An integrated Lean Six Sigma and circular economy framework for enhancing the sustainable performance of a wastewater treatment plant

Purpose This research explores how integrating Lean Six Sigma (LSS) methodologies with Circular Economy (CE) principles can enhance operational efficiency and sustainability in wastewater treatment (WWT) systems. Design/methodology/approach Using a case study approach, this research evaluates a municipal WWT plant as a bounded system. It applies established tools, such as Failure Mode and Effects Analysis (FMEA), regression analysis and hypothesis testing, to assess process performance. While these tools are widely recognized, their domain-specific adaptation to climate resilience and CE challenges in WWT systems remains limited, particularly within a structured, single-case empirical framework. Findings The results show that traditional quality improvement tools can be effectively adapted to achieve environmental goals. The proposed framework achieved a 6.5% reduction in energy use in the secondary treatment stage, corresponding to annual savings of 575,665 kWh and approximately $48,891. It also contributed to reduced greenhouse gas (GHG) emissions by recovering methane (CH4) and supported long-term resilience through hydraulic capacity forecasting. Research limitations/implications Although based on a single case, the study offers insights that can guide broader application across WWT sectors and geographies, laying the groundwork for future empirical validation. Practical implications This research provides a flexible framework for industry professionals to integrate LSS and CE strategies into infrastructure operations. Originality/value The study bridges a research gap by introducing a novel LSS–CE framework tailored to sustainability and climate resilience in WWT systems.