Modelling the adoption of combined sewer overflow surveillance in Switzerland

During wet weather, combined sewer overflows (CSOs) spill untreated wastewater to hydraulically protect wastewater treatment plants. Interestingly, in Switzerland, the impact of these discharges on surface water quality remains unclear due to limited monitoring of CSO spills. Although affordable sensors and regular data review could address this, it is unclear why most wastewater associations seldom assess this data, highlighting political and organisational challenges within wastewater associations and their stakeholder networks rather than technical ones. This study explores different policy instruments to promote sensor adoption in CSOs, e.g. for event duration monitoring, using an agent-based model (ABM). The stakeholders' behaviour is modelled through the Theory of Planned Behaviour and the Bounded Confidence Model. We developed a prototype ABM, testing three policy instruments as scenarios: (i) professional events, (ii) mandatory sensor installation, and (iii) improved sensor technology. Our findings suggest that it is most effective to make sensor installation mandatory. However, quantitative results of the ABM must be taken with care, due to sparse data in regard to uncertainties, as emphasized by sensitivity analysis. Despite this, the process of building the model was considered beneficial, as it enhanced the understanding of the socio-technical system.