Who pays for urban cleanliness? Governance cost, behavioral nudge design, and informal recycling in Bangkok's waste regime

Cities in the Global South increasingly consider market-based instruments such as Pay-As-You-Throw (PAYT) to encourage source separation, improve municipal cost recovery, and support circular-economy transitions. However, the fiscal promise of PAYT depends not only on fee design but also on operational awareness, institutional trust, behavioral readiness, and the inclusion of actors already embedded in recycling systems. This study assesses municipal fiscal exposure under constrained implementation conditions rather than conducting an ex-post causal evaluation or predicting long-term household compliance. Using Bangkok's 2025 waste-fee reform as a case study, the paper develops an exploratory, scenario-based diagnostic framework that combines Material Flow Analysis (MFA), municipal cost data, and publicly released NIDA Poll evidence from 1310 Bangkok residents. The evidence reveals a substantial acceptance–readiness gap: while 73.97% of respondents supported behavior-differentiated waste fees in principle, 80.76% reported no awareness of the registration requirement for the reduced 20 THB/month fee, and 60.46% anticipated low or no local cooperation with the program. Under the model assumptions, a higher-separation pathway (S = 30%; BMA, 2026) is associated with approximately 2.13 billion THB in annual municipal cost savings. Under lower-compliance conditions, represented by a conservative 5–10% effective separation range, scenario-calculated savings are substantially lower, with potential burdens shifting toward municipal budgets, households, informal recyclers, and peri-urban environments. The study operationalizes this divergence as the scenario-calculated fiscal component of governance cost: the opportunity cost of unrealized efficiency potential under weak implementation readiness. The Bangkok case suggests that urban governance capacity functions as an economic input shaping the financial and environmental viability of price-based urban reforms.