Who Upgrades the Plant? A Tripartite Evolutionary Game Model for PPCPs Removal Technology Adoption

Pharmaceuticals and personal care products (PPCPs) contamination in aquatic environments has attracted considerable research attention, yet most studies focus on treatment technologies while the governance mechanisms coordinating stakeholder behavior remain underexplored. This study develops a tripartite evolutionary game model to analyze strategic interactions among pharmaceutical enterprises, wastewater treatment plants, and government environmental agencies in PPCPs pollution control. Replicator dynamics and stability analysis identify six stable equilibrium configurations and reveal that complete cooperation equilibrium cannot achieve asymptotic stability due to government fiscal incentives for regulatory withdrawal. Results demonstrate that technology-upgrading decisions of treatment plants respond primarily to government subsidies and penalties rather than upstream enterprise behavior. The mathematical finding that upstream enterprise production choices do not directly alter treatment plant upgrading incentives through cost transmission channels reveals that market-based coordination cannot spontaneously emerge without regulatory intervention, thereby strengthening the theoretical case for sustained government engagement. Sensitivity analysis indicates that reducing clean production costs and enhancing green product revenues accelerate system convergence toward environmentally favorable equilibria. Additional sensitivity analysis of treatment plant subsidy and penalty parameters confirms that both positive incentives and negative sanctions effectively promote technology adoption when appropriately calibrated. These findings provide theoretical guidance for designing differentiated policy instruments that balance market incentives with sustained regulatory oversight.