Abstract
Biogas production within wastewater treatment plants (WWTPs) provides renewable energy recovery but also introduces complex process-safety challenges arising from the interplay of human, organisational, and technical factors. This study systematically evaluates how these dimensions interact to influence process-safety outcomes in UK wastewater-based biogas facilities, addressing a gap where prior safety research has largely prioritised the examination of technical and operational failures in the petrochemical and chemical sectors. A mixed-methods design was adopted, integrating a PRISMA-guided literature review, a structured national survey of industry professionals (n = 90), and analysis of historical incident reports (n = 63). Triangulated quantitative and qualitative data were examined using correlation and regression analyses to identify interdependencies among risk drivers. Findings reveal that gas-leak risk shows the strongest correlation with general site risks (r = 0.857, p < 0.001), followed by human and organisational factors (HOFs) (r = 0.768, p < 0.001) and process factors (r = 0.733, p < 0.001). The regression model (R-2 = 0.754) confirms that site-level governance (e.g., maintenance discipline, leadership visibility, and resource sufficiency) exerts the greatest influence on incident probability. These findings demonstrate that technical safeguards alone are insufficient without robust organisational and behavioural integration within Process Safety Management Systems (PSMS). The study demonstrates that HOFs directly shape safety outcomes in WWTPs, presenting a novel empirical contribution to literature, emphasising predictive maintenance, competence-based training, proactive reporting, and AI-enabled monitoring within PSMS as enablers of safer and more sustainable biogas recovery in wastewater operations.