Our research

Material flows transition and social adaptation

Objectives and overview

The objectives of Project 1 (PJ1) are to explore the long-term direction and adopt science-based targets (SBTs) for material flow transition towards planetary health, and to design measures that will help society to adapt to the transition, with a focus on the supply chains of materials, infrastructure, and consumption. To this end, the project focusses on the development of "material-flow-nexus models", which are computational models (e.g., input-output models, stock-flow models, and statistical models) that can be used to analyze the environmental and social impacts associated with material flows in society.

Using these material-flow-nexus models, we will examine the dynamics of material availability under future environmental constraints for determining SBTs for materials, and identify environmental hot spots within material supply chains in order to prioritize the implementation of technological measures. The models also illustrate the lifestyle changes that will need to be adopted by society in order to meet sustainability targets. The project will contribute to the accumulation of scientific knowledge in areas related to the design of transition pathways for material flows, leading to planetary health.

Research plan

In the first three years (FY2021–2023), we will analyze the current status and historical changes in material flows and quantify the diverse impacts of the flows on planetary health; this will clarify the structural relationship between the material flows and their impacts. Then, by using those results to develop the material flow nexus models, a methodological foundation for long-term scenario analyses will be consolidated. By 2025, we will have compiled data on major production technologies, consumption patterns, and their effects on material flows/stocks according to different future scenarios. In addition, it will be possible to estimate “material budgets” until 2100 by considering the type of materials, and explore the optimal temporal allocation of the budgets for each scenario. The material budget is an analogue of the carbon budget, and refers to the maximum amount of materials that could be available at a global level under a given set of environmental constraints and their effect on planetary health.

We will illustrate global and Japan's long-term goals regarding material productivity and material circulation by considering material budgets and propose policy indicators for monitoring progress and for identifying gaps in achieving these goals. Furthermore, we will focus on material efficiency improvements by decoupling consumption and material use, examine the sufficiency and acceptability of consumer needs, and propose lifestyle adaption measures as they relate to consumption by society in order to achieve these goals.

Expected outcomes

Scientific knowledge on the transition of material flows will be compiled to assess planetary health, and will be disseminated in the form of opinion papers. Through these activities, the project will support producers and consumers to manage material flows effectively and achieve SBTs for materials.

Major achievements

FY2021

[1.1] Establishment of material use reduction targets to realize a decarbonized society

We developed a global-scale simulation model to quantify flows and stocks of six major metals—iron, aluminum, zinc, lead, nickel, and copper—and formulated a long-term outlook and “material budgets” (i.e., maximum amount of materials that could be available at a global level under a given set of environmental constraints and their effect on planetary health) required for the transition to a decarbonized society. By analyzing metal use around the world over the past 110 years (1900-2010), we found that the current economic activities in high-income countries, including Japan, are sustained by approximately 12 t/capita stock of metals. The value is much larger than the global mean value of approximately 4 t/capita, and 1 t/capita or less in low-income countries. This indicated that inequalities exist in the global metal use. Our study was the first to present numerical data to show these inequalities.

We also examined whether the current metal production and use levels of high-income countries are achievable at the global level, given the current constraints on GHG emissions. Our analysis found that with these constraints, production of the six main metals from natural ores will peak before 2030, and that total cumulative demand for these mineral ores in the 21st century will remain at about 50% or less of the current proven reserves. This suggests that future supply of metal resources from natural ores can be reduced by the GHG emission constraints even before their physical depletion. In this case, world average per capita stock (i.e., availability) of metals of all the scenarios was estimated to be approximately 7 tonnes, which did not reach the current level of high-income countries (12 tonnes). The model also calculated the same as about 10 tonnes under a variety of ambitious measures for improving resource efficiencies (e.g., transition to decarbonized power generation, enhancement in energy efficiency and promotion of recycling), which was also below the high-income county’s level. These results showed that keeping global metal production and consumption at the high-income country’s level will be difficult. These findings highlighted the importance of satisfying basic needs (e.g., housing, transport and communication) with lower levels of metal production and consumption, in addition to developing decarbonized production technologies.

[1.2] Consumer carbon footprint analysis and listing of social adaptation measures

To provide information on possible lifestyle changes toward a decarbonized society, we developed a carbon footprint database that considers local characteristics to quantify effects of social adaptation measures across various consumption sectors. This type of database is the first in this field. After reviewing internationally available literature and the latest analysis of “hotspots” (i.e., the fields that currently have higher carbon footprints than others), we identified 65 options for decarbonized lifestyles on the demand side across a wide variety of sectors including housing, mobility, food, consumer goods and services, and leisure domains. Further, in order to reflect specific local characteristics, the carbon footprint database considered different local commodity prices as well as household consumption data of approximately 500 items in 52 Japanese cities (prefectural capitals and cities designated by government ordinance). We conducted a scenario-based analysis using this database, and quantified potential carbon footprint reduction by lifestyle changes in different regions. These results were compiled into a booklet to facilitate intuitive understanding of general readers (Fig. 1).

The analysis results showed that there can be as much as a five-fold difference in carbon footprint reduction effects between the target cities, depending on their choices of mitigation measures (e.g., 192−851 kgCO₂e for ridesharing; and 120−280 kgCO₂e for extended use of clothes). We highlighted the importance of prioritizing policy measures according to regional differences. Toward the “planetary boundary” goal, we conducted a scenario-based analysis to identify transition pathways for achieving the decarbonization target of keeping carbon footprints of per capita household consumption below 3.2 tCO₂e/cap/year that could limit global temperature rise to 1.5 °C. The lifestyle options were examined after being categorized into two groups: measures for ensuring sufficiency (e.g., encouraging changes in consumption mode and behavior) and those for improving efficiency (e.g., introducing equipment and technologies to households). The results showed that a wide range of behavioral changes as well as introduction of technologies that improve resource efficiencies will be indispensable for achieving the global target.

[1.3] Exploration of innovative pathways for material flows through evaluating the effects of material production and use on human health

Human health is an integral part of planetary health. We examined impact of consumption in one country on other countries’ human health damage. Specifically, we quantified nation-wise primary and secondary PM_2.5 (i.e., particles with an aerodynamic diameter of 2.5 μm or less) emissions induced by consumption that are responsible for global mortality. As a first step, we linked a global multi-regional input-output (MRIO) model with emission inventory maps to map out emissions of PM_2.5 primary particles (black carbon, organic carbon, and other components) and secondary particle precursors (nitrogen oxides, sulfur dioxide, ammonia, carbon monoxide and non-methane volatile organic compound) that are induced by consumption (i.e., domestic final demand) in 19 member nations of the G20 (i.e., countries eligible for the G20 summit presidency) and global supply chains for the year 2010. Next, using an atmospheric chemical transport model, we estimated concentrations of consumption-derived PM_2.5 in the atmosphere. We also estimated the number of premature deaths resulting from exposure to PM_2.5 using an integrated exposure-response (IER) model and population distribution data by sex and age.

The results showed that exposure to PM_2.5 that was induced by the consumption of these 19 countries accounted for approximately two million premature deaths annually around the world. These deaths included approximately 80,000 infants (under five years of age), which lowered the average age of death to 67. Of the 19 nations, consumption in China and India, two highly populous countries, contributed the most to the PM_2.5-related premature deaths, each contributing to 910,000 and 490,000 deaths respectively. However, production in the same two countries caused more PM_2.5-related premature deaths, 1.09 million and 550,000, respectively. This indicated that, in China and India, production had higher impacts on PM_2.5-related premature deaths than consumption did. In other words, more PM_2.5-related premature deaths were caused in these two countries by supporting consumption abroad. However, in the countries with higher level of incomes, such as Japan, the United States, the United Kingdom, Italy, and France, consumption had higher impacts on PM_2.5-related premature deaths than production did. In these countries, the negative impacts of production have been minimized, due to the government’s air pollution control measures and higher levels of medical and public health services. Thus, consumption in the high-income countries, together with their import, had substantially higher impacts on PM_2.5-related premature deaths in developing countries.

For example, we found that consumption in Japan in 2010 was responsible for about 42,000 premature deaths at an average age of 70 at home and abroad, of which those abroad, including China and India, accounted for 74%. This means that annual per capita consumption in Japan caused 0.00033 premature deaths, and its lifetime consumption caused 0.027 premature deaths assuming that Japanese population’s consumption level remains the same until they become 84 years old which is the country’s average life expectancy. To put it another way, lifetime consumption of every 36 Japanese people led to the premature death of one person per year abroad. On the other hand, we estimated that production in Japan in 2010 was responsible for 17,000 PM_2.5-related premature deaths at an average age of 76 at home and abroad. This means that, in Japan, consumption triggered PM_2.5 related premature deaths more than production did, in terms of the number of deaths (42,000 vs. 17,000) and the average age of death (70 vs. 76). These findings suggested that there will be more opportunities for Japan to reduce premature deaths through enhancing air pollution control on the consumption side, in addition to the conventional measures on the production side.

[1.4] PJ1 team’s other outreach and networking activities

As for our outreach activities, we published English-language science animation video clips as a new way of disseminating our research findings and stimulating policy dialogue about them in addition to academic papers and magazine articles. For networking in Japan, we have provided information and lectures on our macroscopic outlook and scientific target setting for the future of material flows, upon request by private companies and specialized institutions. These activities have enabled us to establish professional networks to ensure application of our research outcomes in real world. Internationally, we provided these findings to “Global Material Flows and Resource Productivity,” a report of the International Resource Panel of the United Nations Environment Programme (UNEP).

For providing information about consumer lifestyle options, we set up a website (lifestyle.nies.go.jp) as an interactive visual tool for citizens, local governments, and regional organizations to supplement our academic papers. A unique feature of this website, that considers regional differences and quantifies concrete measures for major aspects of our daily lives such as food, clothing, and housing, attracted considerable media attention in Japan.

In the area of policy implementation support, we provided basic data to assist the Ministry of the Environment (MoE) in quantifying the impact of local actions for creating zero carbon cities in Japan. We also helped municipalities and citizen groups to formulate decarbonization lifestyle scenarios through workshops. Specifically, together with the Institute for Global Environmental Strategies (IGES), we facilitated utilization of our data and estimation techniques through workshops for two Japanese cities (Yokohama and Kyoto) as well as those for citizen groups overseas (Thailand, India, Brazil, and South Africa).

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Chemical management for material flows transition

Objectives and overview

Project 2 (PJ2) aims to establish a scientific framework for the effective management of chemical substances and environmental pollutants in order to facilitate the transition in material flows and improve planetary health. To achieve this objective, we will provide evaluation frameworks and analysis methods in the following areas: understanding the behaviors of chemical substances and environmental pollutants especially through the material cycles; identifying the factors that hinder the material flows transition; and proposing measures to eliminate these factors to promoting the material flows transition.

We will conduct a series of case studies in order to examine the validity of these frameworks and methods. The subjects of the case studies will include plastics and other materials containing persistent organic pollutants (POPs), including flame retardants (BFRs) and polyfluoroalkyl substances (PFAS); metal-containing products, such as durable goods; recycled construction materials containing heavy metals; and environment-polluting marine plastics and microplastics. Each case study will identify specific points and causal factors that hinder the transition to the new flows of the materials concerned, and will be used to propose measures to eliminate these hindering factors.

Research plan

In the first three years (FY2021–2023), we will develop future scenarios for recycling materials and products such as plastics, metal-containing products, and recycled construction materials to reflect current and potential future societal requirements. We will analyze the behavior of chemical substances, marine plastics, and microplastics during the key processes of recycling etc. under a variety of future scenarios and develop a model to analyze the flows of chemical substances within the economic sphere and the emission of pollutants into the environment.

In the following two years (FY2024–2025), we will perform system analyses based on these future scenarios and the results of behavior analysis. The analyses will incorporate the material flows and emission inventories from studies, and will identify factors that hinder transitions in material flows. These factors will be identified by reviewing the changes in different standards and regulations (e.g., legal controls, risk management levels etc.), and we will further develop scenarios in which different measures are implemented in order to manage chemical substances and environmental pollutants in a way that will not limit the transition to the new material flows.

Expected outcomes

The project activities are expected to lead to the establishment of a scientific review scheme that will suggest possible ways in which chemical substances and environmental pollutants can be managed in a way that can be harmonized with the transition to desirable material flows in the future. The project is expected to contribute to the development of integrated policies for both material flows and managing both chemical substances and environmental pollutants.

Major achievements

FY2021

[2.1] Identification of chemicals that hinder material flows transition

We identified and categorized hazardous chemicals that potentially hinder recycling of plastics and construction materials. For plastics, we examined overlaps between the items of a hazardous plastic additive (approximately 400) list published by the European Chemicals Agency (ECHA) and hazardous chemicals in plastics reported by other governmental institutions. It revealed that there were 20 overlapped chemicals that potentially harm the environment and hinder recycling. These 20 chemicals included the substances that are already regulated internationally or those of very high concern listed by the European Union (EU)’s REACH (registration, evaluation, authorisation and restriction of chemicals) regulation: decabromodiphenyl ether (BDE-209), hexabromocyclododecane (HBCD) and chlorinated paraffins (CPs) (flame retardants listed as POPs by the Stockholm Convention); UV absorber (UV-328) (a POP candidate); and phthalate esters (plasticizers), lead oxide sulfate and lead chromate (heat stabilizers and pigments) whose use in electrical and electronic equipment is regulated by the European Restriction of Hazardous Substances (RoHS) Directive. These findings led us to plan our next activities: reviewing the current state of concentrations and flows of these hazardous substances in plastic products and waste; and understanding their behavior in recycling processes.

Regarding construction materials, environmental standards for soil can be a hindering factor for recycling them if the standards are made tighter or if new substances are added to the current list. The standards for soil are often referenced in determining feasibility of recycling them. We reviewed drinking water quality standards (DWQSs) of other countries, especially the substances they cover, because they are referenced as a basis for other environmental standards. Since Japan is also likely to reference these lists for modifying domestic environmental standards, we reviewed DWQSs and guidelines of the EU, the U.S., Australia, Canada, China, South Korea, and the World Health Organization (WHO), and identified commonly-regulated substances such as antimony and barium that Japan had not yet included in its DWQSs. If they are added to Japan’s DWQSs, recycling of construction materials is likely to be affected, depending on the level of their DWQS values. We examined the current state of concentrations of these chemicals in approximately 50 recycled construction materials, and evaluated their release to the surrounding environment using leaching test methods that were generally adopted in Japan. These results will enable us to further examine whether setting certain criteria levels for these substances inhibits the use of recycled materials. Environmental standards for soil at a similar level as DWQSs can be too strict for determining safety of recycled construction materials. For this reason, we confirmed a strong need to establish new risk assessment methods based on appropriate evaluation of chemical exposure and risk in the use of such materials.

[2.2] Understanding of the current status of pollutants contained in products and waste

Polybrominated diphenyl ethers (PBDEs) are known as brominated flame retardants (BFRs) that have widely been used in electrical and electronic equipment (EEE) casings and textiles. The production and use of PBDEs and sales of products containing them have been banned internationally through their inclusion in the lists of the Stockholm Convention and the RoHS Directive. PBDEs are among the hazardous substances that potentially hinder recycling of plastics. Having considered this importance, we chose them as target materials for our study, and examined their concentrations in recycled plastic products.

We sampled 540 products (total of 1139 components) of plastic toys and household items from 18 countries (mostly Japan) during the period from 2015 to 2019 and evaluated their PBDE concentrations. First, as an indicator of PBDE content, bromine concentration of each part was measured using a portable X-ray fluorescence spectrometer. The results showed that 219 parts, or 20% of the total, had bromine content of more than 30 mg/kg. Then, we analyzed PBDE content in these samples using gas chromatography–mass spectrometry (GC-MS). PBDEs were detected in 109 parts, or about 10% of the total. Among them, the most common substance was BDE-209 (i.e., deca-BDE). These 109 parts included black plastic toys, accessories, hangers, bookends, flashlights, and hair clips. Their PBDE content ranged from 35 to 10,000 mg/kg. Since these values were far less than the amount (i.e., from several percent to about 10% of the item’s weight) required to ensure flame retardancy, it is unlikely that the PBDEs found in these samples were intentionally added to make the products less flammable. Flame retardancy is generally not required for these products. Instead, our results implied that some of these items were produced from plastics that were recycled from waste EEE containing PBDEs, and that these products were contaminated by PBDEs accidentally. The need of preventing such unintentional contamination is expected to increase because Japan’s newly-enforced plastic resource circulation law (i.e., the Act on Promotion of Resource Circulation for Plastics) encourages manufacturers to collect used plastic-containing products and recycle them.

In order to promote circulation of plastic resources, it is important to eliminate PBDEs in their recycling processes and appropriately control accidental contamination by them. Our findings have highlighted that in order to maximize the recycling of plastics while properly managing PBDEs, it is necessary to optimize the level and the point of determination as PBDEs-containing waste in the recycling process. For these purposes, behavior of PBDEs in each recycling process needs to be fully understood as their understanding will form a basis for further analyses.

[2.3] Development of analytical methods for [2.2] (Understanding of the current status of pollutants contained in products and waste)

We developed methods for analyzing PFASs in waste and end-of-life products, and applied them to investigating PFAS content in commercially available water- and oil-repellent agents. First, we reviewed existing analytical methods for perfluorooctane sulfonate (PFOS) contained in waste and PFOA contained in drinking water. Then, after clarifying scope of these methods, we optimized them for applying to a wide variety of PFASs and waste samples. These optimizations led to establishment of analytical methods for concentrations of 73 types of PFASs contained in waste and end-of-life products (e.g., water- and oil-repellent products), including the ones listed in the Stockholm Convention and the Methods 533 and 537.1 of the U.S. Environmental Protection Agency (EPA). Among them, our achievements included development of a method for indirectly analyzing fluoropolymers, the primary source of PFOA. This was a milestone for fluoropolymer analyses as there was no method in the past for directly analyzing them due to difficulties associated with pretreatment of samples and adjustment of measuring equipment. We employed hydrolysis treatment of fluoropolymer side chains under alkaline conditions and quantified degraded PFOA-related compounds. The above-mentioned scientific results, issues, and points to note for PFAS-related analysis were shared with a MoE working group on development of testing methods for waste containing POPs.

Next, these analytical methods were applied to examine actual PFAS content in a total of 54 water- and oil-repellent agent products sold before (2011) and after (2021) the inclusion of PFOA in the Stockholm Convention. The results revealed that 5 out of 28 products sold in 2011 contained PFOA-related compounds (up to 96 mg/kg) as synthesis‐related impurities that exceeded the proposed limit (50 mg/kg) for PFOS and PFOA in the Basel Convention technical guidelines. We also conducted hydrolysis treatment of fluoropolymers that compose water- and oil-repellent agent products to quantify decomposition products of PFOA-related compounds. Again, the levels of PFOA-related compounds (up to 8,100 mg/kg) in 10 out of 28 products sold in 2011 and in 5 out of 26 products sold in 2021 exceeded the limit value (50 mg/kg) of the guidelines. This concluded that some commercially available water- and oil-repellent agents and related products contain synthesis-impurities and decomposition products of fluoropolymers, which can be sources of PFOA, at the concentrations higher than the proposed limit value of the Basel guidelines.

It should be noted, however, that detection of PFOA-related compounds for waste products using water- and oil-repellent agents is much more difficult than that for waste products made of the agents themselves (e.g., sprays). This is because the agents are used for a wide range of products, including clothing, interiors, leather, and paper. As emissions of PFOA-related compounds into the surrounding environment during waste treatment processes (e.g., cleaning, sorting, heating, molding, and incineration) is a serious concern, we proposed a survey on these processes at waste treatment and resource recovery facilities. Discarded water- and oil-repellent products are collected as general and industrial wastes and treated at these facilities. The proposed survey is important for ensuring appropriate treatment of wastes containing PFOA-related compounds.

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Material circulation and sequestration technology

Objectives and overview

The objective of Project 3 (PJ3) is to develop, on the waste treatment/disposal side, material recycling/sequestration technologies and systems that can adapt to the transition in material flows on the production side, and to propose transition methods for realizing planetary health. More specifically, the project will develop carbon recycling technologies and systems that lead to negative carbon emissions, and pollutant-sequestration technologies that can be applied to waste management. Steps for introducing these technologies will be presented in the form of a roadmap, which will consider social factors and contain appropriate policy mechanisms and financial plans for their introduction.

The project covers three sub-themes. The first sub-theme involves the development of new technologies and systems for recycling, proper disposal, sequestration of hazardous substances to respond to the transition in material flows from the perspective of effective waste management. To that end, a variety of scenarios will be formulated and examined to identify the most appropriate pathways (i.e., time, place and scale) for introducing these systems, and for transforming the existing waste processing systems. The second sub-theme deals with development of recycling technologies in conjunction with a system to convert bio-based waste into energy and valuable materials with negative carbon emissions. The second sub-theme will also focus on ensuring safety and reducing pollution through the conversion processes. The third sub-theme addresses the development of long-term storage/isolation/disposal technologies to improve the safety of recycled materials and reduce negative impacts of hazardous substances on the global environment.

Research plan

In the first three years (FY2021–2023), we will focus on kitchen and plastic waste to identify optimal production and consumption patterns that enable carbon-negative emissions in recycling and treatment processes. With the aim of converting biomass-derived consumer products to carbon stocks, we will verify the methods and requirements required for converting residues via thermal decomposition of biomass or organic waste to sequester carbon in the soil and in construction materials. In parallel, by linking thermal gasification and fermentation processes, the project will build integrated systems that convert derived gases, such as carbon dioxide (CO₂) and carbon monoxide (CO), into fuels. Further, mathematical models will be developed for evaluating the emission-control functions of the long-term storage and disposal technologies, and systems designed to isolate harmful substances from the environment.

In the following two years (FY2024–2025), a roadmap for the transition will be developed with detailed plans (e.g., time, place and scale) for realizing production, consumption and waste management systems that can contribute to the transition of material flows. With regards to ensuring the safety of carbon storage, the project will assess the presence/absence of hazardous chemical substances and other pollutants in thermally treated waste residues, and demonstrate the most applicable methods for curbing environmental emissions. In addition, the project will establish integrated systems for converting the derived CO₂ and CO gases into chemical products, and demonstrate how interactions between recycled inorganic materials and living organisms can promote carbon fixation. Based on the results of these studies, we will evaluate the application of these technologies to the integrated regional treatment of recyclable materials, as well as evaluating their negative carbon-emission effects. Further, we will propose basic conditions for efficiently managing and maintaining the mechanisms for isolating hazardous substances.

These findings will be presented as guidelines for distinct risk scenarios, from the perspective of the material's transportation and structural stability. Finally, the project will examine how environmental risks can be reduced in the extreme long term, as well as how sound material flows can be ensured through the application of these technologies under the proposed conditions.

Expected outcomes

Through these developments, the project will present optimal pathways for consumption and production, as well as down-stream material flows, all focused on the goal of realizing a carbon-neutral society by 2050. The project team will examine the developed technologies and develop the roadmap for regional decarbonization through collaboration with the local community. These results are expected to be promoted and integrated into the core operations of local municipalities with the aim of establishing a sound material-cycle society. Upon completion of the project, technologies and systems of long-term storage and management of hazardous substances will have been established, which will contribute to the safety of the regions in which these substances are managed as well as reducing global carbon emissions. The research results are also expected to provide a scientific basis for drastically altering the requirements for managing specially controlled waste and ensuring its safe disposal.

Major achievements

FY2021

[3.1] Development of waste treatment technologies for carbon storage and utilization

Pyrolysis treatment is one of the alternative technologies of waste management to the incineration technology currently used. The technology can flexibly control products such as carbonaceous char, oil and inflammable gas generated by processing biomass-derived waste (e.g., garden waste). We examined technical feasibility of expanding feedstock options for this technology as a part of our activities to propose decarbonization of the processing and recycling technologies required for material flows transition. Specifically, we analyzed different compositions of biomass-derived waste to examine causal factors that affect thermal decomposition characteristics and to evaluate their influences on differences in decomposition efficiency.

We conducted thermogravimetric analyses (TGA) on various plastic products such as bio-degradable polymers (BDPs) and biomass-based polymers (BBPs) as well as different biomass materials and additives. Through these analyses, we clarified the temperature (Tmax) at which their thermal decomposition rate was maximized. For example, their Tmax values were found to be as follows: approximately 300 °C for biowaste (e.g., agricultural residue and food waste); from 285 °C to 400 °C for paper, diapers, and BDPs such as polylactic acid (PLA); and from 440 °C to 480 °C for BBPs such as biopolyethylene. The maximum difference in Tmax between BDP and BBP was 200 °C. By conducting preliminary biological methane production tests on each BDP, we found that substances like PLA and polybutylene succinate, which are slow to decompose and difficult to ferment efficiently, are well suited to pyrolysis treatment. To evaluate the thermal decomposition efficiencies of each material, we calculated reaction parameters such as activation energy (Ea) using Friedman analysis. The Ea values obtained in this analysis ranged from 20 to 340 kJ/mol, and the groups with higher Tmax values also tended to have higher Ea values. The Ea values of BBPs were ten times greater than those of biowaste, while those of BDPs and paper were intermediate values between the two.

These reaction parameters made possible simulation of thermal decomposition of each material. It enabled estimation of thermal decomposition rates with different treatment conditions (e.g., temperature and retention time). Although still being a prototype, this simulation model can verify various thermal decomposition technologies that are currently being developed commercially. The model can also be applied to review the effect of waste flow changes on thermal decomposition and estimate per weight unit energy consumption of pyrolytic treatment of various materials. Since characteristics of thermal decomposition of biomass-derived materials and products are not well known, the obtained fundamental data are valuable. We also noted that, in our analysis of various products using Fourier-transform infrared spectroscopy (FT-IR) method, some composite materials were found to contain impurities although they were all classified as plastics. The presence of these impurities suggests their potential influences on thermal decomposition behavior and reaction rate parameters. Such influences and mechanisms need to be further analyzed as a next step.

The above results showed that, if low-temperature thermal decomposition (i.e., low-temperature carbonization) processes are applied, the treatment temperature can be lowered to 350-400°C (500°C lower than incineration) by switching raw materials from petroleum-derived plastics to BDPs or paper. These findings indicated that such a change in materials will potentially reduce energy input for the treatment processes, thereby further reducing CO₂ emissions. We started measuring enthalpy changes during thermal decomposition processes using a technique referred to as differential scanning calorimetry to quantify CO₂ reduction effects. However, in these low-temperature processes, fluorine-based formulations (i.e., substances identified in PJ2 that hinder material flow transition) and petroleum-based plastics may be left in carbonaceous char residues, which poses a concern. These materials can become environmental pollutants, and can hinder non-combustion use of the char. Our findings on thermal decomposition characteristics of these hindering materials can be utilized to propose, jointly with PJ2, appropriate criteria for accepting each type of biomass-derived waste for thermal treatment according to the relationships between temperature, retention time, and decomposition rate. Since currently available thermogravimetric analysis or differential scanning calorimetry methods can not precisely determine properties of generated char, pyrolysis gas or codensate impurities, usability of these materials could not be fully examined before. We developed a thermal decomposition system capable of evaluating properties of materials generated in the treatment processes. Using this system with FT-IR or with other instruments, we have started our analysis of char properties including their surface area and functional groups. In parallel with this, we have started to study effects of impurities on thermal decomposition of mixed materials. We found that the surface area of carbides increased two to four times when biomass-derived materials are mixed with certain BDPs. This indicated that functionality of carbides can improve when certain alternative materials are used in the treatment. These new findings are expected to contribute to development of more efficient new technologies.

[3.2] Development of sequestration technologies for hazardous substance management

We constructed a mathematical simulation model to evaluate the functionality of isolated final disposal sites in controlling hazardous substances. Using this model, we evaluated long-term (approx. 100 years) behavior and transport of lead and chromium (Fig. 2).

In the model, aging-related deterioration and seismic damage of facility structure; concentrations of hazardous gases in the facility; dissolved oxygen (DO) concentration; and degradation and biochemical transformation of the waste containing lead and chromium and associated changes in their leaching behavior were considered. We targeted two types of disposal facilities, isolated disposal facilities above ground (Type-A), and isolated disposal facilities underground (Type-B). We set different scenarios with the following conditions: aging, seismic motion, submergence (for Type-B only), presence of artificial barriers (e.g., bentonite layer) to prevent degradation, mineralization and leaching of hazardous substances into the surrounding environment. Our simulation results showed that CO₂ emission from the waste treated in the facility is expected to increase substantively with aging of its structure. We also projected that exposure of floor slabs to high concentration (e.g., approximately 40% after one year) of CO₂ in the facility could start to cause cracks in the slab concrete after 10 years and emit lead and chromium through them into the surrounding environment regardless of whether these cracks are caused only by the exposure or with seismic motion. The waste-derived CO₂ and salt can also cause corrosion of reinforcing steel in the site’s external periphery separating facility if the facility’s surface is in direct contact with the landfilled waste and if it is not adequately covered with water/corrosion protection materials. With the corrosion rate of 100%, the crack widths in the floor slabs were estimated at 19 to 27 mm (i.e., 38 to 54 times bigger than the permissible crack widths for commonly used reinforced concrete structure). As the floor slabs are exposed to high chloride ion concentration up to 70 g/L, the corrosion rate after 10 years is projected to reach 100%. Thus, in order to maintain high performance in the functionality of isolating hazardous substances, it was found that effective measures such as controlling landfill gases (i.e., waste-derived CO₂) and coating concrete structures with appropriate water/corrosion protection materials would be necessary.

Another important finding was that artificial barriers cannot ensure sufficient performance in retarding chromium migration into the surrounding environment compared to that for lead. The model estimated that chromium migrates to the environment approximately 5.1 to 8.7 m over 100 years for Type-A facilities above-ground. In the case of Type-B facilities underground, on the other hand, the crack widths are smaller (i.e., 1 to 6 mm) than those of above-ground facilities because the earth pressure around the facilities confines the structure and suppresses the occurrence of cracks. Moreover, our results showed that Type-B facilities allow only a small amount of lead and chromium to leak out to the environment and that their travel distances are shorter (e.g., 10 m for chromium and 1 m for lead at most, except in the case of submergence). However, as Type-B facilities have a higher risk of being submerged due to torrential rains or temporary rise in groundwater level, both lead and chromium can migrate longer distances (approx. 25 m for chromium) during such events. These results highlighted the importance of properly designing artificial barriers for controlling migration of hazardous substances over a long time based on their properties and requirements for each type of facility structure.

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