The dimensions of Lean-Green 4.0 readiness a Systematic literature review

Abstract

Lean-Green management is deployed in all organizational areas and sectors, but it is not yet understood how Lean-Green practices will progress in this digitalization era. This paper proposes a baseline framework to design an assessment model for implementing Lean-Green management in an Industry 4.0 environment. A systematic literature review was conducted to investigate the literature on Lean, Green and Industry 4.0. There is a gap in the literature related to the transformation of Lean-Green 4.0 management in organizations. Several dimensions were identified, namely: ‘leadership and strategy’, ‘people’, ‘process’, ‘product’, ‘customer’, ‘supplier’, ‘governance’, and ‘technology’. The measurement items, grouped into the dimensions, are proposed to illustrate what can be measured in the current state within organizations. This study bridges the gap between academia and practice by providing valuable insights to guide leaders in their journey to Lean and Green transformation. In addition, the findings provide new knowledge to leaders and academics concerning the most critical factors for a successful transformation. Management can adapt their organizations by knowing how to execute a Lean-Green system in the new digitalization era. This research aims to contribute to discussing the relationships between these two subjects.

Keywords:

• I4.0
• lean
• green
• digitalization
• Lean-Green

SUSTAINABLE DEVELOPMENT GOALS:

• SDG 8: Decent work and economic growth

1. Introduction

The continuous improvement methodology of Lean-Green is utilized to reduce non-value add waste and efficiently utilize resources (Duarte et al. 2020). In addition, Lean-Green enables organizations to improve their operational and environmental efficiencies by implementing actions to affect the environment positively (Farias et al. 2019). According to Toke and Kalpande (2018), Lean is a critical success factor for green implementation. To drive a good green system, several critical success factors are identified by Toke and Kalpande (2019) as examples (i) leadership commitment, (ii) societal concern for the protection of the natural environment, (iii) government policies and regulations, (iv) customer satisfaction and involvement, (vi) proper workplace management or (vii) reverse logistics practices. Similarly, Touriki et al. (2021) indicate various critical success factors for the implementation of a smart, lean-green, and resilient integrated model to achieve competitiveness and sustainability, like (i) corporate culture, (ii) communication, (iii) collaboration and corporation, (iv) leadership commitment, (v) training programs, (vi) management of expectations or vii) good project management.

Siegel et al. (2022) state that companies that have lean practices in their processes, and simply implement green, will stimulate process innovation and help companies to achieve improvements in terms of sustainability. That is, Lean practices are in line with green strategies and Lean-Green represents the evolution of Lean towards sustainability (Queiroz, Alves Junior, and Costa Melo 2022). Lean-Green really is an approach that all companies will have to apply in order to achieve competitiveness and sustainability, and for reach this companies need to think at a strategic, tactical, or operational level (Duarte and Cruz Machado 2017a)

However, with the advent of digitalization and Industry 4.0 (I4.0), organizations must define different methods of adding value to customers and how to design and make products and improve service delivery (Duarte and Cruz-Machado 2018). Applying information and communication technologies and their integration can incorporate business and engineering processes, making an intelligent environment. Furthermore, digitalization and extensive automation of systems enable more customization and individualization of products or services that will improve the value-add for customers.

The Lean-Green methodology and I4.0 are interrelated themes across all areas of manufacturing processes. The Lean management system and I4.0 can operate in parallel to each other and have a synergistic effect on each other, with Lean being a precursor for the efficiency and economic gains from I4.0 (Mayr et al. 2018) for the efficient and economical implementation of I4.0. Enke et al. (2018) give an opposing opinion and stated that increased digitization could not replace the value-added orientation of Lean processes to manufacturing via continuously improving through structured problem-solving, employee involvement, and strong leadership. Though Varela et al. (2019) point out many of the I4.0 elements that positively and negatively influence Sustainability; Toke and Kalpande (2019) affirm green technology is imperative for achieving sustainability and Enke et al. (2018) state that the effects of I4.0 on environmental and green initiatives are still little explored in relation to I4.0. Lately, Dahmani et al. (2021) mention that there are relatively few Lean-Green models that emphasize increasing system efficiency. Also, Queiroz, Alves Junior, and Costa Melo (2022) mention that the identified studies have not addressed the relationship between digitalization and Lean implementation or Lean-Green. So, there is still a need to develop frameworks that integrate Lean-Green (Dahmani et al. 2021; Zekhnini et al. 2022).

Indeed, a framework integrating these themes may be useful to provide pertinent information for decision makers before they make their decisions and can help to promote organizational learning (Ganjavi and Fazlollahtabar 2023). The vital link between operational excellence and Lean-Green enables of competitive advantage (Queiroz, Alves Junior, and Costa Melo (2022).

Therefore, evaluating Lean-Green implementation factors will aid organizations in becoming more productive and competitive (Duarte and Cruz Machado 2017a). However, the characteristics of the transition to Lean-Green systems within the Industry 4.0 era are undefined (Duarte et al. 2020; Duarte and Cruz-Machado 2018), and trade-offs can occur. A new model of support is required to understand these roadblocks (Kaswan et al. 2023). Companies can evaluate their level of Lean-Green implementation in the transition to I4.0, relative to all different functional areas . Different dimensions can be considered on this kind of model representing different areas of companies. Duarte (2023a) has put forward a basic readiness model for what they called Lean-Green 4.0. However, guidance and support are required to develop at a business implementation level. The research questions (RQs) or objectives for this study are to:

• RQ1: Review the literature to ascertain the characteristics of Lean Green and digitalization and review the current state of this area as a theme.

• RQ2: Propose a model for a Lean-Green management system within an Industry 4.0 environment to evaluate that transition.

This paper is organized as follows: in section 2, the systematic literature review methodology; in section 3, the definition of Lean-Green management is presented; and a brief review of literature on I4.0 is illustrated in section 3. Section 4 proposes a Lean-Green 4.0 assessment framework considering the dimensions and several items to be assigned. Finally, some concluding remarks are drawn.

2. Background to Lean-Green 4.0

2.1. Lean-Green management defined, benefits and characteristics

Lean-Green is a methodology to aid organizations in enhancing their performance (Duarte et al. 2020). Farias et al. (2019, Salvador, Piekarski, and Francisco (2017), and Zekhnini et al. (2022) discuss how the use of Lean-Green as an integrated management system is increasing. Several works confirm the approach for integrating Lean-Green (Duarte and Cruz Machado 2017a; Ramos et al. 2018; Salvador, Piekarski, and Francisco 2017; Tripathi et al. 2021; Verrier, Rose, and Caillaud 2016).

The adoption of the combined Lean-Green approach is due to their complimentary traits and positive benefits of their implementation deployment (Duarte and Cruz Machado 2017a; Ramos et al. 2018; Salvador, Piekarski, and Francisco 2017; Tripathi et al. 2021; Verrier, Rose, and Caillaud 2016). Also, the focus of the Lean-Green as a management systems approach comprises cross-organizational functions and processes and integrates into various sectoral and business themes (John, Sampayo, and Peças 2021).

There are examples of frameworks of Lean-Green integration within the literature. Duarte and Cruz Machado (2017a) put forward a Lean-Green framework to measure an organization via six criteria: (1) leadership, (2) people, (3) strategic planning, (4) stakeholders, (5) processes, and (6) results. Duarte and Cruz-Machado stated that these six criteria are interrelated, and by utilizing continuous improvement, enhanced results for organizations to achieve better operational structures can be achieved (Duarte and Cruz Machado 2017a). Verrier, Rose, and Caillaud (2016) discussed three pillars of Lean, Green, and Human factors. They stated that there are several different stages and ways to integrate and deploy Lean and green tools and principles within organizations, which validates the concepts of Lean-Green integration at all levels of the organization (Verrier, Rose, and Caillaud 2016). An approach to demonstrate the interlinkage between Lean Green across five functional areas, namely (i) supply chain management, (ii) quality management and performance, (iii) organizational culture, (iv) logistics and (v) product design and planning, was put forward by Salvador, Piekarski, and Francisco (2017). In a literature review study, Farias et al. (2019) stated that Lean-Green methods aided in enabling performance improvements which in turn can drive Lean-Green systems. Munoz-Villamizar and Santos (2021) found that the success of Lean-Green practices depended on (i) employee involvement, (ii) training provision, and (iii) leadership support and commitment. Munoz-Villamizar and Santos (2021) edited the Toyota ‘House of Lean’ by adding a Lean-green model as an extension with the inclusion of Lean tools, leadership commitment and lean-environmental training. A method focused on benchmarking to evaluate the management aspects of Lean-Green was put forward by Ramos et al. (2018), which evaluated (i) personnel, (ii) data, (iii) products, (iv) vendors, (v) customers, and (vi) processes, combining Lean practices to achieve a more eco-production system. More recently, Tripathi et al. (2021) developed a model applying to the I4.0 scenario, a smart Lean-Green approach. They suggested different guidelines for the success of their proposed model and are as follows: (i) the commitment of management team members and leadership, (ii) the application of lean tools; (iii) an efficient strategic planning; and (iv) a problem-solving approach (Tripathi et al. 2021).

In order to implement a Lean-Green management system, it is critical to include and integrate characteristics and principles that aid the business results and provide value to the end customer. Table 1 puts forward characteristics for the integration of Lean-Green. The integration of Lean and Green management is important to organizational performance and will need to adapt to I4.0 technologies (Duarte and Cruz-Machado 2017b).

Table 1. Lean-Green characteristics.

References Lean-Green characteristics	Verrier, Rose, and Caillaud (2016)	Rosário Cabrita et al. (2016)	Mittal et al. (2017)	Duarte and Cruz Machado (2017a)	Ramos et al. (2018)	Sanchez Rodrigues and Kumar (2019)	Bhattacharya, Nand, and Castka (2019)
Leadership participative and communication				X			X
Management commitment and support							X
Employee involvement	X			X			X
Employee training and development			X	X	X		X
Problem-solving skills	X			X	X		X
Flexible workforce			X	X
Organizational Objectives and Scope	X				X
Customer value		X	X	X
Cost reduction for all stakeholders		X					X
Customer satisfaction and loyalty	X			X		X	X
Supplier collaboration and involvement	X		X	X		X	X
Knowledge and information sharing				X	X	X
Continuous improvement	X			X			X
Elimination/Tracking of Waste	X					X	X
Process technology		X				X

2.2. I4.0 defined benefits and characteristics

I4.0 includes methods, technologies and digitization to optimize manufacturing processes and make them more autonomous, automated, systematic, flexible, and accurate (Mayr et al. 2018; Sanders, Elangeswaran, and Wulfsberg 2016). The Industry 4.0 world, with an increased focus on technology digitalization, is causing a redesign of industry practices (Ibarra, Ganzarain, and Igartua 2018). Creating interconnected systems by enhancing cyber-physical integration increases operational flexibility and productivity (Helming et al. 2019). I4.0 can enable technology changes in how organizations operate (Helming et al. 2019) and, thus, how they are digitally transformed (Schumacher, Erol, and Sihn 2016). Dillinger, Bernhard, and Reinhart (2022) defined I4.0 as an enhanced technology approach. I4.0 technology application success is contingent on several criteria, including having the right data and information to aid decision-making, the usability of the technology, approval of users, the assessment of any potential ethical, social or legal effects and opportunity for profitability (Mayr et al. 2018).

Müller, Kiel, and Voigt (2018) reviewed the opportunities for I4.0 implementation. They grouped them into categories related to strategic impact, effects on operations, the environment, and people, organizational competitiveness, and future market viability, whether or not the technology was an organizational match, and the ease of employee implementation and acceptance. In terms of a model that aids in deploying the I4.0 concepts in an organization, Doh, Deschamps, and Pinheiro De Lima (2016) grouped data by the technology, expected benefits, and type of applications. Schumacher, Erol, and Sihn (2016) proposed a maturity assessment model for I4.0 and expanded the focus on technology focus to include other organizational aspects. Their model included basic dimensions and 65 different criteria. These dimensions were (i) products, (ii) customers, (iii) operations, and (iv) technology, and as organizational dimensions of (v) strategy, (vi) leadership, (vii) governance, (viii) culture, and (ix) people. More recently, Wagire et al. (2021) also put forward a model for Industry 4.0 maturity with seven different dimensions related to (i) strategy, (ii) people and culture; (iii) knowledge and awareness of Industry 4.0; (iv) I4.0-based technology; (v) value chain and processes; (vi) smart manufacturing technology; (vi) product and services-oriented technology.

Ibarra, Ganzarain, and Igartua (2018) stated that perquisites for Industry 4.0 readiness are (i) organizational layout, (ii) process standardization, (iii) product availability, (iv) new business models, (v) having skilled personnel, (vi) intellectual property protection, (vii) research investment, (viii) personnel development, and (ix) legal processes and frameworks. In addition, enhancing digitalization involves technological applications and empowerment, and leadership is ready for these initiatives (Helming et al. 2019). There are many challenges within an I4.0 deployment and implementation, including technology, costs, and social, regulatory and political challenges (Zhou, Liu, and Zhou 2015). A summary of the challenges of I4.0 implementation from the literature is compiled in Table 2.

Table 2. I4.0 Characteristics.

References I4.0 characteristics	Schumacher, Erol, and Sihn (2016)	Müller, Kiel, and Voigt (2018)	Ibarra, Ganzarain, and Igartua (2018)	Mayr et al. (2018)	Helming et al. (2019)	Sony and Naik(2020)	Wagire et al. (2021)
Management support					X	X	X
Management competencies and methods	X					X
Management transparency				X	X	X
Employee training in new technology	X		X			X	X
Autonomy of employees	X			X
ICT competencies of employees	X					X	X
New business models	X	X	X			X
New value offers		X		X		X
Decentralization of decision making			X			X
Service orientation			X
Customer orientation			X			X	X
Environmental impact reduction		X				X
Resource allocation	X					X
Avoiding waste				X	X	X
Developing integral customer experiences			X			X	X
Cost reduction			X			X	X
Customer data	X		X			X	X
Process and products complexity			X	X		X	X
Real-time information			X			X	X
Individualization of products	X
Digitalization of products	X					X	X
Standardized and transparent processes				X		X	X

I4.0 integrates and crosses all aspects of an organization, a sector, or a society (Sony and Naik 2020). Sony and Naik (2020) put forward critical success factors in relation to I4.0 implementation. These were having a clear organizational strategy linked to I4.0, (i) leadership support, (ii) the right employees, (iii) smart products and services, (iv) a digitally enhanced supply chain and organization, (v) an effective change management process, (vi) good project management and (vii) Sustainability of the initiative.

3. Methodology – systematic literature review

This research is focused on understanding the relationships of Lean-Green with digitalization in terms of the literature and analysing the existing literature on Lean-Green and I4.0 to derive the implications of the Lean, Green, and I4.0 approaches. While much research has been conducted on the Lean, Green, and I4.0 areas, there has been little research on an assessment model for their readiness (John, Sampayo, and Peças 2021). The relationship of Lean-Green with I4.0 is a gap in the literature this research aims to fill (RQ1). The authors hope to put forward a model for a Lean-green management system transition in the I4.0 environment. This model will be based on a literature review of Lean-Green as a topic and I4.0 as a topic with a systematic literature review (SLR) focus on Lean, Green and I4.0 in particular as a combined theme.

Burgess, Singh, and Koroglu (2006) defined a SLR as studying selected articles searched from different databases and sources. Systematic review literature has been published within the operational excellence space related to topics such as Lean Six Sigma 4.0, Lean 4.0 and Quality 4.0 in the operations and quality management domain, focusing on various important topics (Antony et al. 2022; Garza-Reyes 2015; Sony, Antony, and McDermott 2023). Therefore, this research follows a systematic literature review approach to collecting and analysing published journal and conference paper articles. This study aims to follow a similar structure and methodology of selecting articles from specific journals as suggested by Tranfield, Denyer, and Smart (2003), Burgess, Singh, and Koroglu (2006), Petticrew (2001) and Massaro, Dumay, and Guthrie (2016).

There are several stages in a SLR (Figure 1), and the authors of this study have leveraged Tranfield, Denyer, and Smart (2003) and the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) approach for SLR. The SLR was carried out in 6 stages: the Planning Review, literature search method, defining inclusion and exclusion criteria, a quality assessment and review, and finally, conducting the review and analysis.

Figure 1. SLR flow chart.

Having reviewed the RQs, the search keywords were agreed including ‘LEAN-GREEN AND I4.0’, ‘LEAN, GREEN AND DIGITALISATION’, ‘LEAN-GREEN’, ‘LEAN, SUSTAINABILITY AND I4.0’, and ‘LEAN, SUSTAINABILITY AND DIGITALISATION’. The academic databases of Web of Science and SCOPUS were utilized, and peer-reviewed journal articles and conference papers or proceedings were part of the inclusion criteria for the search. Any articles or literature that were non-written in English or not published before 2013 were excluded. While the search aimed to select journals from the Association of Business Schools (ABS) rankings (Chartered Association of Business Schools 2021), some other listed journals were selected (e.g. Journal of Cleaner Production, The TQM Journal, the International Journal of Lean Six Sigma, etc.) were also included in this study, as they were publishing articles primarily around the chosen topic area. While many articles were found if ‘LEAN-GREEN’ were searched, these, while relevant, were not related to the I4.0 aspect of the research. Hence the researchers included I4.0 or digitalization in the search, but when the search was filtered with these keywords on I4.0/digitalization, these numbers were reduced significantly. After the final screening, removing duplicates, and reading abstracts for relevance to the research themes, the authors agreed to 28 papers for inclusion.

The shortlisted 13 journals are shown in Table 3. Again, there was a division between journal publications (75%) and conference publications (25%) based on the final 28 screened literature selections.

Table 3. List of journals.

1	Sustainability
2	Journal of Cleaner Production
3	Journal of Manufacturing Technology Management
4	International Journal of Production Research
5	Research in Transportation Economics
6	Production Planning & Control
7	Processes
8	Procedia CIRP
9	Journal of Open Innovation: Technology, Market, and Complexity
10	Journal of Engineering Design & Complexity
11	International Journal of Social Ecology and Sustainable Development
12	International Journal of Mathematical, Engineering and Management Sciences
13	IEEE Transactions on Engineering Management

Burgess, Singh, and Koroglu (2006) advised using keywords adopted for this study to aid the selection of papers and the screening and reading of papers. Accordingly, various themes, such as the definition of Lean-Green 4.0, the benefits of integrating Lean-Green and I4.0, the challenges of implementing Lean-Green with I4.0, and the dimensions and characteristics of Lean-Green 4.0, were researched. Table 4 lists the screened articles related to Lean-Green 4.0.

Table 4. Final list of screened articles related to Lean-Green 4.0 from the SLR process.

Authors	Year	Title
(Afum et al. 2023)	2023	Lean production systems, social sustainability performance and green competitiveness: the mediating roles of green technology adoption and green product innovation
(Duarte 2023a)	2023	Lean-Green 4.0: A Starting Point for an Assessment Model
(Kaswan et al. 2023)	2023	Integrating Green Lean Six Sigma and Industry 4.0: a conceptual framework
(Letchumanan et al. 2022)	2022	Analysing the Factors Enabling Green Lean Six Sigma Implementation in the Industry 4.0 Era
(Mingaleva et al. 2022)	2022	Digitalization and Modernization of the Industrial Production Management System Based on Lean-Green Approach
(Queiroz, Alves Junior, and Costa Melo 2022)	2022	Digitalization as an Enabler to SMEs Implementing Lean-Green? A Systematic Review through the Topic Modelling Approach
(Zekhnini et al. 2022)	2022	A model integrating Lean and green practices for viable, sustainable, and digital supply chain performance
(Zhu et al. 2022)	2022	Research on Driving Factors of Collaborative Integration Implementation of Lean-Green Manufacturing System with Industry 4.0 Based on Fuzzy AHP-DEMATEL-ISM: From the Perspective of Enterprise Stakeholders
(Ganjavi and Fazlollahtabar 2023)	2021	Integrated Sustainable Production Value Measurement Model Based on Lean and Six Sigma in Industry 4.0 Context
(Dahmani et al. 2021)	2021	Smart circular product design strategies towards eco-effective production systems: A Lean eco-design Industry 4.0 framework
(De Giovanni and Cariola 2021)	2021	Process innovation through industry 4.0 technologies, Lean practices and green supply chains
(Ghaithan et al. 2021)	2021	Impact of Industry 4.0 and Lean Manufacturing on the Sustainability Performance of Plastic and Petrochemical Organizations in Saudi Arabia
(John, Sampayo, and Peças 2021)	2021	Lean & Green on Industry 4.0 Context – Contribution to Understanding L&G Drivers and Design Principles
(Touriki et al. 2021)	2021	An integrated smart, green, resilient, and Lean manufacturing framework: A literature review and future research directions
(Tripathi et al. 2021)	2021	An innovative, agile model of smart, Lean–green approach for sustainability enhancement in industry 4.0
(Verma and Sharma 2021)	2021	An I4.0 review on Lean Green and Six Sigma based on energy parameter
(Wagire et al. 2021)	2021	Development of maturity model for assessing the implementation of Industry 4.0: learning from theory and practice
(Duarte et al. 2020)	2020	Business Model, Lean and green management and Industry 4.0: A conceptual relationship
(Kamble, Gunasekaran, and Dhone 2020)	2020	Industry 4.0 and Lean manufacturing practices for sustainable organizational performance in Indian manufacturing companies
(Leong et al. 2020)	2020	Enhancing the Adaptability: Lean and green strategy towards the Industry Revolution 4.0
(Titmarsh, Assad, and Harrison 2020)	2020	Contributions of Lean Six Sigma to sustainable manufacturing requirements: An Industry 4.0 Perspective
(Yadav et al. 2020)	2020	A framework to overcome sustainable supply chain challenges through solution measures of industry 4.0 and circular economy: An automotive case.
(Nascimento et al. 2019)	2019	Exploring Industry 4.0 Technologies to enable circular economy practices in a manufacturing context A business model proposal
(Varela et al. 2019)	2019	Evaluation of the Relation between Lean Manufacturing, Industry 4.0, and Sustainability
(Duarte and Cruz-Machado 2018)	2018	Exploring Linkages Between Lean and Green Supply Chain and the Industry 4.0
(Mayr et al. 2018)	2018	Lean 4.0 – A conceptual conjunction of Lean Management and Industry 4.0
(Duarte and Cruz Machado 2017b)	2017	An Investigation of Lean and green supply chain in Industry 4.0
(Mittal et al. 2017)	2017	Adoption of Integrated Lean-Green-Agile Strategies for Modern Manufacturing Systems

Research gaps

The literature has limited research on integrating Lean-Green with I4.0, Lean with 4.0, Green, and Sustainability with I4.0. Thus, although the SLR in this study was specific to Lean-Green 4.0, the authors have endeavoured to review separate studies in Lean-Green and I4.0 to understand how they can be integrated. In addition, increasing research interest in Lean-Green 4.0 provides the impetus to conduct this research.

4. Results

4.1. Literature results & analysis related to Lean, Green & I4.0

Of the 13 journals selected, 4 contributed to 43% of the final screened collection or 57% of the final screened journal selection as they had published more on the Lean, Green & Sustainability research theme than others. For example, Sustainability and the Journal of Cleaner Production had each published 19% (4 articles) of each of the final journal selections, with the Journal of Manufacturing Technology Management and the International Journal of Production Research each contributing 10% (these 2 journals had published 2 papers each) (Figure 2).

Figure 2. The top 4 journals publishing in the area of Lean-Green 4.0.

The area or theme of Lean, Green and Sustainability is new in the literature. The inclusion years for this research theme were from 2013 to 2023. However, the research team has only started to appear since 2017, with a peak of 9 papers in 2021. Considering the Lean Green theme only emerged in the mid-2000s (Antony et al. 2022) and the Industry 4.0 theme in the mid-2010s (McDermott et al. 2022) -it is not surprising to see Lean Green 4.0 only appearing recently in the literature. Conference papers have maintained a very inconsequential output of, on average, 1-2 papers a year since 2017, with journal papers driving 75% of the publications related to the theme. At the time of writing, 3 papers related to the themes were published in 2023 (Figure 3).

Figure 3. Publication trends on the theme of Lean, Green & Sustainability.

In an examination of the final 28 selected articles, the most published authors in the area are Susana Duarte (4 papers) and her co-author Prof Cruz-Machado (3 papers), both of the Universidade NOVA de Lisboa in Portugal, followed by Professor Sachin Kamble of EDHEC Business School in France (3 papers) and Professor Jose Garza-Reyes (2 papers) of the University of Derby in England. Professor Jose Garza Reyes of the University of Derby in the United Kingdom also frequently appeared in the literature concerning Lean-Green and Sustainability.

4.2. Lean-Green 4.0 defined

A Lean-Green management system can be an enabler and accelerator for I4.0 implementation (Duarte and Cruz-Machado 2018). Technological enhancements and smart technology tools such as the internet of things, additive manufacturing, cloud-based technologies, collaborative robots, artificial intelligence, and big data analytics enable an increased understanding of the wants and needs of customers and enable more Lean-green processes and relationships (De Giovanni and Cariola 2021),(Duarte and Cruz-Machado 2018); (Ibarra, Ganzarain, and Igartua 2018); (Ghaithan et al. 2021); (Dahmani et al. 2021). Indeed, smart, lean, and green are three corresponding approaches because of the similar waste reduction goals with efficient utilization of resources (Tripathi et al. 2021). Mayr et al. (2018) described the integration of Lean and I4.0 and how Lean enabling I4.0 introduction. Conversely, I4.0 tools enhance Lean manufacturing with complementary relationships between the two (Ghaithan et al. 2021). Also, Queiroz, Alves Junior, and Costa Melo (2022) reinforce that digitalization is an enabler to Lean and to Lean-Green in Small and Medium-sized Enterprises (SMEs).

Government incentives are very significant to a successful Lean-Green active promotion and implementation in SMEs, according to Zhu et al. (2022). Similarly, SMEs have highlighted the need for government support for I4.0 implementation (Nelson et al. 2022). Many manufacturers are discouraged from implementing I4.0 due to the lack of system and technology support (Leong et al. 2020).

As with any strategic implementation, it is important to have a clear strategy for Lean-green 4.0 supported by the leadership (Duarte 2023a; Leong et al. 2020). Employees’ skills and qualifications, training in digitalization, data analytics and problem-solving, and clear communication of change are also critical to Lean-Green 4.0 implementation (Duarte et al. 2020; Verrier, Rose, and Caillaud 2016; Zhu et al. 2022). Ghaithan et al. (2021) analyse the integrated influence of I4.0 technologies and lean manufacturing on sustainability performance, in their study.

4.3. Benefits of integrating Lean, Green & Sustainability

Lean concepts for minimizing waste generated in operations and green concepts relevant to all three aspects: economic, environmental, and social; sustainable logistics practices can be integrated with digitalization to become Lean-green 4.0 (Edirisuriya, Weerabahu, and Wickramarachchi 2018; Kaswan et al. 2023). Antony et al. (2022), in their study on the evolution of Lean 4.0, described the Lean and Green integration in the early 2000s as the second evolution of Lean following the integration of Lean with Six Sigma. However, Lean 4.0 as a research theme is still nascent. According to Letchumanan et al. (2022) Lean-Green is a highly effective approach for doing operations more ecofriendly and promotes high product quality through the reduction of waste, emissions, and reworking, while respecting people. However, Lean-Green as a theme have only taken off from 2006 onwards (Garza-Reyes 2015). According to Varela et al. (2019), Lean positively influences the three main aspects of Sustainability: economic, environmental, and social. For example, Lean increases profit and decreases operational costs (economic dimension), decreases industrial waste and increases the practice of circular economy (environmental dimension), and increases the participation of the employees in decision-making or decreases working accidents (social dimension) (Varela et al. 2019). Indeed, Lean and I4.0 technologies have a positive relationship with developing the environmental dimension of Sustainability (Ghaithan et al. 2021; Varela et al. 2019). Recently, Dahmani et al. (2021) relative to their study state ‘lean design combined with eco-design and Industry 4.0 represents an innovative model to include sustainability throughout the product life cycle’.

4.4. Challenges of integrating Lean Green & Sustainability

There is no unique way to implement Lean-Green practices (Duarte et al. 2020) and implement the requirements of I4.0 (Ibarra, Ganzarain, and Igartua 2018). The literature is still sparse in relation to the challenges of implementing Lean-Green 4.0, although much has been written on Lean-Green and I4.0 as separate topics. Also, the analysis through Sustainability is not well established. It is quite difficult to choose the criteria to characterize and assess the degree of Sustainability in each organization (Varela et al. 2019). Ghaithan et al. (2021) consider that more efforts are needed to develop Sustainability. Lean-Green practices are applied to eliminate challenges and problems to achieve Sustainability. One of these challenges is industrial waste, and the integration of Lean-Green helps to successfully eliminate this waste enhancing industrial sustainability (Tripathi et al. 2021). The objective of the organizations is to maximize economic benefits and raise social welfare while trying to reduce their environmental impacts. The managers can select the important criteria to manage in line with the outcomes. It is a crucial point because it will allow us to choose how to apply Lean-Green 4.0 practices.

4.5. Integrating Lean-Green 4.0 & other themes

There is not only one way to implement Lean-Green in the 4.0 scenario. This implementation, even only a transition to I4.0 scenario can be made in line with other themes/approaches. These are identified in the SLR different approaches as the methodology six sigma (Ganjavi and Fazlollahtabar 2023; Kaswan et al. 2023; Letchumanan et al. 2022; Verma and Sharma 2021 and Titmarsh, Assad, and Harrison 2020) the paradigms such as resilient (Touriki et al. 2021), agile (Mittal et al. 2018) and Sustainability. Table 5 presented the contributions of these studies. This will help to understand that Lean-Green are a really balanced and integrated approach due can be integrated with other themes.

Table 5. The contributions to other integrated themes.

Article	Integrated Theme	Contributions
Kaswan et al. 2023	Six Sigma	To propose a conceptual framework integrating Lean-Green-Six Sigma-Industry 4.0 approach The application of different tools and techniques at different stages of the realization of a project are enumerated.
Letchumanan et al. 2022;	Six Sigma	To identify and examine the enabling factors for the Green-Lean Six sigma implementation in the Industry 4.0 era. A structural model to conceptualize and operationalize this business strategy is created. The implemented methodological approach includes in a first step a systematic review of leading studies on the topic, and then the use of varimax rotation to analysis the principal factor.
Ganjavi and Fazlollahtabar 2023	Six Sigma	To develop a Sustainable Industry 4.0 Production Value Measurement Model Based on Lean and Six Sigma. To collect the Lean Six Sigma elements a survey is conducted, and the outcome is inserted into a Delphi framework. After an interpretive structural modelling (ISM) technique is adapted to map elements of lean six sigma and sustainability factors and indices.
Verma and Sharma 2021	Six Sigma	To examine the compatibility of the Lean, Green and Six Sigma concepts. A literature review was made to discuss the possible limitations/merits of Lean-Green six sigma (considered as an integrated approach).
Titmarsh, Assad, and Harrison 2020	Six Sigma and sustainability	To proposes a framework of using lean six sigma to achieve the sustainable manufacturing requirements from the perspective of Industry 4.0. A case study is used to investigate the effectiveness of the proposed approach.
Touriki et al. 2021	Resilient	To propose two research frameworks to guide academics and practitioners into a combination of the four paradigms of smart lean, green, and resilient in the manufacturing realm. A compilation on recent evolutions using a literature review was made, combining these four paradigms.
Mittal et al. 2018	Agile	To propose a framework of Lean Green Agile Manufacturing System developed to integrate lean, green, and agile approaches, addressing the three dimensions of sustainability, economic, societal and environmental. An identification of 10 enablers through a review of literature and discussion with experts in the industry and academia was developed.

5. Discussion

• RQ1: Review the literature to ascertain the characteristics of Lean Green and digitalization and review the current state of this area as a theme

This study found limited research on the theme of Lean-Green 4.0. It is still an evolving and nascent area. However, as mentioned previously, similar studies about Lean integration with Industry 4.0 (Zulfiqar et al. 2023), Lean-Green 4.0 (Kaswan et al. 2023), and Lean Six Sigma 4.0 (Antony et al. 2021) have concluded that there is a synergistic and symbiotic effect of Lean and Industry 4.0. Industry 4.0 aids the enhancement of Lean, Green, Six Sigma, and the Lean Supply Chain while having a Lean process aids I4.0 implementation (Kamble, Gunasekaran, and Dhone 2020).

However, the area is still emerging as a theme in the literature as there are still many unknowns about Industry 4.0 integration into organizations (Sony and Naik 2020).

• RQ2: Propose a model for a Lean-Green management system in the I4.0 environment to evaluate that transition.

Much literature discusses the integration of Lean and I4.0. The integration of Lean-Green and I4.0 has also been studied by many authors (Duarte et al. 2020; Duarte and Cruz-Machado 2018; John, Sampayo, and Peças 2021; Leong et al. 2020; Munoz-Villamizar and Santos 2021). Duarte and Cruz-Machado (2018) have studied the relationship between Lean-Green and Industry 4.0 through application across organizations in the entire supply chain. John, Sampayo, and Peças (2021) proposed a conceptual framework for a Lean-Green 4.0 integrated approach. This integrated approach demonstrated the relationship between the principles of Lean-green with I4.0 technologies and processes. Leong et al. (2020) model for a Lean-Green model to solve industry problems associated with I4.0 defined a checklist as a guide to identify key measurement indicators. De Giovanni and Cariola (2021) studied the impact of a process innovation strategy on lean and green practices through the implementation of digital tools, considering a particular strategy, the collaboration with suppliers. In their framework Dahmani et al. (2021) proposed strategies as for example, value focus, knowledge focus, continuous improvement culture, the use of digital tools, or strategies as reuse, reduce or recycling and disassemble. In the manufacturing context, Tripathi et al. (2021) proposed a model for smart Lean-Green implementation considering five different criteria: standard policy, optimum path planning, downtime, multi-skill and environmental impacts. Kaswan et al. (2023) examined the applicability of different tools and principles of Lean-Green and I4.0 at different stages of a Lean-Green and I4.0 problem-solving framework. Letchumanan et al. (2022) considered several important items and they can be distributed from strategic point of view (e.g. linking Lean-Green six sigma to organizational vision/mission statements and organizational readiness for Lean-Green six sigma implementation); from the tactical point of view (e.g. culture and supportive ambiance and companies’ reputation) and from an operational point of view (e.g. employee involvement and empowerment and teamwork) in a total of 27 enablers.

Based on the research literature review and the SLR the Lean-Green 4.0 theory was collected and evaluated, and the dimensions for the framework were proposed to measure a Lean-Green 4.0 implementation (Figure 4). These assessment models demonstrate how organizations can be evaluated and indicate where improvement actions are needed.

Figure 4. The proposed dimensions to assign to the conceptual framework.

For the proposed model and based on critical success factors for Lean-Green and I4.0 identified from the literature, eight different dimensions were consolidated, namely: ‘leadership and strategy’, ‘people’, ‘process’, ‘product’, ‘customer’, ‘supplier’, ‘governance’, and ‘technology’. Such consolidation will be the basis for establishing the linkages between Lean-Green management and the I4.0 approach. Each dimension will result in several items to evaluate the organization’s current state. Table 6 provides examples of items that can measure the state of organizations in terms of Lean-Green 4.0.

Table 6. Dimensions and measurement items for Lean-Green 4.0.

Lean-green 4.0 dimension	Measurement item	Ref.
Leadership and strategy	Leadership with transparency in the communication Virtual leadership only when it is possible Management competencies Company’s digital transformation vision and roadmap / organizational vision/mission statements Company with a flat hierarchy Increased Profit New business models Participation of its employees in decision-making	(Duarte 2023a; Ghaithan et al. 2021; Helming et al. 2019; Leong et al. 2020; Letchumanan et al. 2022; Schumacher, Erol, and Sihn 2016; Varela et al. 2019)
People	Employees’ skills and qualifications Employee training Employee openness to digital transformation Systematic problem-solving to improve digital transformation Workplace safety	(Duarte 2023a; Duarte and Cruz Machado 2017a; Ghaithan et al. 2021; Ibarra, Ganzarain, and Igartua 2018; Kaswan et al. 2023; Letchumanan et al. 2022; Ramos et al. 2018; Verrier, Rose, and Caillaud 2016)
Product	Product individualization considering eco-design Innovation focus Control of resource usage Digitalization of products to integrate with other systems	(Duarte 2023a; Duarte and Cruz Machado 2017a; Duarte and Cruz-Machado 2018; Helming et al. 2019; Ibarra, Ganzarain, and Igartua 2018; Letchumanan et al. 2022; Mayr et al. 2018; Ramos et al. 2018)
Process	Waste elimination and control Environmental conscious design Flexible workforce Real-time monitoring and control Digital information process Process Technology Use resources more efficiently Value creation	(Duarte 2023a; Duarte and Cruz Machado 2017a; Duarte and Cruz-Machado 2018; Helming et al. 2019; Kaswan et al. 2023; Letchumanan et al. 2022; Ramos et al. 2018; Schumacher, Erol, and Sihn 2016, Schumacher, Nemeth, and Sihn 2019; Varela et al. 2019)
Customer	Digital channels Customer focus/needs Long-term relationship	(Duarte 2023a; Duarte et al. 2020; 2020; Duarte and Cruz Machado 2017a; Ibarra, Ganzarain, and Igartua 2018; Letchumanan et al. 2022)
Supplier	Digital channels Cross-company collaboration Sharing uncertainty Knowledge sharing Follow good environmental practices	(Duarte 2023a; Duarte et al. 2020; Duarte and Cruz Machado 2017a; 2017b; Ibarra, Ganzarain, and Igartua 2018; Letchumanan et al. 2022; Schumacher, Erol, and Sihn 2016)
Technology	Information technology resources Information technology integration More transparent information sharing Digital tools Equipment and Technology up-gradation. Technological readiness for implementation	(Duarte 2023a; Ibarra, Ganzarain, and Igartua 2018; Leong et al. 2020; Letchumanan et al. 2022)
Governance	Legal Requirements Technological standards Management Standards Perception regarding the usefulness of I4.0 Environmental impact	(Duarte 2023a; Duarte, Cabrita, and Cruz-Machado 2019; Duarte and Cruz Machado 2017a, 2017b; Duarte and Cruz-Machado 2018; Leong et al. 2020; Letchumanan et al. 2022; Schumacher, Erol, and Sihn 2016, Schumacher, Nemeth, and Sihn 2019)

5.1. Limitations of this study

The proposed framework is a starting point for the design of a model for the assessment of Lean-Green 4.0; This study contributes with valuable insights which dimensions and measurement items for Lean-Green 4.0 should be considered for the transition of Lean-Green strategy on I4.0 scenario. It theoretically identified and clarified the dimensions. Thus, this study needs to be tested, validated and deployed. Furthermore, this model should be developed to assess the organization’s development systematically. Also, this area is nascent in the literature, and there is particularly a shortage of practical case studies.

5.2. Theoretical & managerial implications

This study bridges the gap between academia and practice by providing valuable insights to guide leaders in their journey to agile transformation. The findings provide new knowledge to leaders and academics concerning the most critical factors for a successful transformation. Management can adapt their organizations by knowing how to execute a Lean-Green system in the new digitalization era. This will help evaluate the transition/implementation, reflecting on what strategies, action plans, and improvements must be applied. So, this model is intended to allow rigour in the transition process. This research aims to contribute to discussing the relationships between these two subjects.

6. Conclusion

The framework put forward in this study is a start for designing a model to assess and aid the implementation of Lean-Green characteristics and items within an Industry 4.0 environment. First, the dimensions of Lean-Green and the measurement criteria are identified as part of the model. Eight dimensions are put forward as part of the model, which are 1. leadership and strategy, 2. people, 3. Process, 4. Customer, 5. Supplier, 6. Governance, 7. product and 8. technology. The aforementioned dimensions are the foundation for connecting the various components of Lean-Green management with the I4.0 approach. Following studies of Duarte (2023a, 2023b), Schumacher, Erol, and Sihn (2016), Duarte et al. (2020), Wagire et al. 2021), this model should integrate the different weighting criteria for each dimension and the relevant measurement items.

This study contributes to the state of the art in relation to Lean-Green 4.0 integration and can be expanded and piloted in future research studies. The model should present the new guidelines and weighting criteria to evaluate the transition level. Future research is needed to test the model on organizations’ readiness. More criteria or measurement items can be integrated, and the weightings of the different dimensions and measurement items may be reviewed and edited. Implementing more case studies to deploy the model in different organizations and sectors will aid the validation of the model.

Acknowledgement

The authors acknowledge Fundação para a Ciência e a Tecnologia (FCT – MCTES) for its financial support for the research via the project UIDB/00667/2020 (UNIDEMI) part of which was initially presented at the 8th European Lean Educators conference in the University of Galway in Ireland in November 2023.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Susana Duarte

Dr. Susana Duarte holds a Ph.D. in Industrial Engineering. Presently she is an Assistant Professor in the Department of Mechanical and Industrial Engineering at NOVA School of Science and Technology, Universidade Nova de Lisboa (FCT NOVA), Portugal. She lectures several courses on topics related to industrial engineering including, production management, industrial strategy, and management, introduction to industrial engineering, logistics, quality management, decision models, among others. She is a research member of the Research and Development Unit for Mechanical and Industrial Engineering (UNIDEMI) where develops their investigation in the area of lean management, green management, supply chain management, performance measurement systems, and Industry 4.0. She made part of the research team of the project entitled ‘Lean, Agile, Resilient and Green Supply Chain Management’ and she has published scientific papers in several international refereed journals and international conferences proceedings. She was awarded Excellence Award from Emerald Group Publishing and four awards from International Conferences. She is a member of the board of the IPEI (Portuguese Institute of Industrial Engineering).

Olivia Mc Dermott

Dr. Olivia McDermott is an Associate Professor in Operational Excellence at the University of Galway in Ireland. She holds an MSc from the University of Galway in Quality & Reliability Engineering, an MBA from the University of Limerick and a D. Prof in Work Based Learning from the University of Middlesex. She completed her post-doctoral research on Lean Six Sigma in Healthcare at the University of Limerick. Prior to joining the University of Galway, she held several Senior Management positions in the Computer and Medical Device manufacturing industries and worked as a self-employed Operational Excellence consultant. She manages a large team of industry-based PhD researchers focused on Operational Excellence and Regulatory Affairs. She has published and co-authored over 100 peer-reviewed journal articles and conference papers, and she has hosted European and International Lean conferences at the University of Galway. She has received several awards for her published work, and she is on the Editorial Advisory board of the International Journal of Lean Six Sigma (IJLSS) and the Editorial Review Board of the TQM journal and the Technological Sustainability Journal.