*Editorial* **Theoretical and Practical Approaches of Circular Economy for Business Models and Technological Solutions**

#### **Csaba Fogarassy 1,\* and David Finger <sup>2</sup>**


Received: 12 June 2020; Accepted: 18 June 2020; Published: 22 June 2020

**Abstract:** Circular solutions are essential to tackle the imminent challenges of depleting resources and emerging environmental problems. The complex nature of material and energy systems and the changing economic and technological conditions depend on regional settings and accordingly result differently in developed and rapidly developing countries of the world. A wide variety of theoretical approaches can be used to facilitate a shift from the linear use of resources to circular systems, e.g., circular product planning, zero waste management, service-based repairing, refurbishing, and remanufacturing, to name just a few. The introduction and examination of circular solutions can be based on theoretical models in order to guarantee and ensure a successful application. The successful application of innovative technology approaches, business solutions, and organizational development can be facilitated through theoretical models and new scientific results that support innovation processes. The presented article focuses on sustainable and innovative methods that help and enable the proper use and recovery of resources.

**Keywords:** circular solution; environmental assessment; product lifecycle; sharing economy; short supply chain; biomass utilisation

#### **1. Introduction**

The concept of the circular economy has become well known and researched through the European Union's Action Programs in recent years, but its scientific foundations and other system solutions have long been known. The context of the application of circular economic systems, i.e., the economic and technological environment of the introduction of new solutions, allows the development of very novel solutions [1]. The use of digital tools has opened up new opportunities and wide gates for businesses to follow consumer needs accurately, discover new market opportunities, explore new ways to connect with customers, and build fast and low-cost profiles in their sourcing and sales channels [2]. The change also means that it is not product development or organizational development that becomes the most important factor in corporate competitive processes, but the improvement of product marketing and sales mechanisms [3]. The basis of the circular economic concept is therefore not classical, Schumpeterian typology, product, technological, marketing or organizational innovation, but the re-dimensioning of business processes and models, i.e., business model innovation. Irrespective of the EU Circular Action Programs, the application of circular transformation and feedback system models has already started in business, the phenomenon can also be traced during the development of business models in different sectors (biotechnology, informatics, transport).

In circular economic theory, the primary goal is not to create cycles of material and energy flows (these are largely known), but to transform business processes into sustainable, closed-loop resource systems. As long as the basic mechanisms of business models and business innovation planning do not support circular operating principles, material and energy flows cannot be operated in closed cycles [4]. EU circular action programs can therefore provide good direction and financial resources for the introduction of sustainable business models, but unfortunately the scientific basis, the appropriate research background, the necessary and credible databases, and their thorough and scientific analysis, are not yet an active part of the current linear circular transformation processes [5]. Typically, in circular economic models, economic actors and members of the supply chain integrate their resources with each other, so that business ecosystems can constantly redesign themselves, i.e., operate dynamically and potentially in self-regulatory systems [6]. While in traditional supply chains, i.e., according to the linear business model, permanent roles are assigned, in the cyclical model we can talk about developing, dynamic and potentially independent actors who together create circular value flows in interaction with each other. The phenomenon can be visualized in a similar way to the form of the Archimedean spiral, in which the individual circles always remain circles but move to an ever-higher level on the scale of values.

Thus, according to the new business models, in the circular economy, we no longer talk about value chains, but circular value circle, because these value ranges contain the full spectrum of activities performed by different actors: a product or a service is not only delivered to the user, but its remnants (material and energy) are also transported back into the system. The different values and innovative elements are shared by the actors of each value group, so the existence of a wide-ranging system of relations and cooperation becomes especially important [7,8]. Such a degree of cooperation requires the use of digital decision support or data analysis technology systems, where the use of BigData systems, Internet of Things (IoT) or Artificial Intelligence (AI) systems becomes a basic criterion. Despite the fact that circular business model innovation is one of the development priorities of the European Union, currently interpreting the concept of circular economy and managing it in the right place is also a challenge, and market transformation research related to the field is an absolute novelty in the field. The key scientific challenge is to answer the following questions: how can business models of circular economic systems be successfully designed? What are the specific frameworks that can underpin sustainable business solutions in each sector? What sectoral and other specificities can be explored in the design and modeling of circular systems?

#### **2. Theoretical and Practical Approaches**

The popularity of the concept of the circular economy is different from any of the policies of the European Union, so it is worth treating it as a special phenomenon. The circular economic model presented in the action program is essentially an industrial service system that replaces the classic, one-way life cycle concept by offering to redesign material flows by helping to use renewable energy sources. Its main goal is to get rid of waste through the circular design of material use, product use and system applications, and this is achieved through the introduction of efficient business models [9,10].

An important detail in describing the models of the circular concept is that it further develops the usable indicators of the previous two ideas—the bioeconomy and the low-carbon economy—to describe biological and technological cycles. In all of his documents, he emphasizes the importance of developing the scientific basis and systemic relationships. Currently, the Ellen MacArthur Foundation's research community publishes the most professional publications on the topic in Europe. However, the majority of European university research teams and scientific research institutes are also interested in the scientific background for the development of the circular economy. The circular concept is the result of a shift from a simple mitigation model to an absolute value creation model that is socially, economically and environmentally positive.

Central to this is the decoupling of economic growth from increasing resource use and reducing adverse environmental impacts. A very important benefit of the decoupling economic approach is that business "sustainability" has become a comprehensive, social and economic necessity among governments, international organizations and businesses alike. Leaders in different sectors now understand that moving towards a more sustainable economy requires a global reduction in resource use, while human well-being requires an increase in economic activity and a local reduction in environmental impacts. The dilemma of expanding economic activities can be solved with this concept by reducing the rate of resource use while also reducing the environmental impacts of resource use [11].

In circular economic theory, unbundling means that we have to use fewer resources per economic emission unit on the input side, and from the resources used, the environmental impacts on the emission side also decrease exponentially [12,13]. The decoupling logic illustrates the two key aspects of decoupling sustainable development well, namely the separation of resources and environmental impacts. According to the resource-impact separation model, changes brought about on the input side result in a more efficient use of existing resources and technological assets and avoid the accumulation of means of production. On the output side of the production process, by recovering energy stored in secondary raw materials, we can reduce pollutant emissions and avoid external effect (harmful external, usually environmental, social costs).

Based on the professional concept established by the Ellen MacArthur Foundation in 2012, three important principles have been identified for the optimal design of circular economic systems [14].

#### *2.1. Principle of Inputs*

The first principle of the circular economic concept is to keep resource resources under control and to balance the material flow of renewable energy sources, to preserve and increase natural resource systems. In the case of inputs, the system is basically used to maintain the flow of renewable energy sources, so-called "flow or flow management", and aims to continuously circulate stocks instead of accumulating them, i.e., to stockpile them, while serving technological processes. Therefore, in terms of economic processes, they also focus on ensuring that renewable materials, resources and non-renewable raw materials are always available. In terms of systems that implement cycles (such as soil regeneration or the provision of secondary raw materials), this is achieved primarily by maintaining the flow of materials, most notably by continuously increasing the proportion of services. Therefore, the operation of the input side of circular economic systems requires, where possible, the provision of energy sources free from political and economic risks (production of renewable energy with local supply) and safe access to secondary raw materials by keeping material flow subsystems [15].

#### *2.2. The Principle of Sustainable Cycles*

The previously mentioned biological and technological cycles or cycle processes close the processes of the subsystems through loops of different lengths. As the functioning of the economy, but especially its growth, depends on the amount of resources available, these cyclical processes are able to ensure that production systems continue to function properly. In linear systems, if the resources (raw materials) essential for production cannot be obtained, the economy will be unable to grow or develop. Circular economic solutions offer directions for development that can ensure that these resources are always available at the highest possible level of material cycles (biological raw materials and raw materials) [14]. Its aim is to release the raw materials of the biological cycle processes into the environment through the shortest possible cycles, so-called cascades (e.g., circulation of soil nutrients, water cycle). The new product cycles of circular economic models are mainly generated in technological cycles, by re-acquiring resources or by modernizing and improving technological systems. It incorporates the requirement for circular design into the early stages of product design in order to reduce energy consumption throughout the product life cycle. Waste-free design principles that can be applied at this level therefore include reuse and recycling planning, remanufacturing, refurbishment, energy efficiency and flexibility of use. The essence of circular operation in sustainable cycles thus lies in the design of the product or service [15].

#### *2.3. Principle of Outputs*

Increasing the efficiency of the system must be achieved by accurately identifying the processes, adhering to the principles of the original circular design and providing the possibility of redesign, through which we can avoid negative and positive externalities with great certainty. This may include planned land use, avoid water and noise pollution, maintain good health, avoid the use and generation of toxic substances, avoid improper business solutions, and perform all of the interventions listed above using local resource utilization systems. In recent years, the principles of circular design have evolved the most in the direction of sustainability. In business innovation, environmental or economic problems are not solved through the development of technological systems or organizational innovation, but through a more efficient allocation and use of existing resources and means of production. As a result, far fewer new devices and equipment are introduced into production, and thus less pollution appears at the system level in connection with the production of these devices [15]. In business innovation, the process of value creation only supports systems that are viable on their own (also financially sustainable) [16]. With this, you can safely avoid harmful government interventions, negative externalities, and most of the external phenomena that were previously indispensable in business solutions referred to as sustainable. The development of closed-loop material flows, which may primarily be the responsibility of the circular service sector in the future, will significantly change the potential outputs of the consumption system. Zero waste systems can become an essential structure for economic systems thanks to proper regulation and the rapid development of a closed-loop material flow service system. This is illustrated, for example, by the announcement by British Prime Minister Boris Johnson in February 2020 of the UK's first post-Brexit climate action [17]: "Like several European countries, the UK has pledged to phase out petrol and diesel sales by 2040. However, the new plan is to bring this date forward five years and to add hybrids to the ban list".

This means that from 2035, only electric vehicles and electric vans will be available on the UK car markets.

#### **3. Business Model Innovation**

Irrespective of the EU Circular Action Programs, the application of linear-circular transformation, transition management, and system models based on feedback from cycles has already started in business [18]. There are economic sectors where this phenomenon is very spectacular (biotechnology, informatics, transport), the linear-circular transformations observed in these areas are actually the result of the natural development of business models. The resizing of business processes and models—that is, circular business model innovation—is therefore, if not necessarily conscious, an integral part of current business processes. In traditional value chains, these innovation processes can diverge, consumer chains break, economic and social change processes run side by side, changes actually evolve side by side (in each sector separately) and there is no relationship between the resources used. In this case, innovation in the traditional sense is not necessarily a useful element of system processes either (disruptive innovation effect). Nevertheless, development does not stop, but without the different levels of development (or values) building on each other, the loss of resources in the transformation process can be very significant, and the development/transformation phases lengthen. That is why it has a key role to play in consciously building the values that we want to see as an integral part of economic life for a long time to come. Sustainable business models are thus well-embedded systems, use resources efficiently and operate with less risk (mainly affecting risk factors stemming from global systems), permanently changing people's lives and the ways companies or society operate in a given circle. This position is in line with [5], who viewed environmental solutions as market expectations rather than complementary functions. The authors argued that the current benefits of business as usual (BAU) processes will soon pose a threat to companies in many ways. These include deficiencies in primary resources, including resource price volatility, declining supply chain efficiency, increasing bans on waste trading, declining costs of renewable energy sources, etc., and these unfavorable patterns can also be termed "linear risks". Recent studies [6,19] supported the above when they argued

that the profitability of "mainstream" economic systems lies in outsourced external factors, i.e., it is cheaper to waste resources than to monitor and eventually regain them. However, this situation seems to be changing soon, as key global players (e.g., China, Kenya, Bangladesh) have exited from the waste markets.

It can therefore be assumed that the transformation from the "take-make-waste" approach and the creation of closed resource loops will be a basic requirement for companies and economic actors in general. This is one of the reasons why the European Commission has issued the Closing the Loop (An EU Action Plan for the Circular Economy) action plan, also mentioned in the introduction, which urges the transition to a circular economy [18]. The Circular Economy Action Plan is a concept that rejects the traditional features of economic growth (e.g., mass production, use of non-renewable resources, production of preserved goods, etc.) but offers innovative solutions to preserve natural capital and enhance social well-being. Achieving the best possible circular flow of materials and energy through economic processes and avoiding resource leaks is a top priority [20]. Contrary to previous sustainability efforts, these circular initiatives are receiving increased attention from the business sector. According to a recent study by the World Business Council for Sustainable Development (WBCSD), 80% of companies surveyed say that accelerating growth and increasing competitiveness depend on the use of circular strategies. The remaining 20% identified risk reduction as the main motivation for developing business models [21]. These results suggest that the application of circular strategies has reached the realm of business model research. In interpreting the concept of circular business models, Scott (2013) [22] argued that circular initiatives should use recyclable biological materials or use their technical raw materials continuously. Both activities are expected to be harmless to ecosystems and can be operated without waste. According to Mentink (2014) [23], circular businesses need to create value and capture material flows in a closed material cycle. However, he pointed out that a business model alone cannot be a circular system. Previous studies have not examined the business-level changes in circular progress, i.e., what circular elements and solutions the currently used business models use, and what phase of the linear-circular transformation they are in. Therefore, the main goal of our research in the future should be to evaluate the current business models and to analyze their fit with circular solutions. In characterizing business models, Segers (2015) [24] highlighted that each model variant is most often used in a consolidated manner by market participants, so a firm integrates the mechanisms of multiple models into one application when looking for the right solution for itself. In order for a small business to develop a proper business model, it must consider important design considerations [25]. One of the most popular types of sustainable business model design methods is the canvas design matrix, developed by Osterwalder and Pigneur (2010) [26] under the name "Business Model Canvas" (BMC), which has gained incredible popularity over the past decade. Lewandowski (2016) [27], who proposed the ReSOLVE criteria system for the circular evaluation of business models, considered BMC itself to be the best tool for developing and customizing business models. In a visual matrix, BMC demonstrates to the stakeholder how their business can create, deliver and capitalize on the value it offers. Of course, designed business models cannot consist of just circular attributes, as the operation of a business requires several additional activities that do not directly affect energy and material flows.

#### **4. Technological Solutions**

The sustainable engineering approach has represented the foundation that can be learned in environmental education, the importance of the three core competencies (reading, writing, arithmetic). Over time, environmentalists—symbolizing the priorities they represent—also created their own 3R trend by the second half of the twentieth century; it refers to the reduction in rapidly increasing amounts of waste (reduce), recycling (recycle), or prevention of their formation at all by reusing products (reuse). Thus, the theory of the circular economy [15], which is gaining more and more ground today, relies on these 200-year-old pillars. The concept was born in response to the linear economic approach that prevailed until the beginning of the 20th century, which favors production based on the use of new

resources and then the disposal of products after their useful lives (end of life). In the cycle of natural ecosystems, the end product created by one life form always serves as a nutrient for another life form. It is inconceivable that any living thing in nature would create an 'output' that would not constitute an 'input' for another organization [28]. Another important aspect of natural life, in addition to the absence of waste generation, is that the phenomenon of overconsumption is also unknown. In the early stages of history, humanity, like animals, had to hunt, collect, and later produce for itself in order to obtain the food it needed. Today, however, these processes have been replaced by artificial care systems. Foods, which are thus becoming cheaper and more readily available, have induced the development of consumption, which is sometimes immoderate today [29]. In the last half century, however, our economy has begun to push for the overuse of people in other areas of life. The camp of representatives of alternative economic trends sees the foundations of today's consumer society in three main pillars. The first of these is the previously planned obsolescence.

The second such aspect is the issue of the use of credit. Although this tool has always been used to stimulate the economy, it was initially used with the aim of having its user invest the money earned in this way for later income. Later, however, it became common to use it to satisfy a constant consumption compulsion. Finally, marketing has emerged as another cornerstone of consumer society as one of the most effective ways of influencing consciousness to stimulate growing consumption. It is important to emphasize the processes that take place in nature, as this also contributes to the correct interpretation of the circular economic concept. This is because, in the light of experience to date, the name 'cycle' often gives rise to misinterpretations. This can be fatal in the sense that the scientific and practical foundations of the concept are still being laid. Based on what has been seen so far, the circular designation has repeatedly diverted researchers' attention towards increasing recycling. That is, most experts started from the question of how to recycle all the waste that humanity produces into production systems. This certainly proves to be a misinterpretation. Circularity actually refers to the environmental cycle as explained above. The idea is that the economy should replicate the functioning of natural ecosystems, where the functioning of systems in symbiosis with each other precludes the appearance of waste from the outset [30].

Furthermore, there is no overconsumption in this cycle. The theory itself cannot be said to be entirely new, as alternative trends (e.g., biomimicry, industrial ecology, natural capitalism, the cradle to cradle principle, the blue economy) have emerged continuously since the 1970s, placing production on systems with a natural basis. The circular economic theory sees all these theories as a breeding ground and its guiding principle is "The problem must be solved at the root!" view. This also emphasizes the need to work to avoid the appearance of waste instead of looking for waste management solutions [31]. The source of this can be seen in a much older context, the Jevons paradox, considered one of the foundations of environmental economics. In his 1865 book 'The Coal Question', William Stanley Jevons explained the long-term negative mechanism by which technological advances are aimed at increasing the efficiency of current systems. According to his example, although improving the efficiency of coal-based production has reduced industrial air pollution in the short term, more economical processes have ultimately led to the increased use of fossil fuel technology and higher CO2 emissions [32]. Based on this, it is easy to imagine what would happen if circular solutions focused solely on recycling material flows back into production. The '3R' guideline presented at the outset is based on a similar logic, with only one of the three keywords focusing on recycling, the other two calling attention to curbing our consumption and maximizing the use of products we have already purchased. This is also based on Tom Szaky, director of the world-famous waste management company Terracycle. According to him, before declaring a product a waste, we need to focus on three things. The first is the function you loaded. If, in our opinion, it has not been used to such an extent that it is unable to fulfill its original purpose, we will continue to use it. In cases when it no longer meets our needs, we offer it to 'second hand' stores where others can still decide if they are willing to use it in its current form. The second important aspect is the shape of the product. In today's world, we have become accustomed to the fact that production systems assign different products to each function in order to increase consumption. As a result,

we often do not even think about how many different purposes an object could be utilized for if we used our creativity. For example, instead of buying new pots, we can put our plants in used sour cream boxes. The series of examples could continue for a long time, as so-called 'further use' is now being built on several business models. Returning to Szaky's line of thought, the material of the worn-out object also appears as the last aspect. If we judge that a product no longer serves its original function for itself or for others and cannot be utilized for other purposes, we can think about recycling [29]. In developing circular theories, researchers use the 'R' -labeled methods presented earlier and follow a philosophy similar to that of Tom Szaky. The repository of waste management and prevention practices has now been expanded to '10R', which have been considered as priority levels in the circularity (refuse/reduce/renew/reuse/repair/refurbish/remanufacture/recycling/re-purpose/recovery).

In the circular concept, two priority aspects can be identified, along which we reinterpreted the order of methods and technological solutions. The application of the 'function before substance' principle aims to maintain the original purpose of the product for as long as possible. This ensures that the product used in the preferred function uses the least amount of material. The second priority is to minimize the energy used. That is, after the end of the useful life, convert the products for later use to use as little energy as possible.

#### **5. Outlook and Conclusions**

Further research is needed to clarify the theoretical details of the circular economy. A complete overview of resource systems needs to be set as a goal in order to extend the potential business innovations to the use of free resource elements with the greatest efficiency. A key goal in the future is for circular business models to focus not only on energy or material transport processes in scientific research, but also on the use of human resources or the circular operation of financial resources as a part of research. In order to eliminate existing or ongoing externalities for the sustainable operation of business models, it is necessary to know exactly which elements can be considered as the interventions needed to implement the circular economy, which are the parts and which are not. Linear-circular transformation processes are micro-, meso- and macro-level processes, the coordination, management and acceleration of which require information and data that can only be collected coherently from public and private data collection systems. In linear systems or in the traditional value chain, sectoral development processes may deviate from each other, there are no values, the processes of economic and social change do not or rarely meet each other, innovation processes do not support each other in the use of resources, but compete for available resources. Then, innovation is not a useful element of system processes either. Nevertheless, development does not stop, but without the different levels of development (or values) building on each other, the loss of resources in the transformation process can be very significant, and the development/transformation phases lengthen.

In circular business innovation, environmental or resource problems are not solved through the development of technological systems or organizational innovation, but through a service-based, more efficient allocation of existing resources and means of production. The presence of circular business solutions in the environmental sector is currently not common, because the tax system following the polluter pays principle in Pigou cannot deprive the state of its prominent role in the operation of the processes. Modification of this system property is essential to motivate circular mechanisms.

**Author Contributions:** During the work, C.F and D.F. were responsible for the conceptualization of the scientific content. D.F. contributed to the review of the literature. Then, C.F. wrote the article with the supervision of D.F. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** Thanks to Prespa Ymeri for her support in the editing work.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## *Article* **Life Cycle Assessment of the Closed-Loop Recycling of Used Disposable Diapers**

**Norihiro Itsubo 1, Mitsuhiro Wada 2, Shigeo Imai 2, Akira Myoga 2, Naoki Makino 3,\* and Koichi Shobatake <sup>3</sup>**


Received: 31 January 2020; Accepted: 12 March 2020; Published: 17 March 2020

**Abstract:** In Japan, approximately 23.5 billion paper diapers are produced annually (total of diapers for infants and adults produced in 2018). The majority of used paper diapers are disposed of through incineration; in certain regions, some paper diapers are recycled, mostly by open-loop recycling or thermal recycling. To date, several methods of recycling used paper diapers have been proposed and developed, but these methods are considered to have different types and amounts of recycled materials and different environmental performances. In this study, a new technology was developed for the closed-loop recycling of used paper diapers, and the use of the recycled pulp and superabsorbent polymer (SAP) as materials for paper diapers was evaluated via the environmental impact using the life cycle assessment (LCA) method, using data obtained from experimental facilities for recycling. The results between the comparison of the new method with the landfill and incineration processes demonstrate a greenhouse gas reduction of 47% and 39%, respectively. The results also show that such recycling is expected to reduce land-use occupation and water consumption, closely related to the pulp, main raw material of paper diapers.

**Keywords:** disposable paper diaper; material recycling; closed-loop recycling; life cycle assessment (LCA)

#### **1. Introduction**

Paper diapers are roughly divided into two types: those for infants and those for adults. Paper diapers for infants, which are highly convenient as they do not require laundering like cloth diapers, are essential for daily life in Japan. Paper diapers for adults have also become indispensable, given the increasing number of persons requiring nursing care and the shortage of caregivers, in line with the progressive aging of society. In 2018, in Japan, the annual production of paper diapers for infants was approximately 15.1 billion, equal to 480,000 tonnes, while that of diapers for adults mainly used in nursing care facilities and medical institutions stood at about 8.4 billion, equal to about 390,000 tonnes [1]. The production volume has been increasing for 10 years, since 2010: 1.7 times for diapers for adults and 1.9 times for those for infants. Paper diapers for adults, in particular, are expected to further increase in the future, due to the rise in the elderly population [2].

Paper diapers consist of pulp or superabsorbent polymer (SAP) used as a moisture absorber, exterior materials, waterproof materials, and plastic materials such as polyethylene or polypropylene used in internal nonwoven fabric material. Pulp, which accounts for the majority of the materials, is made of virgin materials for needle bleached kraft pulp (NBKP, or nadelholz bleached kraft pulp

in German). The annual consumption of materials for NBKP, SAP, and plastics is estimated at approximately 330,000, 230,000, and 250,000 tonnes, respectively, based on the annual production [1] and the material composition of paper diapers (study by Unicharm Corp.).

The majority of used paper diapers from general households are collected and incinerated by local governments as combustible waste in the category of domestic general waste [3]. Paper diapers are considered to cover 6%–7% of the total volume of household combustible waste, and the high moisture content due to excreta included in used paper diapers leads to a low calorific value, inhibiting heat recovery efficiency during combustion [4]. Used paper diapers from business operators such as nursing care facilities and hospitals are not collected by local governments in principle but instead are entrusted to special disposal companies who collect and incinerate them as general waste from business activities or specially controlled waste [5].

As such, used paper diapers are mostly incinerated in Japan, but there are also some efforts and study cases on the recycling of paper diapers. Fujiyama et al. [6] conducted an analysis and a comparison with incineration processing of the material recycling of recovered recycled pulp to be used for fireproof plates, in addition to the manufacture of refuse paper and plastic fuel (RPF) from the thermal recycling of used paper diapers. They reported that greenhouse gas (GHG) emissions from recycling can be reduced by about 37% compared with incineration. A study related to the recycling of water absorptive sanitary products [7,8] also discussed thermal recycling treatment systems for processing used paper diapers recovered as they are, without separating or cleaning them, for conversion into solid fuel. Quantification of environmental loads adopting the life cycle assessment (LCA) is not confirmed, but reference was made to the possibility of reducing CO2 emissions by using them as boiler fuel instead of fossil fuel. In the recycling of used paper diapers targeted for studies reported by Itsubo et al. [9], the preceding report of this paper revealed that recycled pulp has the same quality as NBKP, the virgin material that is the main component of paper diapers, which shows that pulp can be closed-loop recycled. It is also indicated that GHG emissions can be reduced by about 26% compared with incineration, as well as significant reductions in water consumption and land use occupation, areas where the pulp is considered to have high potential effects.

The present study introduces a new recycling technology that achieves the closed-loop recycling of SAP. This new recycling technology adopts a new crushing/cleaning/separating technology and improves the recycling rate for pulp, etc., and recycles SAP to the same quality as virgin materials, where SAP was thermally recycled with the preceding recycling technology. The environmental load over the entire life cycle of paper diapers from the acquisition of raw materials to the disposal/recycling phases is quantified.

There have been several reports on the recycling of used disposable diapers overseas [7,10–13]. An LCA report [12], which collected data from an experimental-scale recycling plant, stated that plastics could be recycled and pulp containing SAP could be used to generate the steam needed for the sterilization process, which indicates that the environmental impact is reduced compared to landfill disposal.

Many previous studies have focused on climate change. Disposable diapers use paper as the main material, and the supply of chips, the main raw material for paper, requires a lot of land use and water consumption. Recycling of disposable diapers is expected to contribute to reducing the burden on water consumption and land use but has not been evaluated in previous studies. In this study, in addition to climate change, water consumption and land use are evaluated.

#### **2. Materials and Methods**

#### *2.1. Objective*

This study assesses the life cycle of paper diapers, including the closed-loop recycling that recycles pulp and SAP from used paper diapers into a quality product to be used as the raw material for paper diapers. The quantified environmental impacts are discussed and compared with those for incineration and landfill. In performing the LCA, an inventory analysis and impact assessment were conducted for the production, transportation, recovery, recycling, and disposal of disposable diapers in accordance with the international standard for ISO 14040 [14].

#### *2.2. Scope of This Study*

#### 2.2.1. Overview of Key New Technologies for Closed-Loop Recycling

#### 1. Crushing, Washing, and Separation Technologies

Used paper diapers are required to be degraded into composition materials such as pulp, SAP, and plastics for recycling. The crushing process is characterized by dissolving the diapers in an organic acid solution of pH 2.5 or less, which prevents a reduction in treatment efficiency as there is no loss of liquidity in the treatment tank caused by the swollen highly water absorptive polymer [15]. It also has the effect of continuously securing hygiene in the facility, using a safe organic acid to enable safe treatment and to prevent odor and contamination. In conventional techniques using a water solution for the basic cleaning/separating process [9], SAP absorbs a large amount of moisture to become gel-like, losing its liquidity. This, in turn, greatly reduces the performance of the treatment equipment, making it necessary to use a large amount of lime to inactivate the SAP. Moreover, the use of hypochlorite as a disinfectant generates a highly alkaline environment in the treatment tank, which degrades the pulp fibers and lowers the pulp recovery rate and quality. Conventional techniques also require lengthy agitation and heating for separation, making it difficult to improve treatment efficiency. The process in this study, that is, applying the new technology, improved the recycling rate of SAP to about 80% and that of pulp also to about 80% compared to around 40% with conventional techniques [9].

#### 2. Ozone Treatment Technology

Reusing the pulp recovered from the crushing/cleaning/separating process as raw materials for paper diapers requires that the pulp be recycled to a sufficient quality usable for sanitary materials. Ozone treatment uses ozone water to dissolve and solubilize SAP contained in the recovered pulp as residue, then discharges the ozone water to remove the SAP from the pulp, thereby extracting pulp ingredients only [16]. Ozone treatment also thoroughly sterilizes the pulp, eliminating the need for disinfectant. Moreover, ozone is returned to oxygen after use, without generating resistant bacteria, which improves the safety of recycled pulp.

#### 3. SAP Reactivation Technology

As the SAP recovered from the crushing/cleaning/separating process is inactivated, it is necessary to recover the water absorption performance so that it can be used instead of virgin SAP [17]. Conventional techniques [9] use acid or alkaline treatment, which leaves the possibility of acid or alkaline residue in recycled SAP if not completely neutralized. Using such recycled SAP as raw materials for paper diapers may cause skin irritation, making it difficult to reuse as sanitary materials. However, the process targeted in this study makes it possible to recover the water absorption performance of SAP by neutralizing the SAP that has been inactivated by the organic acid solution.

#### 4. Verification of the Quality and Safety of Recycled Products

The present study targeted closed-loop recycling, where pulp and SAP are recycled to a quality equal to that of virgin materials, and thus are usable as raw materials for paper diapers. The quality of the pulp was confirmed by consigning inspections about the standards stipulated by the Ministry of Health, Labour, and Welfare (MHLW) [18] to a third-party inspection organization. Inspection items and results are summarized in Table 1. The recycled SAP was also confirmed to have a water absorption performance equal to that of SAP in virgin materials, and thus can be used as raw materials for paper diapers.



#### 2.2.2. Functional Unit

The functional unit is assumed as the "provision of one paper diaper and its disposal." Paper diapers have different material compositions and composition ratios depending on the manufacturer and the shape. The individual material composition ratios for paper diapers for adults and infants (study by Unicharm Corp.) were calculated by weighing them with the individual production volumes [1] to determine the average material composition ratio (see Table 2). In this study, 40.5 g per paper diaper was adopted for the average weight of all paper diapers, including those for adults (except underwear liners or pads), based on diaper production statistics (2019) [1] (see Table 3). Furthermore, the composition of excreta included in used paper diapers is based on studies by Unicharm Corp. and literature values [19] (see Table 4).

**Table 2.** Material composition ratio of paper diapers. SAP, superabsorbent polymer.




**Table 4.** Composition of 1 tonne of used paper diapers.


#### 2.2.3. System Boundary

The scope from the acquisition of raw materials to the production, distribution, and disposal/recycling of paper diapers was selected as the system boundary. For the use phase, non-use of electric power, fuel, and other utilities were assumed, thus these processes were excluded from the scope of the assessment. Figure 1 illustrates the life cycle flow. As comparable systems, two models using incineration and landfill to treat waste in the disposal/recycling phase were set. For incineration, the combustible general domestic waste treatment currently used in Japan was assumed. For waste power generation, the power generated was assumed to substitute the average purchased power in Japan. For landfill, general waste landfilling was assumed. In this paper, the systems for recycling, landfilling, and incinerating waste in the disposal/recycling phase are called RE, LF, and IN, respectively (see Table 5). Table 6 shows the recycled products and alternative products.

**Figure 1.** Life cycle flow chart. The upper part shows the life cycle of paper diapers, and the lower part shows details of recycling, waste treatment scenarios. The system boundary is from raw material production, disposable diaper production, transportation, disposal/recycling, production of recycled products, and production of alternative products (excluding storage, sales and use of disposable diapers). RE, recycling; LF, landfill; IN, incineration; RPF, refuse paper and plastic fuel; NBKP, needle bleached kraft pulp.




#### 2.2.4. Impact Categories

Table 7 shows the impact categories and evaluation methods for the targets. In addition to global warming, land use occupation (maintaining) and water consumption were also included as impact categories closely related to pulp, the main raw material of paper diapers. Furthermore, blue water was considered as the target for water consumption.



#### *2.3. Inventory Analysis*

#### 2.3.1. Data Collection

#### 1. Raw materials acquisition stage

The input amount of each raw material was determined by multiplying the average material composition ratio for paper diapers for adults and for infants, calculated from their respective composition ratios, by the average weight of paper diapers (see Table 8). For transport, the scenario of importing NBKP from North America via marine transport, and procuring other materials in Japan via land transport using trucks (see Table 9), was used.

#### 2. Production stage

For energy input related to paper diaper production, primary data were collected from the paper diaper plants of Unicharm Corp. Raw material residue generated in the production processes was used as raw materials for pet goods and other products within the same plant; thus, it was assumed that no material loss occurs (see Table 8).


#### **Table 8.** Main collected data and collection methods.

**Table 9.** Transport scenarios.


#### 3. Distribution stage

Paper diapers are generally distributed from the manufacturers to the stores, nursing care facilities, etc., through many distribution channels, which makes it difficult to determine the actual distribution amounts and distribution routes in detail. Therefore, in this study, it was assumed that the diapers are distributed from the paper diaper plants of Unicharm Corp to all 47 prefectures nationwide, with the distribution amounts proportional to the population of individual prefectures. The transport distances for individual prefectures were determined using Google Maps and were then weighed by the transport amount for individual prefectures. For the vehicle class and loading ratio, general domestic transport was assumed (see Table 9).

#### 4. Use stage

In this stage, no additional energy was used, so it was excluded from the assessment of environmental impact.

#### 5. Recycling, waste treatment stage

For RE or recycling processing, primary data were collected from simulated demonstration experiments at a recycling plant being developed by Unicharm Corp. in Shibushi City, Kagoshima Prefecture that processes about 500 tonnes of waste annually (see Table 8). Eighty percent of the SAP and pulp included in the used paper diapers is recycled, and part of the unrecycled content is mixed with plastics to produce RPF. The plastics are completely recovered and then mixed with part of the unseparated pulp and SAP to produce RPF. For LF and IN, it was assumed that one tonne of used paper diapers with the same composition as in RE is processed. Since waste is separately recovered in a polyethylene collection bag of 20 g per 5 kg of used paper diapers in RE, it was assumed that the same bags are used in LF and IN and that the scenarios for transport related to waste materials and collection are common to RE, LF, and IN (see Table 9).

#### 2.3.2. Background Data and Software

Background data from the Life Cycle Inventory (LCI) database IDEAv2 [21] were mainly used, with missing data complemented by the GHG Emissions Accounting and Reporting Manual [22], and SimaPro 8.5 was used for the calculation.

#### **3. Results**

#### *3.1. LCA Results and Comparison between the Three Scenarios*

The LCA results of the system targeted in this study, which assumes the disposal/recycling phase as "recycling processing" in the life cycle, as well as the results for landfill and incineration are shown in Figure 2 and Table 10. The system boundary is the life cycle, including the individual phases from the acquisition of raw materials to the production, use, and disposal/recycling of paper diapers, and the functional unit is the provision of one paper diaper (40.5 g).

**Figure 2.** Life cycle assessment (LCA) results and comparison between the three scenarios.


**Table 10.** LCA results for each scenario and reduction effect rate.

#### 3.1.1. Global Warming

GHG emissions of IN and LF were calculated as 162 and 187 g-CO2e, respectively, while that of RE was estimated at 99 g-CO2e, a reduction of 39% and 47% compared with IN and LF, respectively. In RE, the amount in the disposal/recycling phase was 100 g-CO2e, larger by 11%–45% compared with IN and LF. However, a significant reduction effect compared with IN and LF is expected in the entire life cycle, with the contribution of the total deduction at 97 g-CO2e due to the substitution effect of recycled pulp, SAP, and RPF.

#### 3.1.2. Land Use Occupation

The land use occupation values for IN and LF were almost the same at 474 cm2a, while that for RE was estimated at 139 cm2a, a reduction of 71% compared with IN and LF. About 99% of the loads from IN or LF are due to pulp production included in the raw materials acquisition phase, while RE has a lower value in this phase due to the substitution effect of recycled pulp. Thus, for RE, the load is expected to be reduced in the life cycle.

#### 3.1.3. Water Consumption

Water consumption values for IN and LF were calculated at 0.453 and 0.446 L, respectively, about 97% of which is the contribution from the raw materials acquisition phase, and about 75% in this phase is the contribution from pulp production and SAP production. The value for RE was 0.354 L, although the ratio in the disposal/recycling phase for RE was 0.19 L, accounting for 53% of the total compared to 2%–3% for IN and LF, due to the contribution of 0.069 L of cleaning water and 0.10 L related to the production of organic acid for cleaning chemicals. Meanwhile, the value for RE in the entire life cycle was estimated to be 21% and 22% lower than that for IN and LF, respectively, with the contribution from the substitution effects of recycled pulp and SAP.

#### *3.2. Detailed LCA Results at Recycling, Waste Treatment Stage of the Recycling Model*

The treatment scenarios targeted in this study are characterized by recycling in the disposal/recycling phase, so the LCA results for disposal/recycling, ranging from collection/transport to production of the recycled products and using the substitution effect (deduction) with the recycled products as the system boundary, are presented in detail (see Table 11). The process IDs in the table correspond to the symbols in (a) to (m) described in the individual processes in Figure 1. The functional unit was the disposal/recycling of one used paper diaper.

#### 3.2.1. Global Warming

GHG emissions were calculated at 3.18 g-CO2e. Emissions related to the phases from the collection/transport of used paper diapers to the production of recycled products were 100 g-CO2e (subtotal-1), due to a significant contribution of 97.2 g-CO2e (subtotal-2) from the deduction total as a result of NBKP production (j), SAP production (k), as well as thermal coal production and combustion (l), (m), substituted by recycled pulp, SAP, and RPF. Details of the recycling are as follows: 7.8% for collection/transport (a); 22.7% for crushing/cleaning/separating (b, c, d, e); and 69.5% for recycled products production (f, g, h, i). The substitution effects for NBKP production and SAP production were 19.3% and 20.2%, respectively, while that for thermal coal production/combustion was the highest at 60.4%, due to a significant contribution from CO2 direct emissions caused by combustion.


**Table 11.** Detailed life cycle assessment (LCA) results at the recycling, waste treatment stage.

#### 3.2.2. Land Use Occupation

The land use occupation was <sup>−</sup>333 cm2a, considered as a negative load in the entire process, due to the contribution from the deduction by the substitution effect. Details are as follows: the total of the recycling, from collection/transport to recycled products production (subtotal-1), was 42.2 cm2a; and the total of the deduction from the substitution effect by recycled products (subtotal-2) was 376 cm2a. In recycling, the crushing/cleaning/separating phase (b) accounted for the majority at about 94%, which was largely due to the contribution from land use in the plant culturing phase, as the organic acid used was plant-based. Meanwhile, the substitution effect of NBKP production (j) was 375 cm2a, accounting for almost 100% of the total at 376 cm2a, which was due to the significant contribution from land use related to the production of forest resources (softwood) used as materials for virgin pulp, which was avoided by using recycled pulp.

#### 3.2.3. Water Consumption

The water consumption per paper diaper was −0.0886 L as a whole, a negative value calculated by deducting the substitution effect. Details are as follows: the total of the recycling, from collection/ transport to recycled products production (subtotal-1), was 0.192 L; and the total of the deduction from the substitution effect of recycled products (subtotal-2) was 0.281 L. In recycling, the crushing/cleaning/separating phase (b) accounted for the majority at about 94.5%, among which about 40% was due to directly consumed water in the cleaning tank, while about 60% was due to production of the plant-based cleaning agent.

#### **4. Discussion**

#### *4.1. Comparison with Previous Studies*

The results of previous studies related to the recycling of used paper diapers were reviewed and compared with this study. As previous studies assess only the disposal/recycling phase in the life cycle of paper diapers, the disposal/recycling process from the results of this study were extracted and the system boundary was set to cover "disposal/recycling of one tonne of used paper diapers" only (see Table 12).



Among the domestic studies, Itsubo et al. [9] discuss closed-loop recycling. The paper targeted the closed-loop recycling of recycling pulp as fine pulp usable as raw materials for paper diapers, where plastics and SAP were converted to RPF for thermal recycling. Compared with the present study, this system as characterized by a lower pulp recycling amount by about 30%, but a higher RPF recycling amount of about two-fold. The calorific value for RPF as lower by about 34%, making the total of the substitution effect (deduction) smaller by about 10%. The total GHG emissions related to recycling was about 1.3 times that of the present study, which resulted in a total—including the deduction—at 366 kg-CO2e, which was about 12 times the value in this study at 30 kg-CO2e. Compared with the study by Itsubo et al., GHG emissions related to recycling in this study were reduced by 23%, while the recycling ratio of pulp was about 80%. For RPF, the contamination rate of pulp and SAP residues other than plastics was low, resulting in a higher calorific value, and the deduction was higher due to SAP recycling, significantly reducing GHG emissions as a whole.

In the study by Fujiyama et al. [6], the GHG emissions related to recycling were about 60% of the value obtained in the present study, but the substitution effect (deduction) in their study was about a quarter of the value obtained in the present study at 240 kg-CO2e. This is presumably caused by a lower deduction range per unit of weight of recycled products compared to the present study as Fujiyama et al. used downgrade recycling.

The study report on the processing equipment for thermal recycling of used paper diapers as solid fuel [7] indicates the possible reduction of CO2 emissions by using such fuel as a substitute for fossil fuel, but that effect was excluded from the comparison as the effect was not quantified.

Note that the values in the present study cannot be directly compared with those in previous studies as the prerequisites differ in the following points.


#### *4.2. Estimation of the Potential for Environmental Load Reduction*

The potential for environmental load reduction by recycling used paper diapers in Japan and the world was estimated from reduction amounts obtained in this study and by applying them to the incineration and landfill baselines of Japan and the world (see Table 13). The annual production volume of paper diapers for adults and infants in Japan was 878,000 tonnes. The waste weight was estimated at 2.294 million tonnes, assuming that the disposal weight increase factor was 2.6; this is due to the increased weight from excretion. Based on this waste amount and the ratio of 98:2 for incineration vs. landfill, the reduction potential nationwide was estimated at about 1.314 million t-CO2e for GHG emissions, 726 km2a for land use occupation, and 2.149 million m3 for water consumption.



Overseas, the annual production volume of paper diapers was estimated at 120 billion [23], but the weight per diaper is unknown. Thus, the production volume for the world was estimated at 4.866 million using the average weight of 40.5 g for diapers for adults and infants produced in Japan. The weight increase factor for disposal was set at the same value as in Japan, or 2.6, and the waste weight was estimated at 12.720 million tonnes. The ratios of the processing methods were set at 63% for landfill and 37% for incineration [24]. Using these prerequisites, it was estimated that the GHG emissions reduction potential was 9.143 million tonnes-CO2e, land use occupation was 4027 km2a, and water consumption was 12.221 million m3 when applying recycling throughout the world (see Table 13).

The estimates were based on the assumption that all used paper diapers produced in Japan and the world are recycled, which requires the following cautions.


#### **5. Conclusions**

As the production of paper diapers is expected to increase in the future, there is a strong need for an appropriate recycling technology in terms of waste treatment after use and for sustainable use of resources. While previous studies and cases are limited to open-loop recycling, the present study achieved closed-loop recycling of pulp and SAP from "paper diapers to paper diapers" thanks to a new technology, thus clarifying that the environmental load can be further reduced compared to that in the preceding report [9] in the assessment of GHG emissions, water consumption, and land use occupation for the life cycle of recycling used paper diapers (see Table 14). The recycling technology in this study demonstrated a high recycling effect by enabling the recycling of high-quality pulp and SAP. In the future, further reductions in environmental impact are expected through the efficiency of SAP regeneration and the improvement of the recycling rate. On the other hand, in this study, it was considered that uncertainties were included from the following points, but even if these factors are taken into consideration, a significant reduction in environmental load was confirmed.


**Table 14.** Reduction of environmental load by the recycling technology of this study and other recycling technologies.

\* Full life cycle includes all life cycle stages of the paper diaper, from the acquisition of the raw materials to the recycling, waste treatment stage, except for the use stage.

The recycling facility from which the data were collected is a prototype, so its representativeness may be low.


In addition, it is expected that the recycling process of this study will have great social and economic benefits. Analyses focused on social and economic aspects were also assumed, but were not included in this study due to the difficulty in obtaining data, etc., and the immature evaluation method.

**Author Contributions:** Conceptualization, N.I., M.W., and K.S.; methodology, N.I., N.M., and K.S.; validation, N.I., N.M., and K.S.; formal analysis, A.M. and N.M.; investigation, M.W., S.I., and A.M.; resources, M.W., S.I., and A.M.; writing—original draft preparation, N.M.; writing—review and editing, N.M.; supervision, M.W.; project administration, M.W. All authors read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflicts of interest.

#### **References**


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