# Integrating Sustainable Performance into the Digital Maturity Models for SMEs in Manufacturing
## 3 Literature Review
### Sustainable Performance Measurement
#### 3.3.3 Environmental Performance  
The environmental responsibilities of manufacturing companies are increasing daily [6]. Consequently, the use of environmental indicators is becoming increasingly essential for SMMEs seeking to fulfil their environmental obligations. In this literature review, 22 authors employ environmental variables to evaluate companies' ecological performance. This section provides a synthesis of environmental indicators identified in the literature and explores three main categories: **resource usage**, **environmental impact**, and **product durability**. First, **resource usage** plays a fundamental role in environmental performance. Several studies highlight the positive impact of reduced consumption on the ecosystem. This part sheds light on the indicators used to assess **resource usage** in SMMEs, including **energy consumption**, **raw material usage**, and **water consumption**. Many researchers consider **energy consumption percentage** a relevant indicator for analysing environmental performance. This indicator is cited in 14 publications, including those by [52; 57]. The findings of [49] show that adopting Industry 4.0 technologies enables better energy load balancing, thus reducing energy consumption. Furthermore, ref. [66] emphasises the importance of the **primary type of energy used**, advocating for its inclusion in assessments. Additionally, 13 researchers, including [50; 52], stress the necessity of monitoring raw material usage. Seven studies, including [61], directly measure the **amount of raw materials consumed** to evaluate I4.0's impact on resource management. To refine this analysis, some authors, such as [59; 60], propose using the rejection rate, which reflects the **amount of wasted material** in production processes. Beyond quantity, the nature of raw materials is crucial for environmental impact. Hence, ref. [66] recommends evaluating the **amount of recycled raw materials** to better understand their effect. They note a recycling deficit in many industries, leading to significant waste. Not only are these materials not used to their full potential, but they also become unusable in other contexts, potentially having a significantly negative environmental impact. To quantify this issue, refs. [34; 65] advocate measuring **the percentage of non-reusable materials**. Regarding **water consumption**, several researchers, such as [54; 65; 63], consider this indicator, with [66] adding a parameter related to **water pollution levels** caused by production. Secondly, **environmental impact** is a key driver prompting companies to track their ecological performance. As indicated by [31], preserving ecosystems and improving human quality of life require adopting sustainable practices, including in the manufacturing sector. This subsection highlights commonly used indicators to assess the environmental repercussions of manufacturing SMMEs. The authors of articles in this literature review primarily use indicators related to **environmental repercussions** in an SMME to measure environmental performance. The indicators used primarily relate to **carbon emissions** and **ecological awareness levels**. Several studies examine how companies can evaluate their ecological footprint. Some authors, such as [55], suggest using the **level of environmental responsibility compliance** to assess SMMs' impact, an approach also shared by [46; 48]. Other studies focus on atmospheric emission levels. Eleven out of 28 publications consider air **emissions levels** to have a notable effect on ecological performance. Specifically, six authors, including [33; 36], propose measuring **greenhouse gas emissions** as an indicator, while ref. [51] recommends using the **carbon footprint**. The work of [54] underscores the importance of the energy transition for industrial performance and reducing the carbon footprint, using these indicators to measure the impact of digital technologies on pollutant emissions.