organic acids [5]. Most recently, filamentous fungi, i.e., mycelium-forming fungi have gained much interest because their biomass consists of a dense three-dimensional cellular network with notable material properties [6]. Whilst growing onto and into lignocellulosic plant residual materials derived from agriculture and forestry, the mycelia form a solid composite material [5]. Such composite materials can be used for packaging (Ecovative [7]) or interior design (Mogu [8]). Others explore the use of the pure fungal mycelium as a leather alternative (MycoWorks [9], Mylea-Mycotech [10]) or fabric (NEFFA [4]).
So far, research on fungal-based composites as an alternative construction material has only taken place on a laboratory or pilot-plant scale. The first artistic but experimental buildings have been constructed, e.g., the 13 m high ‘Hy-Fi’ installation in front of the MoMA [11] and the ‘Monolito Micelio’ Pavilion [12]. In a future scenario, customers could select and customize building elements before they become cultivated and could, e.g., use them as partition walls in a previously continuous space. Such options would give residents flexibility in the design and during the construction phases and would allow custom-made buildings.
This study focuses on the potential use of fungal composites as a building material to address amongst others the environmental problem of climate change to which the building sector is contributing about 23% of total CO2 emissions globally [13]. Furthermore, it needs to be considered that the building sector is constantly growing [14], most likely leading to an increase in CO2 emissions as well as water and fossil resource consumption [15].
While the use of renewable materials is widespread in other sectors such as the consumer industry, the construction sector is characterized in many areas by traditional materials and production methods. The utilization of fungal-based bricks consisting of by-products from agriculture or forestry could offer a alternative to reduce the environmental burden of the building industry. The replacement of conventional materials, such as concrete or lime sandstone, with these biologically produced and thus biodegradable materials could considerably contribute to reaching the UN sustainability goals [5].
Studies on environmental impacts including life cycle assessments (LCA) have not been carried out yet with respect to fungal-based composite, despite numerous studies addressing their physico-mechanical properties [16,17]. Therefore, the aim of the current study is to determine the potential environmental impacts regarding the cultivation of Fomes fomentarius on hemp shives, rapeseed straw, and poplar wood chips as a standardized brick according to the DIN EN 771-1 [18], thus also enabling a comparison with common materials.

2. Materials and Methods

A LCA based on ISO 14040/44 was carried out [19,20]. In this section, the goal and scope definition (Section 2.1) and inventory analysis (Section 2.2) are presented.

2.1. Goal and Scope Definition

The goal of this case study is to identify the potential environmental impacts of fungal-based building materials on a lab scale. The function of the fungal-based composite brick is providing stability and thermal regulation for buildings. Thus, the functional (declared) unit of one fungal-based brick standardized to the German ‘Normalformat’ (NF) brick (24 × 11.5 × 7.1 cm) [18] made out of hemp shives is chosen (see Figure 1). The intended application of this LCA is to determine the potential environmental hotspots of the lab-scale production of fungal-based bricks. The hemp shive composite brick is also compared to bricks that are based on the alternative plant substrates rapeseed straw and poplar wood chips. Within the discussion in Section 4.3, the fungal-based composite bricks are further compared with conventionally used bricks in construction to estimate possible reduction potentials.
A “cradle-to-gate” study is carried out to cover the production process, setting the system boundaries to include all unit processes from cradle to gate, as shown in Figure 2. The use phase and the end-of-life phase are not considered.
In the following, the studied product system is defined in detail. The included processes are shown in the flow diagram in Figure 2. The data of this foreground system were selected on site (laboratory) via measurements of, e.g., the electricity of equipment. Missing data were determined via literature research and by use of databases. The used equipment was not included in the modeling. Further, a cut-off of 5% was defined. Applied data and corresponding modeling assumptions including allocation procedures are explained in Section 2.2.
The production of the fungal-based brick from the fungal mycelium of tinder sponge Fomes fomentarius (strain: GaG41) and solid particulate plant material was carried out in a microbiological laboratory (“lab scale”). The brick was produced within a cultivation system conducted in four steps (see Figure 2). In every step, the cultivation conditions were changed to gradually increase the fungal biomass.
For Step 1, pre-culture, the mycelium of tinder sponge Fomes fomentarius (strain: GaG41) was cultivated in a petri dish containing a nutrient-rich agar medium (complete medium). For this, a small amount of mycelium was transferred (inoculated) onto the agar plate and incubated for approximately seven days until the mycelium colonized the agar plate. Experiments have shown that direct inoculation of larger quantities of solid substrates (hemp shives, rapeseed straw, or poplar wood chips) from agar plates lead to poor, uneven growth [21]. Therefore, as an intermediate step, the fungus was cultivated in grain cultures producing mycelium brood.
In Step 2, grain culture, mycelia were scraped off and used to inoculate a rye grain culture, which induced the secreted enzyme reservoir of F. fomentarius to degrade cellulosic components within seven days of cultivation. For this step, rye was autoclaved with water and a small amount of gypsum, which helped to keep the single grains intact.
Step 3, substrate culture, encompassed the transfer of the rye grain inoculum onto different lignocellulosic plant substrates including hemp shives (or rapeseed straw or poplar wood chips) in cultivation bags and further cultivation for 12 days. Growth was supported by adding water and wheat flour to induce enzyme secretion. During incubation, the substrate culture was mixed after seven days.
Step 4, molding, involved transfer of the mycelium-covered lignocellulosic plant substrate into brick molds to allow for a final 7-day cultivation phase that solidified the composite further. The molds were constructed according to EN 771 [18] measurements of a German ‘Normalformat’ (NF) brick, following the octametric system, out of coated plywood (28 mm screen printing plates). The plates were cut to size with a handsaw and joined with screws. To vary the surface of individual bricks, these molds were equipped with inlays, 3D-printed from polylactic acid. Eventually, the mold was removed, and the mycelial growth in the composite material was inactivated through a 70 °C pasteurization step in a drying oven.
All cultivation steps were conducted at 24 °C, constant humidity, and constant light. Since the substrates used could also have been metabolized by many other organisms (e.g., bacteria, yeasts, and molds), sterile conditions were necessary to prevent the growth of these contaminants, which otherwise may have compromised the quality of the mycelium composites. Therefore, all media and tools that were in contact with growing mycelium cultures needed to be sterilized by using an autoclave. Besides the used substrates, the conditions for incubation during fungal growth determine the growth rate, total fungal biomass, and thus the strength of the composites produced. Therefore, temperature, exposure to light, and oxygen supply had to be controlled and kept constant to obtain stable product quality.
Potential environmental impacts were determined for the categories of climate change, acidification, eutrophication, smog (photochemical ozone creation) land use, and water scarcity, (see Table 1). The methodology of the Institute for Environmental Sciences in Leiden (CML) [22,23] in its version from 2016 was applied for climate change, acidification, and eutrophication, as it is one of the LCIA methods frequently used throughout Europe for years [24,25]. For the categories of land use, water scarcity, and smog, the recommendations of the Product Environmental Footprint [26] were followed, applying the LANCA method [27,28,29] as an aggregated single-score indicator for land use, the AWARE (Available Water Remaining) method [30] for water scarcity, and ReCiPe [31,32] for smog. No normalization and weighting methods were applied.

2.2. Inventory Analysis

The primary data for the production of fungal-based bricks were collected during lab cultivation; the secondary datasets were taken from the databases of Sphera (with SP 40) [33] and Ecoinvent 3.5 [34] (see Table 2) using the GaBi software [34] for modeling.
The following materials were modeled for Step 1: petri dishes (polystyrene), gloves (nitrile), and medium. Since no process for the petri dish was available in the databases, it was modeled based on general-purpose polystyrene, assuming thermal energy and electricity use, similar to comparable plastic polymer processing methods. The used nutrient medium contains defined amounts (see Table 2) of the following ingredients: malt extract, peptone from gelatin, glycerin, dextrin, agar, and deionized water. Since some data sets for these ingredients of the medium were not available, proxies were used based on similar properties. For malt extract, the proxy barley was used, since malt extract is mostly obtained from barley. As the production of malt extract out of malt and malt out of barley leads to a weight loss of approximately 22% according to Kunze [35], the input mass was adapted accordingly. Gelatin was used as a proxy for peptone since peptone is extracted from gelatin. Instead of dextrin, the dataset of starch was applied, as dextrin is a by-product of the starch production and is formed by the enzymatic degradation of starch. An alternative for agar is gelatin because it was formerly used to harden the medium.
In Step 2, the grain mix was modeled. It includes rye grains, gypsum, and deionized water. It was assumed that rye grains originate from Brandenburg. Accordingly a transport process of 50 km was estimated.
The substrate culture process (Step 3) used next to the substrates (hemp shives, rapeseed straw, or poplar wood chips) also substrate bags (made from polypropylene), deionized water for the hydration, and wheat flour. Hemp is produced in Brandenburg, for which it is assumed to be 50 km outside of the production facility in Berlin. For rapeseed straw and poplar wood chips, it was assumed that the products originate from Brandenburg as well, and the same transport distances were applied. Further, an economic allocation for rapeseed straw was applied as, compared to the other substrates, there was no suitable data set. The Sphera database [36] only contains one data set for rapeseed, which, however, requires the same agricultural cultivation process as the corresponding straw. Economically, rapeseed is three times more valuable than rapeseed straw [37,38]. Consequently, a sub process was created to allocate associated environmental impacts to rapeseed straw. A data set of wood chips was utilized for poplar wood chips.
Within Step 4 (molding), the electricity consumption for drying (drying oven) and the foil (polyethylene), which covers the brick mold, was included. It was assumed that the brick mold itself from coated plywood is used for over 100 bricks and only contributes to a very small share of the environmental impacts of one brick. Therefore, it was considered as negligible and is not considered in the model.
Additionally, in Steps 1–3, sterilization (autoclave) and, in Step 1–4, incubation (incubation room) of the materials were performed. The electricity consumption for the used autoclave and incubation room was modeled in each process separately. The energy consumption of the autoclave and the drying oven could be measured with a heavy current meter. The energy consumption for the incubation room was determined based on the calculated heating capacity (0.39 kW) for one hour of a standardized incubation room (30.6 m3) according to Formula (1), the area used therein (0.025%/per substrate bag), and a use of eight hours per day.
Q = V ∗ U – v a l u e ∗ Δ T = 30.6   m 3 ∗ 2.2 W m 3 ∗ K ∗ 5   K = 0.39   k W
Q = heat [W]
U-value = thermal transmittance [W/m3 ∗ K]
V = volume [m3]
∆T = temperature difference [K]
The produced waste was also included. The forming of polystyrene petri dishes results in a loss of approximately 20% polystyrene, as observed in practice, which is modeled as being incinerated, including credits for energy and steam. The remaining materials for pre-culture were disposed of with the commercial waste after usage. The polypropylene bags used in the substrate culture were assigned to the polypropylene incineration process as well. Furthermore, all used materials to be discarded were sterilized (autoclave) one more time before disposal to avoid carrying living organisms into the environment.
The associated amounts for one brick are provided in Table 2. and were measured and weighted on location (primary data).

3. Results

In the following, results are first shown for the hemp shive composite brick. A comparison of the different plant substrates is presented later on.
As shown in Figure 3 and Table 3, production step 3, substrate culture, has the highest impacts for all considered categories (for climate change, the molding process is similarly high), with electricity (for sterilizing the substrate bags and substrates) and hemp shive substrate dominating the results. The hemp shives show different contributions to the impact categories: whereas they are dominating the category land use (81.8% of 19.4 kg Pt eq.) and eutrophication (77.7% of 6.02 × 10−4 kg PO4−3 eq.), their share of climate change is rather low. This can be explained by the fact that hemp is an agricultural product (biotic material), which needs to be cultivated and therefore shows high impacts in categories highly influenced by agriculture, such as land use (area needed for cultivation and associated soil quality), with 90.2% of total kg Pt eq., eutrophication (fertilizer use) with 50.5% of total kg PO43− eq., and water scarcity (irrigation), with 42.6% of total m3 world eq. [39,40]. However, fertilization also impacts acidification, because ammonium fertilizers are frequently used, and the emitted ammonia (to air) is potentially acidifying. Fertilizers also influence the categories of smog, due to emitted nitrogen emissions (to air), and climate change, due to methane and nitrous oxide emissions (to air) from manure and mineral fertilizers, respectively [41]. However, categories such as acidification, climate change, and smog are more influenced by electricity production, mostly due to emissions during coal burning. The German consumption electricity mix was used to model electricity for sterilization, incubation, and drying. It includes, next to a rather small share of renewable and nuclear energy, also a high share of coal [42]. This results in 81.4% kg CO2 eq. of the total global warming potential (GWP100) as well as 58.7% kg SO2 eq. of the acidification potential (AP) and 73.2% kg NOx eq. of the photochemical ozone creation potential (POCP) for one hemp shive composite brick. Further, the substrate bags made out of polypropylene are also a hotspot of climate change, especially for step 3, substrate culture, with 22.5%, but also for water scarcity, where they account for 43.6% of total m3 world eq. in Step 3, substrate culture, because they are based on fossil materials and require high amounts of electricity to be produced. Within the analyzed product system, they also represented the highest amount of plastic used for the entire fungi brick production.
The production step 1, pre-culture, has the lowest impact of all considered impact categories and is mainly influenced by the sterilization of the petri dish and medium. Different to the other production steps, the amount of starting material that needs to be sterilized is very small; thus, the energy required for the sterilization is very low as well.
The impacts of production step 2, grain culture, vary depending on the impact category but are mainly influenced by the rye grain production. Similarly, to the hemp shives, rye as an agricultural product leads to high impacts in the categories of eutrophication (95.2% of total kg PO43− eq.) and water scarcity (84% of total m3 world eq.), but with an overall smaller contribution due to lower quantities applied. Land use impacts of rye are significantly lower compared to hemp shives because the underlying dataset assumes that, due to rye production in Switzerland, the transformation of extensive land use into arable land occurs, which influences soil quality positively. Electricity impacts, due to the autoclave, have an impact on the categories of climate change, acidification, and smog.
Step 4, molding, is mostly influenced by the electricity used to dry the fungi bricks.
Transportation of the substrates and rye grain only play a small role for all considered categories. The modelled transport distances are not large, as it is assumed that the substrates are produced in Brandenburg, which is 50 km away from the production facility in Berlin.
As addressed before, not only hemp shives but also rapeseed straw and poplar wood chips can be used as substrate materials. Thus, the fungi brick production was also carried out and modelled with these two alternative substrates. Changes occur due to the used substrate and associated changes in production step 3, substrate culture. The other production steps do not need to be adapted.
In Table 4, the differences of the entire production of rapeseed straw-based brick and poplar wood chips-based brick compared to hemp shive composite brick in the considered categories are shown. The results of the hemp shive composite brick were set to 100%, and deviations were determined (minus refers to reduced environmental impacts). It can be seen that the differences for the categories of smog, water scarcity, and climate change are small. The biggest changes can be observed for the categories of acidification and eutrophication, as well as land use.
For a more detailed interpretation, the results of production step 3, substrate culture, for the categories of acidification and eutrophication are presented in Figure 4. It is shown that the differences are due to the substrate itself as well as the substrate mix hydration. As shown in Table 2, the amount of wheat white flour and water for hydration differs depending on the used substrate, since water and white wheat flour are added as a percentage by weight of the substrate used. The substrate poplar wood chips perform better than the rapeseed straw and the hemp shives mainly within the cultivation step. Since poplar is a tree, it does not need to be fertilized, whereas rapeseed needs a rather large amount of fertilizer due to its high nutrient requirements [43]. The higher fertilizer use is expressed in higher impacts in the categories of acidification and eutrophication.

4. Discussion

4.1. General Challenges

Regarding the results of this study, it needs to be considered that some energy-inefficient technology on the lab scale possibly led to high energy use. This includes the drying oven in the molding step as well as the incubation room in the substrate culture step. Thus, the environmental impacts associated with electricity use could be reduced if newer technology and improved measurement tools are used.
Furthermore, the data sets used as proxies for the medium components of agar, dextrin, and malt extract might lead to over- or underestimation of the environmental impacts of step 1, pre-culture, and thus, should be modeled with more precise data. However, as their impact on the overall result is rather low, no significant changes are expected.
As mycelium-brick production is localized regionally, consistent use of data sets based on German infrastructure would be required. However, for this study, for some processes Swiss datasets were applied additionally, due to the limited availability in the databases for essential materials, such as rye and wood chips. However, this will not change the fact that the agricultural products have a large impact on eutrophication and land use, according to the utilization of fertilizer as well as monoculture cultivation and therefore soil leaching.
Since the LCA of the fungal-based bricks is a cradle-to-gate study, the use and the end-of-life phase are not analyzed. Due to the biodegradability of fungal-based hemp shive composite bricks, which consist mainly of large quantities of nutrients, there might be an improvement in soil quality after composting. However, it is not yet determined what additional coatings are needed to make the brick fire-resistant. Additional coating might impact its biodegradability. Further investigations into relevant material properties in the construction industry, i.e., durability in general and weather resistance, are needed to confirm the use of fungal-based hemp shive composite bricks in the building sector.
The material properties of fungal-based bricks need to be fully determined in order to develop operational uses and find the most appropriate implementations. Summarized by Jones et al. [16,17], the material properties of fungal-based composites differ by used substrate and fungus, which enables tuning the physico-mechanical properties of these composites by changing substrate composition or adding specific nutrients. The composites analyzed so far are characterized by high acoustic absorption and fire safety as well as low density and thermal conductivity [16]. With these material properties, mycelium composites are suitable for use in construction as insulation material (acoustic and thermal) or interior wall covering. Since a different fungus and substrate were used in this study than in previously published analyses, the physico-mechanical properties need to be evaluated in further tests to make a more specific comparison for the LCA analysis.
In conclusion, it could be noted that the biggest influence was attributed to the electricity used (see Figure 3). Besides the reduction of the overall impact through substitutions in energy supply (respectively, the use of renewable energy sources) and improvements in equipment, mass production of fungal-based materials would also reduce impacts in some process steps and materials.
The presented study focused solely on environmental aspects as an LCA was carried out. However, by also analyzing the other sustainability dimensions, namely the social and economic ones, a more comprehensive picture would emerge. For a product system based on biotic materials, such as agricultural and forestry by-products, competition with other uses of these materials, e.g., use in biogas plants, might occur and leads to challenges in availability. In addition, socio-economic aspects (e.g., trade barriers) can enhance regional as well as global scarcity. Thus, these aspects should be further analyzed (e.g., by applying the BIRD method [44]). Next to the economic dimension, also the social dimension needs to be further analyzed to account for possible social impacts and trade-offs (e.g., by applying the Guidelines for Social Life Cycle Assessment of Products and Organizations [45]).

4.2. Sensitivity Analysis—Industrial Scale-Up

Industrial production would be carried out under different circumstances; thus, assumptions of an industrial scale-up have been made (because a production facility for fungal-based materials does not exist yet) regarding the use of electricity, labor, and materials. In Figure 5, the comparison of results of lab-scale and industrial-scale produced hemp shive composite bricks is shown. It can be seen that the industrial scale performs better in all considered impact categories with the biggest reduction in the category of climate change. Plastic bags in step 3, substrate culture, are not required when substrates will be composted and hygienized in dedicated facilities. The main reason, however, is the reduced electricity use in all steps. Instead of autoclaving, a pasteurization process at 60 °C for 8 h was modeled. Steam boilers for the hygienization of larger amounts of substrate are standard machinery and result in energy savings [46]. According to the costs for steam sterilization of a 400 m2 area (interview, technical manager of Löckes Bio-Vertrieb GmbH) with a price of 0.3 € per kWh, the electricity consumption of 0.0568 MJ for one fungal-based hemp shive composite brick was determined. Further adaptions should consider power measurements of a steam boiler instead of an economical approximation to obtain an accurate assessment of energy consumption. Thermal insulation properties of the building itself were not considered. However, it is assumed that the rented building has an energy certificate of at least A or higher, which would generate minimal energy losses.
Adjustments were assumed for the condensate (80–90 °C) produced due to evaporation in substrate pasteurization, which could be used for room heating or hot water preparation. The drying process of the molding step could be optimized by upscaling in an accessible drying room, which would require 0.0294 MJ per brick. The measured consumption of the dry oven within 1.5 days (Section 2.2) was 21.2% of the maximum power consumption. This ratio was applied to maximum power consumption of the SDR-series drying room, according to the data sheet from Superdry-ToTech [47].
However, it should be noted that in industrial production, higher energy requirements might result from additional machinery, e.g., for shredding the substrate cultures or filling the molds. Consideration of the replacement of work carried out by humans should also be included. Further, the production efficiency should be considered in future assessments.

4.3. Comparison with Other Functional Units/Bricks Used in Construction

Next, the fungal-based composite brick produced at lab scale and industrial scale is compared with conventionally used bricks in construction such as concrete bricks, sand-lime bricks, and facing bricks to gain a better understanding of the overall reduction potentials. The authors are aware, that the functional unit of these bricks differ as conventional bricks are primarily used for the exterior facade of houses and buildings, as they are characterized by properties such as strength, durability, and weather and fire resistance. All these features are not yet sufficiently researched for fungal-based bricks in order to be used for long-term exterior construction.
Since the material properties of the mycelium bricks in comparison to the conventional bricks differ greatly in weight, the comparison was not carried out per kg but per one piece of brick. To determine the respective mass per piece of conventional brick, their respective density (ρconcrete brick = 2.0 kg/m3 [48]; ρsand lime brick = 1.7 kg/m3 [49]; ρfacing brick= 2.1 kg/m3 [50]) and the volume of a normal brick (as described in the functional unit) were applied. Based on their respective mass per piece, the different bricks were compared for the considered impact categories.
Comparing the results of the scale-up brick with the conventional bricks, it can be seen in Figure 6 that the fungal-based brick performs significantly better than the conventional ones in the categories climate change, water scarcity, and smog. Looking at climate change using fungal-based materials instead of concrete might save up to 2.5 times the amount of greenhouse gas emissions, whereas replacing sand-lime bricks or facing bricks might save up to 3–6 times. Due to the use of agricultural products, the eutrophication and land use categories perform considerably worse compared to conventional bricks.

5. Conclusions

The goal of this study was to identify potential environmental impacts of fungal-based brick. Thus, a LCA was conducted for a fungal-based composite brick at the lab scale as well as at the industrial scale. According to the results, the considered impacts are mainly driven by electricity and the agricultural products rye and hemp shives, whereas an industrial scale can decrease energy consumption in particular. Since the industrial-scale analysis is based on several assumptions, the underlying primary data collection should be included in a pursuing study to achieve a more precise assessment.
The LCA analysis further shows a reduction in most impact categories compared to common building bricks. This leads to the presumption that the use of industrially produced fungal-based products as a substitute for previously used building materials might reduce the environmental footprint. However, since many agricultural products are used for production, the study shows an increase in land use and eutrophication. Agricultural products, however, offer the potential for biodegradability and reusability of fungal-based bricks. Recycling as well as durability should therefore be studied in the future, including carrying out a cradle-to-cradle analysis considering the use and end-of-life phase. Additional, alongside the environmental dimension, the economic and social dimensions also should be included in further studies to account for all sustainability aspects.

Author Contributions

Conceptualization, L.S., F.H. and V.B.; data curation, L.S., F.H. and B.S.; formal analysis, F.H. and V.B.; funding acquisition, V.M.; investigation, L.S. and F.H.; methodology, L.S., F.H. and V.B.; resources, V.M. and M.F.; supervision, V.B., V.M. and M.F.; validation, L.S., F.H., V.B. and M.F.; visualization, L.S., F.H. and V.B.; writing—original draft, L.S., F.H., V.B. and B.S.; writing—review and editing, L.S., F.H., V.B., B.S., S.P., V.M. and M.F. All authors have read and agreed to the published version of the manuscript.

Funding

This project was partly funded by the TU Citizen Science project “Mind the Fungi” granted to V.M.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is contained within the article.

Acknowledgments

We acknowledge support by the Open Access Publication Fund of TU Berlin.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Composite bricks based on F. fomentarius grown on hemp shives.
Figure 1. Composite bricks based on F. fomentarius grown on hemp shives.
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Figure 2. Process flow diagram for all four cultivation steps including all inputs to the system. The process system is divided into four major sub steps: 1. pre-culture, 2. grain culture, 3. substrate culture, and 4. molding.
Figure 2. Process flow diagram for all four cultivation steps including all inputs to the system. The process system is divided into four major sub steps: 1. pre-culture, 2. grain culture, 3. substrate culture, and 4. molding.
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Figure 3. Results of one hemp shive composite brick for the impact assessment categories (a) acidification, (b) eutrophication, (c) climate change, (d) land use, (e) water scarcity;(f) smog.
Figure 3. Results of one hemp shive composite brick for the impact assessment categories (a) acidification, (b) eutrophication, (c) climate change, (d) land use, (e) water scarcity;(f) smog.
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Figure 4. Differences of rapeseed straw-based brick and poplar wood chips-based brick compared to hemp shive composite brick over Production Step 3, substrate culture, for the categories (a) acidification and (b) eutrophication.
Figure 4. Differences of rapeseed straw-based brick and poplar wood chips-based brick compared to hemp shive composite brick over Production Step 3, substrate culture, for the categories (a) acidification and (b) eutrophication.
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Figure 5. Comparison of results of lab-scale and industrial-scale produced hemp shive composite bricks, shown in percent.
Figure 5. Comparison of results of lab-scale and industrial-scale produced hemp shive composite bricks, shown in percent.
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Figure 6. Comparison of fungal-based composite brick in lab scale and industrial scale-up with conventionally used bricks in construction: concrete bricks, sand-lime bricks, and facing bricks.
Figure 6. Comparison of fungal-based composite brick in lab scale and industrial scale-up with conventionally used bricks in construction: concrete bricks, sand-lime bricks, and facing bricks.
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Table
Table 1. Impact categories with corresponding characterization factor, category indicator, unit, and applied method.
Table 1. Impact categories with corresponding characterization factor, category indicator, unit, and applied method.
Impact CategoryCharacterization FactorCategory IndicatorUnitApplied Method
Climate change Global warming potential (GWP100)Radiative forcingkg CO2 equivalentsCML [22,23]
AcidificationAcidification potential (AP)Acidification depositionkg SO2 equivalents
EutrophicationEutrophication potential (EP)Deposition N/Pkg PO43− equivalents
Photochemical ozone creation (smog) Photochemical ozone creation potential (POCP)Tropospheric ozone concentration increasekg NOx equivalentsReCiPe [31,32]
Land useSoil quality potential (SQP)Soil quality index, biotic production, erosion resistance, mechanical filtration, groundwater replenishmentdimensionlessLANCA [27,28,29]
Water scarcityUser deprivation potential (UDP)deprivation-weighted water consumptionm3 world equivalentsAWARE [30]
Table
Table 2. Used materials and processes with the required amounts for the production of one fungal-based composite brick, including the applied datasets.
Table 2. Used materials and processes with the required amounts for the production of one fungal-based composite brick, including the applied datasets.
CultureMaterial/ProcessAmount Dataset
Pre-CulturePetri dish0.776 gEU-28 General purpose polystyrene
Petri dish—end of life0.776 gDE: Polystyrene (PS) in waste incineration
Petri dish forming0.00279 MJDE: Electricity grid mix
0.00279 MJDE: Thermal energy from natural gas
Gloves0.546 gDE: Nitril butadiene rubber
Gloves - end of live0.55 gDE: Commercial waste in municipal waste incineration plant
Medium0.0041 gDE: Barley production *
0.00235 gDE: Glycerin by-product rapeseed
0.0128 gDE: dried starch
0.0675 gEU-28: Gelatine from pork skin
0.001 LEU-28: Water deionized
Sterilization 0.0751 MJDE: Electricity grid mix
Incubation0.0008 MJDE: Electricity grid mix
Grain CultureGrain mix20 gCH: Rye grain, fed production, organic *
20 gDE: Gypsum stone
0.02 LDE: Water (desalinated; deionized)
Transport0.0297 gGLO: Truck, Euro 5, 14–20 t gross weight/11.4 t payload capacity
DE: Diesel mix at refinery
Sterilization 0.288 MJDE: Electricity grid mix
Incubation0.0152 MJDE: Electricity grid mix
Substrate Culture (hemp shives)Substrate bags14.3 gDE: Polypropylene-Film (PP) without additives
Substrate bags—end of life14.3DE: Polypropylene (PP) in waste incineration plant
Hemp straw304 gDE: Hemp straw cultivation with catch
Substrate mix hydration0.456 LDE: Water (desalinated; deionized)
13.7 gDE: Wheat white flour
Transport 0.452 gGLO: Truck, Euro 5, 14–20 t gross weight/11.4 t payload capacity
DE: Diesel mix at refinery
Sterilization0,86 MJDE: Electricity grid mx
Incubation0.03 MJDE: Electricity grid mx
Substrate culture (rapeseed straw)Rapeseed straw228 gDE: Rapeseeds (field boarder)
Substrate mix hydration0.342 LDE: Water (desalinated; deionized)
10.28 gDE: Wheat white flour
Transport0.339 gGLO: Truck, Euro 5, 14–20 t gross weight/11.4 t payload capacity
DE: Diesel mix at refinery
Substrate culture (poplar wood chips)Poplar wood chips456 gCH: Wood chips production, softwood, at sawmill *
Substrate mix hydration0.684 LDE: Water (desalinated; deionized)
20.52 gDE: Wheat white flour
Transport0.677 gGLO: Truck, Euro 5, 14–20 t gross weight/11.4 t payload capacity
DE: Diesel mix at refinery
MoldingFoil1.91 gDE: Polyethylene film
Foil—end of life1.91 gDE: Polyethylene (PE) in waste incineration plant
Incubation0.013 MJDE: Electricity grid mix
Drying1.28 MJDE: Electricity grid mix
* ecoinvent datasets.
Table
Table 3. Resulting quantities of one hemp shive composite brick for the impact assessment categories of acidification, eutrophication, climate change, land use, water scarcity, and smog for all four production steps and in total.
Table 3. Resulting quantities of one hemp shive composite brick for the impact assessment categories of acidification, eutrophication, climate change, land use, water scarcity, and smog for all four production steps and in total.
Characterization FactorPre-CultureGrain CultureSubstrate CultureMouldingTotal
Acidification (kg SO2 eq.)2.41 × 10−52.72 × 10−43.63 × 10−42.80 × 10−49.39 × 10−4
Eutrophication (kg PO43− eq.)4.13 × 10−62.45 × 10−43.04 × 10−44.98 × 10−56.02 × 10−4
Climate change (kg CO2 eq.)1.81 × 10−25.68 × 10−22.10 × 10−12.09 × 10−14.94 × 10−1
Land use (kg Pt eq.) 8.10 × 10−25.76 × 10−11.74 × 10+11.29 × 1001.93 × 10+1
Water scarcity (m3 world eq.)1.10 × 10−36.59 × 10−39.42 × 10−34.98 × 10−32.21 × 10−2
Smog (kg NOx eq.)1.91 × 10−51.02 × 10−42.46 × 10−42.16 × 10−45.83 × 10−4
Table
Table 4. Differences between composite bricks based on rapeseed straw or poplar wood chips compared to composite bricks based on hemp shives in the considered categories.
Table 4. Differences between composite bricks based on rapeseed straw or poplar wood chips compared to composite bricks based on hemp shives in the considered categories.
Impact CategoryDifferences Compared to Hemp Shives Composite Brick over the Entire Production (in %)
Rapeseed Straw-Based BrickPoplar Wood Chips-Based Brick
Acidification33.37%−7.56%
Eutrophication21.14%−49.40%
Land use−17.31%31.29%
Climate change2.19%0.61%
Water scarcity0.31%6.35%
Smog−2.79%0.01%
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Stelzer, L.; Hoberg, F.; Bach, V.; Schmidt, B.; Pfeiffer, S.; Meyer, V.; Finkbeiner, M. Life Cycle Assessment of Fungal-Based Composite Bricks. Sustainability 2021, 13, 11573. https://doi.org/10.3390/su132111573

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Stelzer L, Hoberg F, Bach V, Schmidt B, Pfeiffer S, Meyer V, Finkbeiner M. Life Cycle Assessment of Fungal-Based Composite Bricks. Sustainability. 2021; 13(21):11573. https://doi.org/10.3390/su132111573

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Stelzer, Lisa, Friederike Hoberg, Vanessa Bach, Bertram Schmidt, Sven Pfeiffer, Vera Meyer, and Matthias Finkbeiner. 2021. "Life Cycle Assessment of Fungal-Based Composite Bricks" Sustainability 13, no. 21: 11573. https://doi.org/10.3390/su132111573

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