Sustainability of phosphorus supply chain : circular economy approach

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SUSTAINABILITY OF PHOSPHORUS SUPPLY CHAIN - CIRCULAR ECONOMY APPROACHMohammad El Wali

SUSTAINABILITY OF PHOSPHORUS SUPPLY CHAIN - CIRCULAR ECONOMY APPROACH

Mohammad El Wali

ACTA UNIVERSITATIS LAPPEENRANTAENSIS 977

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Mohammad El Wali

SUSTAINABILITY OF PHOSPHORUS SUPPLY CHAIN - CIRCULAR ECONOMY APPROACH

Acta Universitatis Lappeenrantaensis 977

Dissertation for the degree of Doctor of Science (Technology) to be presented with due permission for public examination and criticism in the Auditorium 1316 at Lappeenranta-Lahti University of Technology LUT, Lappeenranta, Finland on the 22^ndof October 2021, at noon.

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LUT School of Engineering Science

Lappeenranta-Lahti University of Technology LUT Finland

Dr. Saeed Rahimpour Golroudbary LUT School of Engineering Science

Lappeenranta-Lahti University of Technology LUT Finland

Reviewers Professor Ana Paula Barbosa-Povoa

Department of Engineering and Management Instituto Superior Técnico

Portugal

Professor Michael Charalambous Georgiadis Department of Chemical Engineering University of Thessaloniki

Greece

Opponent Professor Michael Charalambous Georgiadis Department of Chemical Engineering University of Thessaloniki

Greece

ISBN 978-952-335-704-4 ISBN 978-952-335-705-1 (PDF)

ISSN-L 1456-4491 ISSN 1456-4491

Lappeenranta-Lahti University of Technology LUT LUT University Press 2021

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Abstract

Mohammad El Wali

Sustainability of phosphorus supply chain – circular economy approach Lappeenranta 2021

75 pages

Acta Universitatis Lappeenrantaensis 977

Diss. Lappeenranta-Lahti University of Technology LUT

ISBN 978-952-335-704-4, ISBN 978-952-335-705-1 (PDF), ISSN-L 1456-4491, ISSN 1456-4491

Access to non-renewable natural resources is becoming more difficult and expensive. It is due to the growing demand triggered by industrial and agricultural development. That is the reason why several research studies have shed light on the circular economy as an approach helping to ensure sustainability and minimize the criticality linked to the use of many raw materials. One of the materials playing a pivotal role in enabling the growth of agricultural production is phosphorus (P). It originates from non-renewable natural resources and is subject to supply risk due to the unequal geological distribution of its natural resources. Countries poorly equipped with its resources are becoming more vulnerable to changes in phosphorus availability and price indices. Therefore, the significance of phosphorus criticality is pushing for efforts to achieve a steady supply of phosphorus and conserve the material value.

While phosphorus conservation is the main objective of the circular economy, previous studies lack the assessment of circularity transitions in the phosphorus chain to tackle the environmental and social challenges. Also, in regions such as the European Union (EU), high reliance on imports still exists despite the availability of secondary phosphorus.

These aspects contribute to the complexity of the phosphorus circular economy.

Assessment of the environmental and social consequences of the phosphorus circular economy is needed to raise awareness of both benefits and costs associated with the circularity transitions. This research aims to analyse the sustainability of the phosphorus supply chain in the circular economy approach. This dissertation presents the dynamics model of the phosphorus supply chain. The model includes the environmental and social sub-systems necessary to assess phosphorus circularity and its impact on the environment and society.

The main findings reflect the complexities involved in the phosphorus circular economy.

Results show that phosphorus circularity can reduce the reliance on imports by providing secondary phosphorus. Environmentally, it exacerbates the GHG emissions and energy consumption. Socially, phosphorus circularity can help to achieve several social targets.

However, it demonstrates a paradoxical behaviour towards the social issues raised regionally. These burdens associated with the transition to phosphorus circularity model justify decisions that on the face of it appear irrational taken by regions using imported phosphorus instead of recycling it.

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dynamics, Bayesian game theory

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Acknowledgements

I would like to thank my supervisor Professor Andrzej Kraslawski who has always been supportive throughout all stages of my PhD. dissertation process. Professor Kraslawski responded promptly to all my questions and was always ready to offer his help and experience while I was working on this dissertation. His comments, supervision, and guidance helped me to develop my research and academic skills.

I would also like to thank my second supervisor Dr. Saeed Rahimpour Golroudbary. Dr.

Rahimpour played an important role in my PhD journey and my research work. He was always generous in providing his help, skills and experience that contributed to the publications I have to date.

I would like thank the reviewers of my dissertation, Professor Ana Paula Barbosa-Povoa, Instituto Superior Técnico, and Professor Michael Charalambous Georgiadis, University of Thessaloniki.

Last but not least, special thanks to the doctoral office at LUT, which has always been supportive and responsive to all my questions and queries regarding my doctoral journey from the beginning till the end.

Mohammad El Wali September 2021 Lappeenranta, Finland

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List of publications

I. El Wali, M., Golroudbary, S.R. and Kraslawski, A., 2019. Impact of recycling improvement on the life cycle of phosphorus. Chinese Journal of Chemical Engineering, 27(5), pp.1219-1229.

II. Golroudbary, S.R., El Wali, M. and Kraslawski, A., 2019. Environmental sustainability of phosphorus recycling from wastewater, manure and solid wastes. Science of The Total Environment, 672, pp.515-524.

III. El Wali, M., Golroudbary, S.R. and Kraslawski, A., 2021. Circular economy for phosphorus supply chain and its impact on social sustainable

development goals. Science of The Total Environment, 777, p.146060.

IV. Golroudbary, S.R., El Wali, M. and Kraslawski, A., 2020. Rationality of using phosphorus primary and secondary sources in circular economy:

Game-theory-based analysis. Environmental Science & Policy, 106, pp.166- 176.

Author's contribution

Mohammad El Wali is the principal author in papers I and III, co-author in papers II and IV, and the corresponding author in paper III.

In paper I, Mohammad El Wali was responsible for conceptualization, data collection, literature, modelling and writing original draft and review. Saeed Rahimpour Golroudbary was responsible for the conceptualization of the idea, methodology, analysis, data collection, writing – preparation, review, and editing of the original draft.

Andrzej Kraslawski was involved in and supervised the conceptualizations of the idea and was involved in writing the review and draft editing.

In paper II, Saeed Rahimpour Golroudbary was responsible for the conceptualization of the idea, methodology, software, modelling, formal analysis, data collection, writing – preparation, review, and editing of the original draft. Mohammad El Wali was responsible for methodology, software, modelling, formal analysis, data collection, writing – preparation and editing of the original draft. Andrzej Kraslawski was involved in and supervised the conceptualization of the idea and was involved in writing the review and draft editing.

In paper III, Mohammad El Wali was responsible for the conceptualization of the idea, methodology, data curation, software, formal analysis, writing – editing and preparation of the original draft. Saeed Rahimpour Golroudbary was responsible for the conceptualization of the idea, methodology, formal analysis, writing – review and editing.

Andrzej Kraslawski supervised and was involved in the conceptualization of the idea and in writing the review, as well as draft editing.

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In paper IV, Saeed Rahimpour Golroudbary was responsible for the conceptualization of the idea, methodology, data curation, formal analysis, as well as preparation and editing of the original draft. Mohammad El Wali was responsible for the conceptualization of the idea, data collection, as well as writing, editing and review. Andrzej Kraslawski was involved in and supervised the conceptualization of the idea and was involved in writing the review and draft editing.

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Nomenclature

CRM Critical raw materials

P Phosphorus

PR Phosphate rock

P4 White phosphorus

GHG Greenhouse gas

USGS United States Geological Survey UN United Nations

UNEP United Nations Environmental Program

EU European Union

SDG Sustainable development goals STTP Sodium tripolyphosphates CO2 Carbon dioxide

CH4 Methane

N2O Nitrous oxide

WWTP Wastewater treatment plants

SD System Dynamics

SLCA Social life cycle assessment FAO Food and Agriculture Organization

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1 Introduction

1.1

Background

Phosphorus is a chemical element that cannot be found as a free element on Earth. It is a material playing a prominent role for all humankind and is essential to life. It has no material substitutes. Phosphorus is found nearly everywhere. Together with nitrogen and potassium, phosphorus is one of the three major contributors to the food and agriculture chain (Cordell et al., 2009). The issue of phosphorus has come under the spotlight after the evolution of our modern agriculture in the 1940s, when concerns emerged as to its cycles and the flow chain (Falkowski et al., 2000). The continuous growth of global population, as well as intensified livestock production and consumption appear to cause problems in securing long-term sustainable flows of phosphorus (Elser, 2012).

Historically, phosphorus has been the central focus of several research studies and conclusions about its nature, demand, biological significance, and reserves were all discussed in the literature. It is an element vital for our daily food and, thus, to our health and livelihood (STEEN, 1998). Demand for it is largely related to food production, as almost 90% of global phosphorus goes to the food sector (Smil, 2000). Its supply has always been subject to global geopolitical influence (Rosmarin, 2004). Within the last decade, research has focused on its prominent role to all living creatures (Lwin et al., 2017), its sustainability challenge in the long term (Childers et al., 2011; van Dijk et al., 2016), the criticality level of phosphorus (Scholz and Wellmer, 2013), its potential scarcity (George et al., 2016), its importance for nutrition (Cordell and Neset, 2014), and its environmental impact on society (Daneshgar et al., 2018; Rowe et al., 2016).

The major source of phosphorus, phosphate rock, is a non-renewable natural resource.

Historically, global attention was not focused on the sustainable use of phosphorus as a material whose natural resources are finite. Currently, this view is gradually being shifted to address the resource scarcity and the availability of the material for current and future generations. Despite the non-renewable nature of its primary resource, phosphate rock, the issue of phosphorus scarcity is not yet fully proven (Wellmer and Scholz, 2017).

However, the unequal geographical distribution of phosphate rock globally leaves many regions with no or very few substantial reserves of phosphorus (van Dijk et al., 2016).

Around 88% of total phosphate rock reserves are found in a handful of countries including Morocco and the Western Sahara, China, Algeria, Syria, Russia, and South Africa (Chen and Graedel, 2016). As a result, many regions are left with the only option of relying on foreign exporters. This reliance is also influenced by the geopolitical circumstances around the world. It puts these regions under the risk of supply disruptions of phosphorus and the challenge of ensuring food security to societies. Potential regional scarcity and growing demand for phosphorus have made it a critical material, which was confirmed by findings of several studies and opinions of many institutes.

The definition of criticality still awaits the consensus of the scientific community. One may come across different definitions in various regions. Critical material definition can

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be based on the function (National research council, 2008), supply risk (Blengini et al., 2017; GPO, 1979), demand (EU Commission, 2010; Price, 2011), vulnerability, economic importance, energy (Price, 2011), and environmental risk (EU Commission, 2010). One of the earliest definitions of a critical material states that for a material to be critical, it (a) should be needed to fulfil industrial and societal needs of a region and (b) is not found, not available or not produced within this region (GPO, 1979). The assessment of criticality of materials varies across geographic regions. However, supply risk is considered to be one of factors typically included in the assessment methodology (Jin et al., 2016). Phosphorus is a candidate for a critical material for the European Commission as it complies with supply risk and economic importance criteria in the criticality assessment (EU Commission, 2014). Apparently, the risk associated with its supply and its importance for the industrial and economic systems are the most common aspects of material criticality.

1.2

Motivation of the study

Phosphate rock, the primary source of phosphorus used in crops and agricultural production, is finite (Cordell and White, 2014). The linkage between the agricultural industry and phosphorus is well established (Jones et al., 2013; Subba Rao et al., 2015;

Weikard, 2016). Even though several research studies show no sign of phosphorus shortage in the near future (Calvo et al., 2017; Cordell and White, 2013; Scholz et al., 2013; Wellmer and Scholz, 2017), any potential scarcity might directly affect the supply of agricultural products, especially in regions which must rely on imports as no primary phosphorus is available there. It means a serious disruption of food supplies which might affect global population (Nanda et al., 2019). While the agricultural sector relies heavily on phosphorus, demand for dairy livestock and healthy diets are growing rapidly, partly due to the population growth and changes in lifestyles. This pushes the agricultural industry to sustain the production to meet the growing demands.

During the economic crisis in 2008, phosphate prices surged with an increase equivalent to around 800%. This price change revealed volatility of the phosphorus market and vulnerability of importing countries (Cordell et al., 2015). The current linear models of phosphorus have shown excessive use of primary phosphorus within the natural P cycle, intensifying the criticality level of the non-substitutable element. Interestingly, resource shortage is not the only concern surrounding the topic. Other concerns are equally associated with the current P flows reflecting the environmental and social standards of societies. Environmental concerns from the linear P models include several stages throughout the supply chain. One of the major environmental concerns in the linear phosphorus cycle is its escape to the environment. Phosphorus from diverse sources or waste channels eventually finds its way to the aquatic environment. This leads to water pollution, known as eutrophication. That is one of the main reasons why we should re- think the current P cycle to tackle these global challenges.

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1.3 Problem definition 15

These issues drew attention and concern towards the sustainability of phosphorus management (Ulrich and Schnug, 2013). Therefore, focus shifted towards the recycling and recovery of phosphorus from waste streams to ensure the circulation of phosphorus material through its supply chain and to avoid environmental, economic and resource shortage problems in the future. Besides, the concept of circular economy was introduced to tackle the challenge posed by unsustainable use of phosphorus flows across the supply chain (Geissler et al., 2018a). This concept has been adopted to deal with waste generation issues, resource scarcity, and to sustain the economic benefits from economic systems (Van Hoof et al., 2018). In the case of phosphorus in particular, circular economy can potentially drive the supply chain towards a sustainable use considering the availability of the material from recovery and recycling (Withers et al., 2018).

This dissertation considers the ongoing research on phosphorus circular economy and its sustainable management. It is motivated by the wish to make a meaningful contribution to literature on closed-loop supply chains of the phosphorus flow management. Strategies for the sustainable development of phosphorus management are reflections of quantitative analyses and studies, which drive decision makers to seek experts and scientists in the field (Geissler et al., 2018b). First, a detailed analysis of phosphorus flows is outlined. It identifies shortages as well as the potential alternatives for conserving the material flow through the implementation of the circular economy. It also shows the significance of circular economy for tackling the challenge of phosphorus scarcity. Second, I analyse environmental and social impact of circular economy implementation on the phosphorus supply chain.

1.3

Problem definition

The need for a transition from linear models into a circular economic model of the phosphorus flows has been well established and proven in research (Geissler et al., 2018a;

Kasprzyk and Gajewska, 2019; Nättorp et al., 2019; Nesme and Withers, 2016; Robles et al., 2020).

Several studies considered the reversibility of the phosphorus chain in arriving at sustainable management of phosphorus flows through the circular economy (Chen and Graedel, 2016; Ott and Rechberger, 2012; van Dijk et al., 2016; Withers et al., 2018, 2015). While the circular economy in its reversibility concept might reduce mining, losses and vulnerability (Pietrzyk-Sokulska et al., 2015), the decision-making process often includes other aspects such as the environmental, social and economic pressures associated with recycling and recovery activities. Environmental aspects reflected in energy consumption and GHG emissions highly impact the sustainability performance of supply chains (Azadeh and Arani, 2016). Also, while the concept of material conservation and supply chain reversibility promises achievements in resource sustainability, the associated social and ecological values are often ignored and disregarded (Niskanen et al., 2020).

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From these discussions, we have learnt that circular economy model for the phosphorus supply chain is not yet fully discussed from multiple perspectives, i.e., resource, environmental and social. The analysis of phosphorus flows within a holistic approach from mining to recycling is missing together with immediate consequences of improving recycling efficiencies in reducing vulnerability.

Given the multiple views regarding the impact of circular economy on sustainability, the main aim of this dissertation is to analyse sustainability performance of the phosphorus supply chain within the circular economy approach.

1.4

Objective and research questions of the study

This study reflects on the importance of considering the multiple aspects of the phosphorus supply chain within the circular economy model. Hence, it aims to achieve the following objectives:

Objective 1: Determine the reduction in phosphorus criticality in circular economy model for regions highly dependent on imports.

Objective 2: Assess the environmental and social impact of circular economy on the phosphorus supply chain.

Objective 3: Examine the decisions regarding the implementation of circular economy model for phosphorus in regions with high vulnerability.

To achieve these objectives, four research questions are formulated:

RQ1: To what extent does circular economy mitigate the criticality of phosphorus for regions with high import-dependency?

RQ2: Does circular economy provide an environmentally friendly alternative for the phosphorus supply chain instead of linear models?

RQ3: Does circular economy contribute to the achievement of social development targets associated with the phosphorus supply chain?

RQ4: Do countries highly-dependent on imports make rational decisions in using secondary or primary phosphorus during the transition to circular economy?

1.5

Structure of the dissertation

This dissertation consists of five main chapters. Each chapter is divided into several sub- chapters. The first chapter explains the background of this research, it highlights challenges, the motivation behind the research and sets up clearly the objectives of the study. The second chapter discusses previous research on the criticality of phosphorus,

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1.5 Structure of the dissertation 17

the need for its recycling, and associated challenges regarding circularity implementation on the societies and the environment. The third chapter introduces used methodologies, including system dynamics and the Bayesian game theory. The chapter explains how these methodologies are used for serving the objectives of this research through schematic representations and mathematical formulas. The fourth chapter provides overviews of the publications included and their respective results and discussions. The fifth chapter provides the main findings and concludes overall results and the contribution of the research.

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2 Literature review

2.1

Phosphorus as a critical raw material

Phosphorus is a prominent material for all living beings. It is a crucial input for the food chain with no potential substitutes, and it is a major contributor to the fertilizers and agriculture industry (Belboom et al., 2015). In post-2008 economic crisis, the surge in prices of phosphate fertilizers has drawn attention towards the vulnerability of importing regions to the fluctuations of phosphorus price indices and the economic importance of the material in the food and crops production sector. Interestingly, P reserves are sufficient, and signs of their scarcity are not well proven. However, their availability is often influenced by geopolitical issues, economics and environmental policies (Schulz et al., 2017). Looking at the nature of phosphorus, it plays a vital role in well-being development, has no alternatives and substitutes, and its natural resource (phosphate rock) is unequally distributed around the world. Hence, many studies have classified the element phosphorus as a critical raw material.

2.1.1 Phosphate rock

Phosphate rock (PR) is by far the only major source for obtaining phosphorus element globally (Ober, 2018). The primary concern is the vulnerability of phosphorus availability to PR limitations. The prices of PR have always followed a stable trend, while experiencing some price spikes that have occurred during significant events such as post- World War II and 2008 economic crisis. These price surges have impacted food prices directly (Mew, 2016). Currently, PR reserves are estimated to reach up to 290 Gt worldwide (Van Kauwenbergh, 2010), from which 69 Gt is extractable according to the latest report by the United States Geological Survey (USGS). Annually, PR production accounted for around 240 million metric tonnes worldwide in 2019, where China, United States, Morocco, and Western Sahara continue to dominate the world production volumes (Jasinski, 2019). This unequal geographical distribution highly influences the prices of fertilizers, crops, and food (Schoumans et al., 2015).

The interest in phosphorus availability has its basis in understanding the phosphate rock reserve data (Cordell et al., 2009). While estimated peaks have been concluded around 2070, other research argue that PR reserves are sufficiently available to sustain production well beyond the 21^st century (Sverdrup and Ragnarsdottir, 2011; Van Vuuren et al., 2010).

Regardless of the global availability argument, the fact that the global distribution of phosphate rocks is limited to major country producers puts other regions such as Europe in a highly vulnerable situation, where dependency on P imports is up to 90% (Blengini et al., 2017).

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2.2

Phosphorus flow – from mining to recycling

Phosphorus natural cycle is driven by strong demand for P represented by fertilizer, food and feed additives industries, recipients of over 90% of P flows (Metson et al., 2016).

Phosphorus flow takes place in four subsequent steps including the industrial stage (Chen and Graedel, 2016; Koppelaar and Weikard, 2013; Scholz and Wellmer, 2015), the production stage (Belboom et al., 2015; Mottet et al., 2017; Noya et al., 2017; Van Hoof et al., 2017), the consumption stage, and the dissipation and recycling stage (Fowdar et al., 2017; Harris et al., 2017; Hobbs et al., 2018; Leon and Kohyama, 2017). Life cycle stages include mining, processing, production, consumption waste generation, landfilling and recycling, while the rest is lost at each life cycle stage

2.2.1 P industrial stage

The industrial stage starts with the mining of raw phosphorus in the form of apatite from phosphate rock. Phosphate rock contains up to 15% of pure phosphorus (Gilbert, 2009).

Mining is followed by the beneficiation stage, which corresponds to the washing and screening of the phosphate rock materials. The beneficiated material is processed into phosphoric acid using, inter alia, wet chemical processes.

2.2.2 P production and consumption stage

The production stage consists of diverse processes taking place in multiple industries, such as chemical fertilizer, food additives, and feed additives industry. The rest, in the form of Sodium Triphosphates (STTP), is used in the production of laundry detergents and in other industrial uses (Makara et al., 2016). Production of chemical fertilizers is followed by the production of crops with the application of P-enriched fertilizers, while additives are used for feeding the livestock populations.

The consumption stage covers human intake of phosphorus through nutrients and food supply. Dairy products, meat, crops, processed food and food additives are the channels of P consumption. In post-consumption stages, phosphorus accumulates in three major waste streams including wastewater, manure, and solid waste.

2.2.3 P dissipation and recycling

Manure is considered the largest stock of phosphorus waste generated by livestock. P in wastewater comes from human excreta, and detergents, while P in solid waste comes from food waste. Food waste flows are generated by wholesale and retail trade, food-related services, and households (Stenmarck et al., 2016).

The treatment of phosphorus within the major waste streams takes place separately.

Wastewater is considered a rich source of phosphorus, with around 4% of P in wastewater sludge (Kalmykova and Karlfeldt Fedje, 2013). Phosphorus from wastewater is treated using several methods including the common technique of anaerobic digestion (Wang et

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2.3 The closed loop of phosphorus 21

al., 2020). Anaerobic digestion method leads to the formation of sludge in its solid state, before obtaining organic phosphorus that can be used in farmland applications as an organic derivative. Food waste contains much less phosphorus, only 4g of P per kilogram of food waste (Kalmykova and Karlfeldt Fedje, 2013). Besides, manure is the source with the largest share of organic fertilizers (Loyon, 2017). Recycled manure often goes directly to fields, which is why it is used predominantly in agricultural applications (Buckwell and Nadeu, 2016).

2.2.4 P losses and landfilling

P losses occur along the supply chain from mining to waste treatment processes. Most of the lost phosphorus ends up in the marine system. In the industrial stage, P is lost during the mining, beneficiating, and processing in the form of phosphorus tailings, slags and mine slimes (Chen and Graedel, 2016). In the production stage, phosphorus is lost in post- application of fertilizers to the farmlands, during the process of runoff, soil erosion, soil loss, and leaching (Ortiz-Reyes and Anex, 2018), where phosphorus tends to attach to soil particles and moves into the surface-water bodies (Chen and Graedel, 2016).

Simultaneously, phosphorus is lost during the laundry detergent production processes and other industrial uses and often ends up in the waterbodies. Additional losses occur through industrial wastewater (Hobbs et al., 2017), crops harvesting, animal and food production (Maguire and Fulweiler, 2017). Lost P can also be tracked through food waste, human excreta and household waste sources (Chen and Graedel, 2016). During waste generation and collecting processes, losses occur through the effluents of P in wastewater into the marine system.

Considering various channels through which P is lost from mining to recycling, estimates show that almost 80% of mined phosphorus is not being used, instead, it ends up in water ecosystems (Nedelciu et al., 2020). This shows very low efficiency of phosphorus natural cycles, and a need to improve them by blocking the loss channels and ensuring a reversal flow from which supposedly lost phosphorus could be brought back again into the supply chain.

2.3

The closed loop of phosphorus

A closed-loop system is a concept, in which materials can be reused by being returned into the supply chain after the consumption stage. It covers the treating, recycling, and recovery of waste materials. Consequently, a circular economy has emerged as a viable alternative for mitigating the vulnerability towards critical materials that are subject to supply disruptions (Busch et al., 2014). Also, the consumption pattern of resources has revealed the criticality of our resource situation. This urged policy and decision makers to consider a shift from linear economic models to circular ones (Ranta et al., 2018). In simple words, a circular economy is a concept aimed to conserve the value of materials within the economic systems for as long as possible (Cobo et al., 2018).

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Concrete proposals as to how phosphorus circular economy should be put in place vary widely within the scientific community and in regional policies as well (Rahimpour Golroudbary et al., 2020). Geissler et al (2018b) address the blockage of loss channels across the P supply chain as an initiative to achieve phosphorus circular economy. Egle et al (2016) consider P recovery and recycling from sewage sludges with an estimate recycling efficiency of 95%. Also, Kraus and Kabbe (2017) consider P recovery from effluents in wastewater treatment plants (WWTP), with a recovery rate ranging between 20 to 45% through the removal of biological phosphorus. Mehr et al (2018) go further by including multiple waste streams of the phosphorus supply chain into the recycling alternative as a circular economy initiative. On the regional level, proposals for the implementation of circular economy models have been made in several studies (European Commission, 2018; Geng et al., 2012; Magnier, 2017; PBL, 2018; Velenturf and Jopson, 2019; Wijkman and Skånberg, 2016). Recycling is by far the most common component of circular economy solution proposed in these studies. It considers the correlation between material quantity and quality in supply chains (Cobo et al., 2018; Trochu et al., 2018). It also serves the core objective of conserving the material value within supply chains as much as possible (Ellen MacArthur Foundation, 2017). For the phosphorus chain particularly, closing the P cycle demands changes in the treatment processes of waste streams in post-consumption stages, such as improving the collection, treatment, and recycling (Dawson and Hilton, 2011; Mihelcic et al., 2011; Sharpley et al., 2016).

Proposals for phosphorus recycling have been introduced to tackle the criticality of the material in several studies (Childers et al., 2011; Cordell et al., 2011; Roy, 2017; van der Kooij et al., 2020). Manure, wastewater and solid waste are significant sources for secondary phosphorus (Kalmykova et al., 2012), and they are by far the primary sources in which recycling and recovery activities take place (Haase et al., 2017; Pearce and Chertow, 2017; Shiu et al., 2017). Experimental studies have shown the significance of P recovery from wastewater, considering the quality as well as the techniques applied in wastewater treatment (Kumar and Pal, 2015; Musfique et al., 2015). They can provide supplementary sources for fertilizers stocks (Ye et al., 2017). For instance, P recycling from different waste streams can potentially meet up to 30% of national demand (Cordell, 2010). Despite the significant improvements recycling could bring to the phosphorus supply chain within a circular economy design, it is important to consider the environmental and the social side of the story.

2.4

Environmental sustainability of phosphorus

Environmental performance along the phosphorus supply at each stage is crucial to understand its sustainability. Environmental burdens resulting from the depletion of energy sources and the growth in greenhouse gas emissions can be obviously witnessed in the phosphorus supply chain (Azadeh and Arani, 2016). The continuous growth in agricultural production is followed by growing trends in the mining and recycling patterns to meet ongoing demands (Wu et al., 2017). This will obviously impact energy consumption and GHG emissions associated with the supply chain. Several

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2.5 Social sustainability of phosphorus 23

environmental costs can be attributed to the current P flow management, including freshwater eutrophication; energy-intensive mining, processing and production;

excessive use of water; GHG and other toxic emissions (Scholz and Wellmer, 2016). The chain of fertilizers production – where phosphorus is a predominant element – contributes heavily to global environmental challenges (Zhang et al., 2017).

Several research suggest that a circular economy model is capable of solving environmental problems without compromising the economic benefits of supply chains (Gregson et al., 2015; Lazarevic and Valve, 2017). Calls have been made to move from linear models into circular models and change the current production patterns to curtail the growing environmental burdens (Geissdoerfer et al., 2017; Kirchherr et al., 2018).

The transition to circular economy should go in parallel with sustainable environmental performance of the supply chain (Elia et al., 2017). However, while the focus is on replacing primary P production with secondary production, energy demands from the recycling processes are often overlooked (Cullen, 2017). The shift to the recovery of phosphorus from waste streams as a secondary source of supply leads to an increase in energy demands, GHG emissions and a higher acidification potential (Amann et al., 2018). Therefore, deep insights into the environmental performance of phosphorus circular economy is urgently required (Tonini et al., 2019).

2.5

Social sustainability of phosphorus

Several social issues are associated with the phosphorus supply chain. Issues such as societal health, human rights, labour safety, nutrition security and national equity have their impact along the different stages of the phosphorus life cycle (Teah and Onuki, 2017). These challenges have already been included in the United Nations (UN) report on sustainable development goals, many of which correspond to the fundamental societal and human needs (United Nations, 2019). Agricultural production contributes to around 30% of global employment (World bank, 2020). Also, the same sector is responsible for 70% of global child labour (FAO, 2020). In addition, up to 70% of global freshwater withdrawals go to the agricultural sector alone (FAO, 2017). While more than 90% of phosphorus flows end up in agriculture (van Dijk et al., 2016), the phosphorus supply chain is partially responsible for growing social concerns concerning employment, malnutrition, livelihood and water use and supply.

From a circular economy perspective, significant progress should be reflected inachieving and fulfilling societal needs (Alaerts et al., 2019). Systems adopting the concept of material conservation should be a means for improving human well-being and achieving high quality of life (Griggs et al., 2013; O’Neill et al., 2018). Unfortunately, previous analyses of the sustainable supply chain have focused on its economic and environmental sides, leaving the social perspective with no exploration (Mani et al., 2018). Martinez- Blanco et al. (2014) argue that social aspects of supply chains need to be scientifically assessed in many details.

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2.6

Research gap

The agricultural chain plays a vital role in the lives of human populations. The scale of the phosphorus supply chain and its economic importance motivates the evaluation of its impact on the environment and societies. This study highlights three research gaps. First, previous research lacks the assessment of circular economy impact on mitigating phosphorus criticality. Second, a holistic research on the environmental impact of phosphorus recycling from multiple sources is not available. This poses the unanswered question of whether a circular economy is a better alternative for the environment. Third, in the face of growing social issues globally, the social impact of the circular economy model implementation in the phosphorus chain is not researched.

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3 Research methodology

To accomplish its goals, this study adopts a quantitative approach. Major part of this analysis aims to assess the sustainability performance of phosphorus supply chain transition to circularity over time. Given the multiple dimensions (resource, environmental, and social), as well as the need for making future estimates and forecast, the study requires a methodology that can tackle the following issues:

(i) Estimation and forecast of future behavior of the phosphorus supply chain system

(ii) Understanding the interrelations and causal relationships between the different variables in the system

(iii) Analyze interrelated multi-systems. This includes the phosphorus supply chain and its environmental and social consequences

(iv) Analyze the decision makers’ behavior regarding the use of phosphorus sources

Therefore, two methodologies are used. First, system dynamics is used to model the phosphorus supply chain as a sub-system. Consequently, to address the environmental and social impact, environmental and social sub-systems are also modelled given the complexity of interrelationships between parameters and variables of the system holistically. Second, Bayesian game theory is used to determine the decision pattern of countries during the selection of the phosphorus sources to meet the ongoing demands.

3.1

System Dynamics

System dynamics modelling can simulate the real-world cases. Often, systems include complexity, nonlinearity, and causal interrelationships between multiple parameters and variables. This also applies to the supply chains of goods, products, and materials. System dynamics is appreciated for its capability of embracing these conditions and adapting them to represent the problem under study.

Central publications such as the ones by Forrester (1997) and Towill (1996) provide detailed insight into the usability of system thinking in modelling and managing the industrial supply chains. System dynamics methodology transforms the supply chains under the study from their static nature into a computer-based level where level and rate equations are created to describe the system behaviour numerically over time.

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3.1.1 System dynamics process

According to J. Forrester (1994), the system dynamics process follows a 6-steps approach, in which the first four contribute heavily to systemic design of the phosphorus supply chain (Figure 3.1). First, it starts with the system description. This includes the modelling of the material flow from mining to recycling, and the desire to understand the system behaviour and the correlations, interrelations, and dependencies between the different variables and parts of the supply chain. Second, the simulation model is formulated by transforming the system description and behaviour into mathematical level and rate equations. Third, the system is run and simulated. This provides the current dynamic behaviour of the supply chain components as a reflection of the real-world situation supposedly. It also provides an overview of troubling issues and stages and opens the discussion for improvements. Fourth, alternatives are identified to achieve a desired outcome as in the scenario building exercise. This leads back to the very first step where the alternative system is re-described and eventually mathematical formulations and rate equations are updated.

3.1.2 Causal loop conceptualization

The system dynamics model is represented through the set of feedback loops that enhance the dynamic behaviour of the examined system. For the phosphorus supply chain, feedback loops can be represented as reinforcing and balancing loops. A reinforcing loop reflects the ice-berg effect from which a variable in the system produces action. It triggers an effect that reinforces the same (primary) action. Reinforcement may evolve in either positive or negative direction. On the opposite side, a balancing loop performs an action that tries to bring things to a desired state and eventually maintain the status or achieve the target . It is often used for setting goals and objectives to be met and achieved.

Figure 3.2 is a schematic representation of the feedback loop structure of the phosphorus supply chain. There are seven major feedback loops in the phosphorus supply chain considered in this dissertation. Six out of them are balancing loops:

- B1: refers to the relationship between agricultural production, consumption, demand for food, and agricultural demand. Agricultural demand will trigger the production of agricultural sector resulting in higher availability of food for

Figure 3.1: Process of the system dynamics modelling.

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3.1 System Dynamics 27

consumption. This will decrease the pressure of demand for food, eventually decreasing the demand for agriculture processes.

- B2: refers to the relationship between agricultural demand and production; higher demand translates into higher rates of production. This will decrease the pressure of agricultural demand.

- B3: refers to the relationship between food demand and consumption. Higher demand for food leads to higher consumption. However, the higher the consumption, the smaller the demand for food.

- B4: refers to the relationship between mining, processing, and agricultural production. Phosphate rock mining influences the processing and agricultural production. However, higher agricultural production also leads to less intensive mining processes.

- B5: refers to the relationship between mining, processing, detergent production, waste generation, and recycling. More mining leads to higher rates of detergent production and waste generation. This leads to a wider availability of material offering the recycling potential. Naturally, recycling alleviates the pressure on mining leading to lower rates of phosphate mining.

- B6: refers to the relationship between detergent demand and production. Similar to loops B2 and B3.

There is one reinforcing loop:

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- R1: refers to the relationship between phosphorus recycling, agricultural production, consumption, and waste generation. Phosphorus obtained from recycling should be used in fertilizers, creating the positively influential loop.

3.1.3 Stock and flow dynamic modelling

Having understood the major interactions and feedback loop structure of the phosphorus supply chain, the next step is to create stock and flow diagram using the causal loop concept as shown in Figure 3.3. Stocks and flows are by far the foundation of a system dynamics model. Originally, Forrester (1997) referred to them as levels and rates. A flow variable is measured per unit of time. Stocks, however, correspond to the accumulation

Figure 3.2: Causal loop diagram for the phosphorus supply chain.

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that has resulted from flows across the stock (input and output). Thus, it is measured at a certain time by including all flows since the simulation model has started.

In this dissertation, the stock and flow diagram represent the phosphorus supply chain from mining to recycling. Also, in later stages, the environmental as well as the social indicators are added subsequently to the structure of the stock and flow diagram of the phosphorus chain.

3.1.4 Material flow of the phosphorus supply chain

The material flow modelling process is effectively used in viewing the sustainability level of material flows, as it explicitly shows from where material is sourced, and where it is heading (Kaufman, 2012). It is a tool used in the assessment of material circularity (Balanay and Halog, 2018). Inputs, outputs, and stocks are the elements from which a material flow model can be designed. It shows the flow pattern of material within the associated area. The modelling process of the material flow correlates with the well- known method of material flow analysis (MFA), which dates back to the 1990’s (Brunner and Rechberger, 2016; Van der Voet et al., 2002).

The design of phosphorus flow in this study is motivated by the need to track the flow of phosphorus across the multiple stages in its supply chain. The general view is that a significant amount of phosphorus is lost. The current research concern is to identify the quantities entering the system, escaping, and returned into the system, loss channels, and possible optimization scenarios. Hence, the flow pattern in this study answers the questions:

Figure 3.3: Conceptual model of the regional phosphorus supply chain (El Wali et al.

2019).

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i. How much phosphorus does enter the system?

ii. How much phosphorus does escape from the system?

iii. How much phosphorus is recycled?

iv. Where are the loss channels?

To address these questions, a clear design of the material flow model should be prepared.

This model includes both ends of the system: mining and recycling. Also, the boundaries of the system should be defined.

This study addresses regional, continental, and global scales. Therefore, the system boundaries of the phosphorus flow model vary accordingly. The conceptual design of the phosphorus model is taken and compiled from various literature sources. Input data come from the existing literature, as well as databanks.

When designing the phosphorus flow model, five principles need to be borne in mind:

• The model is a designed material flow system and is not attributed to a particular material flow.

• The conservation of material flow unit is crucial to ensure consistency between flow channels.

• Each stage of the material flow includes a description of the state of the flowing material (i.e., chemical or physical state).

• The presentation of results is numeric based and diagrammatic.

3.1.5 Environmental sub-model design

This study takes a closer look at mining, processing, and recycling of phosphorus as the major contributors to energy consumption in the phosphorus chain. While mining refers to the extraction and mining of raw phosphate rock, processing refers to the production of chemical P-enriched fertilizers, feed and food additives, and recycling means manure, solid waste, and wastewater recycling to obtain organic P fertilizers to be used directly in the agricultural sector.

In this study, energy required for the phosphorus supply chain means the amount of energy necessary to fuel phosphorus flows. By far, there are six types of energy used, including oil, natural gas, petroleum, nuclear gas, hydroelectrical energy, and other energy from renewable sources.

Energy required for the mining phase covers energy used by mining machines and equipment, including the use of draglines, pumps, pit cars, pumping, beneficiation, and transport of raw material to the processing sites (Schroder et al., 2010). Energy required for the production or processing phase goes for the production of fertilizers, as well as the feed and food additives. For the production of fertilizers, the slurry method is the primary

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one used to produce mono and di-ammonium phosphates. Those are by far the most commonly used P fertilizers in agriculture (Zhang et al., 2017). Hence, the study includes the demand for energy needed to apply the slurry method. Energy required for feed processing is included in feed production (Frorip et al., 2012). In the recycling phase, energy demand for P recovery and recycling from manure, solid waste, and wastewater is considered. In wastewater recycling, wet chemical approach and the thermo-chemical treatment are commonly used for phosphorus recovery from sludge (Appels et al., 2010).

Therefore, energy demand for those processes was obtained as input data to the model.

For manure, energy demand is limited to the transportation of manure to agricultural land (Sandars et al., 2003). The solid waste source of recovered phosphorus requires energy for source separated collection. Unlike other methods, this method is meant to treat waste as composted fertilizers (Buratti et al., 2015).

In this study, GHG emissions occur from energy that is consumed directly. Therefore, the GHG sub-model depends on energy flows sub-model. This is important to mention, as GHG is often emitted from the phosphorus chain due to other causes such as manure storage, agriculture, and land processing …etc. Carbon dioxide, nitrous oxide, and methane are the most common GHG emissions. Like the energy consumption sub-model, the GHG emissions analysed in this study come from mining, production, and recycling.

Figure 3.4 is a schematic representation of the relationship between the phosphorus supply chain and environmental issues associated with its life cycle stages. The figure clearly shows the three sub-models, with the phosphorus flow model to be the main contributor or the main predictor of environmental consequences through (i) energy required for fuelling phosphorus flow processes, and (ii) the GHG emitted as a result of the energy consumed.

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3.1.6 Social sub-model design

This dissertation uses the social life cycle assessment (S-LCA) in adding the social aspects into the phosphorus supply chain. S-LCA is meant to be a derivative of the life cycle assessment methodologies, from which the social welfare is analysed. Fava et al.

(1993) is considered to be the central publication for the implementation of S-LCA.

Typically, life cycle assessments have been used extensively in analysing the environmental consequences of product or material systems. The proposals by Fava et al.

(1993) considered the social impact of products and systems within the spectrum of the life cycle assessment. The S-LCA is meant to assess the social impacts of materials across their life cycle. This life cycle starts from the mining of raw resources, ending up with the disposal or recycling of the material.

The process starts by defining the stakeholders for whom the social assessment will be measured. The identification of stakeholders is important because it determines the selection of social indicators. Like the environmental assessment of the phosphorus

Figure 3.4: Conceptual model of the phosphorus supply chain and its environmental indicators (Golroudbary et al. 2019).

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supply chain, social indicators are added to the phosphorus flow model holistically.

Figure 3.5 depicts the conceptual idea of the phosphorus flow model and the social impact assessment basis. This study takes account of the social hotspots along the phosphorus supply chain. They highlight the life cycle stages where social issues are likely to occur.

Altogether, there are nine social issues identified in this study, most of which occur in the mining, production, and recycling stage.

Each social indicator is related to a specific stakeholder. The building of the relationship between the social indicators and stakeholders is a sensitive exercise. For instance, when dealing with poverty, since only the livelihood of workers within the supply chain of phosphorus is included in this indicator, conclusions drawn for poverty within the whole community are thus misleading. Likewise, the employment indicator considers the employment contribution to the community rather than specifically the workforce engaged in the phosphorus supply chain. Hence, local communities are the parent category for employment indicator.

The issues related to the workers category concern work safety, gender equality, and employees’ livelihood. Work safety corresponds to the level of fatal and non-fatal accidents (including injuries) that take place at a workplace. It is an important indicator that measures the overall decency of working environments. To measure gender equality, this study considers the contribution of potential workers of both genders (male and female) to employment. Debates have been raging regarding the validity of such analyses.

Determination of gender shares in the workers’ population employed in the phosphorus chain does not reflect equality, for the simple reason that workers of a particular gender might not be seeking employment within this particular supply chain. A better picture could be achieved by measuring the size of workforce willing to find a job there and compare it to the gender structure of recruited individuals. Therefore, this study considers ratio of the employment rate for females to that of males. Employees’ livelihood measures the employee’s earnings from the job. It is directly related to the poverty measures, which

Figure 3.5: Conceptual model of the phosphorus supply chain and its social indicators (El Wali et al. 2021).

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identify a threshold (value of earnings per day) that should be met to ensure the least acceptable working environment for workers.

Social issues associated with local communities include child labour, nutrition supply, water use, and employment rates. Child labour measures the child engagement in economic activities related to the phosphorus supply chain. The reason it is included in the community’s category is its direct effect on the child population of the nation. It reflects the share of child population engaged in labour. Nutrition supply reflects the amount of phosphorus available for direct human consumption. Human body is highly vulnerable towards phosphorus shortage. Hence, the availability of food rich in phosphorus is important. Water use is directly related to the wellbeing of humans. Access to safe drinking water is getting more difficult as the world's population grows.

Furthermore, the agricultural sector accounts for roughly 70% of global freshwater withdrawals. The amount of water withdrawn for agriculture is equal to the amount of water required for crop production and cultivation. Employment rates are directly related to the communities as far as the national labour force is concerned. This study aims to analyse the contribution of phosphorus circular model to national employment. Hence, the measurement is based on the share of workers representing the national labour force (or global labour force within a global scale) employed in the phosphorus chain.

Societal and social issues relate to phosphorus efficiency as well as its security. Security of phosphorus supplies strongly impacts food security for any country. Without phosphorus, the food chain would potentially get disrupted. Phosphorus security is measured through the national reliance on foreign exporters and/or the mined phosphorus.

The goal is to achieve national independence through material conservation, which goes totally in parallel with the concept of material circularity or the circular economy. On the other hand, phosphorus efficiency refers the input-output ratios. Keeping in mind that agricultural production is by far the major source of phosphorus flows, the balance of phosphorus inputs as fertilizers and crops is measured. The lower the balance, the better the efficiency achieved by society.

Table 3.1 shows social indicators, their definitions, and respective stakeholders. At a later stage, they will be used to develop respective mathematical formulas for the phosphorus supply chain.

Table 3.1: Definition of social sustainability indicators in the phosphorus supply chain (El Wali et al. 2021).

Stakeholder category

Category impact

indicators Definition

Workers Work safety Reflects the health status of directly employed workers

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Employment equality

Reflects the employment contribution towards gender equality (male/female)

Livelihood of workers

Quantifies the number of employees living under poverty threshold

Local communities

Nutrition supply

Refers to the availability of nutrients for society, higher values or values above the threshold show that the nutrition system is good

Water use Measures the amount of water withdrawn for agricultural production

Employment rate

Measures the employment contribution to the local communities at the national level

Child labour Measures the child population involved in economic activities

Society

P efficiency

Refers to the balance of P between inputs as fertilizers and outputs as harvested and cultivated crops.

P security Reflects the domestic availability of P without dependence on imports.

The impact pathway assessment method (IPS S-LCA) is used to analyse the social consequences of the phosphorus supply chain. It is a bottom-up approach from which the social outcomes are estimated by following the pathway back to the source, which in this case represents the phosphorus material flow. For that, values of the social indicators initially are obtained per one functional unit of phosphorus flow, which corresponds to the inventory data used. Like the environmental analysis of the phosphorus chain, this dissertation assumes 1 tonne of phosphorus to be a functional unit.

3.1.7 Mathematical formulas

As mentioned earlier, stocks and flows are by far the fundamentals of the system dynamics modelling. The dynamic behaviour of a stock in the period t-t0 is given by a time integral of the net inflows minus the net outflows. This can be represented through the following equation:

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𝑆𝑡𝑜𝑐𝑘 (𝑡) = ∫(𝑖𝑛𝑓𝑙𝑜𝑤 (𝑡) − 𝑜𝑢𝑡𝑓𝑙𝑜𝑤 (𝑡))𝑑𝑡

𝑡

𝑡𝑜

+ 𝑆𝑡𝑜𝑐𝑘 (𝑡₀) (3.1)

The dynamic behaviour of flow is represented by the time derivative of the amount of material in the stock at time t. This can be reflected through the flowing equation

𝐹𝑙𝑜𝑤 (𝑡) =𝑑𝑥

𝑑𝑡 (3.2)

Where 𝑥 is the quantity of units (i.e., phosphorus material) in the stock.

Mathematical formulas for calculating energy consumption and GHG emissions reflect the dependency shown in Figure 3.4. The three major stages of phosphorus flow considered for analysing the environmental sustainability are represented by 𝑚, where 𝑚 = 1, 2, 3 (mining, processing, and recycling). There are 6 types of energy to fuel phosphorus flows, denoted by 𝑛, where 𝑛 = 1, 2, 3, 4, 5, 6 (coal, oil, gas, nuclear, hydroelectrical, and other renewables). The different types of GHG emitted from the energy consumption are represented by 𝑥, where 𝑥 = 1, 2 ,3 (CO2, N2O, and CH4). The results are obtained at time 𝑡, where 𝑡 is any time between 2000 and 2050.

The mathematical formulation of energy consumption at time 𝑡 equals to:

𝐸𝐶_𝑚(𝑡) = 𝑃_𝑚(𝑡) × ∑ 𝜎_𝑚,𝑛

6

𝑛=1

(3.3)

Where 𝐸𝐶_𝑚(𝑡) is energy consumption at life cycle stage 𝑚, and 𝜎_𝑚,𝑛 is the energy of type 𝑛 required per one tonne of phosphorus flow at stage 𝑚.

The mathematical formula for the GHG emissions at time 𝑡 equals to:

𝐺𝐻𝐺_𝑥,𝑚(𝑡) = 𝐸𝐶_𝑚(𝑡) × ∑ 𝛿_𝑥,𝑛

6

𝑛=1

(3.4)

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Where 𝐺𝐻𝐺_𝑥,𝑚(𝑡) refers to the amount of greenhouse gas emissions of type 𝑥 at life cycle stage 𝑚; 𝐸𝐶_𝑚(𝑡) is the energy consumption at life cycle stage 𝑚; and 𝛿_𝑥,𝑛 is the amount of greenhouse gas emitted of type 𝑥 per 1 joule of energy consumed from source 𝑛.

To analyse the social impact, this dissertation provides mathematical formulas of the nine social indicators. The stages in which the social issues are likely to occur in this study are represented by 𝑚, where 𝑚 = 1, 2, 3 (mining, agriculture production, and recycling). The analysis is carried out at time 𝑡, where 𝑡 is any time between 2010 and 2050.

• Work safety is measured by the number of accidents (𝐴𝑐(𝑡)) occurring at workplace. It includes fatal and non-fatal accidents, 𝐴𝑐_𝑓 and 𝐴𝑐_𝑛𝑓 respectively:

𝐴𝑐(𝑡) =∑³_𝑚=1(𝐴𝑐_𝑓_𝑚(𝑡) + 𝐴𝑐_𝑛𝑓_𝑚(𝑡))

∑³_𝑚=1𝐸𝑝_𝑚(𝑡) × 𝑃_𝑚(𝑡) (3.5)

where 𝐸𝑝_𝑚(𝑡) is the number of employees available to produce one tonne of phosphorus at supply chain stage 𝑚; and 𝑃_𝑚(𝑡) refers to the flow of phosphorus at stage 𝑚

• Gender equality (𝐺𝐸(𝑡)) in the phosphorus chain is represented through the ratio of employment rates of female to male at stage 𝑚. The mathematical formula is as follows:

𝐺𝐸(𝑡) = ∑³_𝑚=1𝐹_𝑚(𝑡) ∗ (𝐿𝑓(𝑡))⁻¹

∑³_𝑚=1𝑀

𝑚(𝑡) ∗ (𝐿𝑚(𝑡))⁻¹ (3.6)

where 𝐹_𝑚(𝑡) is the number of female employees engaged at stage 𝑚; 𝑀_𝑚(𝑡) is the number of male employees engaged at stage 𝑚; 𝐿𝑓(𝑡) and 𝐿𝑚(𝑡) are the labour force for males and females at time 𝑡 respectively.

• The livelihood of employees is measured through the share of employees living under the poverty line (𝑃𝑜𝑣(𝑡)). It is calculated as follows:

𝑃𝑜𝑣(𝑡) = ∑³_𝑚=1𝜇_𝑚(𝑡)

∑³_𝑚=1𝐸𝑝_𝑚(𝑡) × 𝑃_𝑚(𝑡)× 100 (3.7)

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where 𝜇_𝑚(𝑡) is the number of workers living below the poverty line at stage 𝑚; and 𝐸𝑝_𝑚(𝑡) is the number of workers required to produce 1 tonne of phosphorus at stage 𝑚; and 𝑃_𝑚(𝑡) is the flow of phosphorus at stage 𝑚.

• The nutrition supply (𝑁𝑆(𝑡)) represents the amount of phosphorus available for immediate consumption. The calculation is as follows:

𝑁𝑆(𝑡) =𝑃_𝑎(𝑡) + 𝑃_𝑏(𝑡)

𝑃𝑜𝑝(𝑡) (3.8)

𝑃_𝑎(𝑡) and 𝑃_𝑏(𝑡) are the annual food production of crops and livestock at time 𝑡, respectively; and 𝑃𝑜𝑝(𝑡) is the annual population variable.

• Water use shows water used by agriculture. The equation of water use (𝑊(𝑡)) is given below:

𝑊(𝑡) =∑²⁰_𝑥=1𝐶𝑟_𝑥(𝑡) × 𝑊_𝐶𝑟_𝑥

𝑃𝑜𝑝(𝑡) (3.9)

where 𝐶𝑟_𝑥(𝑡) is the crops production of type 𝑥 = 1,2, … ,20; and 𝑊_𝐶𝑟_𝑥 is water required to grow one tonne of crop 𝑥.

• The employment rate (𝐸𝑚(𝑡)) corresponds to the share of labor force employed in the phosphorus supply chain in a country. The mathematical formula is as follows:

𝐸𝑚(𝑡) =∑³_𝑚=1𝐸𝑝_𝑚(𝑡) × 𝑃_𝑚(𝑡)

𝐿𝑏(𝑡) × 100 (3.10)

where 𝐸𝑝_𝑚(𝑡) is the number of employees needed for producing one tonne of phosphorus at stage 𝑚 at time 𝑡; and 𝑃_𝑚(𝑡) is the mass flow of phosphorus at stage 𝑚 at time 𝑡; and 𝐿𝑏(𝑡) is the labour force seeking employment regardless of the sector.

• Child labour is the percentage of child population engaged in the supply chain of phosphorus (𝐶𝑙(𝑡)). It is calculated as follows:

𝐶𝑙(𝑡) =𝑐𝑙(𝑡) × (𝐶𝑟(𝑡) + 𝐹_𝑑(𝑡))

𝐶ℎ(𝑡) × 𝑃𝑜𝑝(𝑡) × 100 (3.11)

Sustainability of phosphorus supply chain : circular economy approach

SUSTAINABILITY OF PHOSPHORUS SUPPLY CHAIN - CIRCULAR ECONOMY APPROACH

Mohammad El Wali

SUSTAINABILITY OF PHOSPHORUS SUPPLY CHAIN - CIRCULAR ECONOMY APPROACH

Abstract

Acknowledgements

Contents

List of publications

Author's contribution

Nomenclature

1 Introduction

1.1

1.2

1.3

1.4

1.5

2 Literature review

2.1

2.2

2.3

2.4

2.5

2.6

3 Research methodology

3.1