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The effects of population growth in the developing world and climate change have increased the stress on available water resources. The majority of Rajshahi city, Bangladesh, is facilitated with groundwater withdrawal. As Bangladesh is a country of monsoon climate, reserved rainwater can be contributed as an alternative to extracted groundwater. This study aims to develop a framework for rooftop rainwater harvesting (RRWH) for domestic purposes and estimate the appropriate size of the storage tanks and their costs required to fulfill the annual drinking and cooking water demands through RRWH in Rajshahi city of Bangladesh.

A total of 100 single-story residential dwellings with varying rooftop areas were surveyed for the projection of RRWH potential. The relationship between the size and cost of a water tank and the rooftop areas of different houses is expressed using a general mathematical equation. Cost estimates for the proposed RRWH system for all houses have been completed, and a cost model illustrating the relationship between rooftop or catchment area and associated cost of RRWH system has been developed.

This study reveals that a maximum of 110.75 m³/year rainwater can be collected from a 100 m² rooftop area of Rajshahi city. Moreover, this study finds that such harvesting of rainwater can reduce municipal water supply to the extent of almost 75%. Water samples collected from rooftops also revealed that if germs were removed through bacteria treatment, the collected rainwater potentially can be used for drinking and cooking purposes.

The novelty of this study is that it focused mainly on how significant RRWH can be to meet people’s daily required amount of water for household purpose and ascertain the cost reduction using the RWH method. This paper also is unique as it assessed the volume of the storage tank that is sufficient to distribute the necessary amount of water for drinking and cooking purpose as a sustainable alternative source in the dry season.

There is increasing interest in the connection between Industry 4.0 (I4.0) and operational excellence approaches; however, studies on the integration between Six Sigma (SS) and I4.0 have been absent from the literature. Integration with I4.0 technologies can maximize the positive effects of SS. The purpose of this study is to understand what types of relationships exist between SS and I4.0 and with I4.0's technologies, as well as the benefits derived from this integration and future directions for this field of study.

A Systematic Literature Review (SLR) was carried out to analyze studies about connections between I4.0 technologies and SS. SLR analyzed 59 articles from 2013 to 2021 extracted from the Web of Science and Scopus databases, including documents from journals and conferences.

The SLR identified relationships between SS and several I4.0 technologies, the most cited and with the greatest possibilities of relationships being Big Data/Big Data Analytics (BDA) and Internet of Things (IoT). Three main types of relationships were identified: (1) support of I4.0 technologies to SS; (2) assistance from the SS to the introduction of I4.0 technologies, and, to a lesser extent; (3) incompatibilities between SS and I4.0 technologies. The benefits are mainly related to availability of large data sets and real-time information, enabling better decision-making in less time.

In addition, the study can help managers to understand the integration relationships, which may encourage companies to adopt SS/Lean Six Sigma (LSS) in conjunction with I4.0 technologies. The results also drew attention to the incompatibilities between SS and I4.0 to anticipate potential barriers to implementation.

The study focuses on three previously unexplored subjects: the connection between SS and I4.0, the existing relationships with different technologies and the benefits resulting from the relationships. In addition, the study compiled and structured different types of relationships for SS and I4.0 and I4.0's technologies, identifying patterns and presenting evidence on how these relationships occur. Finally, exposes current trends and possible research directions.