I. Scenario Introduction: Practical Requirements of Ningbo Municipal Sanitation Department In 2025, a municipal sanitation department in Ningbo faced two major challenges in its regional drainage pipe cleaning and sewage treatment operations: (1) aging pipelines—severely clogged with sludge and debris due to prolonged disrepair, requiring frequent cleaning; and (2) the coastal high-humidity environment—accelerating corrosion of vehicle chassis and upper structures, thereby increasing failure rates of conventional models. After thorough evaluation, the department decided to procure a batch of National VI–compliant sewage treatment vehicles, prioritizing the Dongfeng 3308 mm wheelbase chassis (wheelbase: 3308 mm) for optimal maneuverability and load-carrying capacity. Through public tendering, Chengli Special Purpose Vehicle secured the contract, leveraging Dongfeng chassis factory-backed warranty, lifetime upper-structure service, and advanced anti-corrosion coating technology—delivering multiple units. This article analyzes the procurement case from perspectives including blue vs. yellow license plate classification, operational cost, technical specifications, and application scenarios. II. Blue License Plate (C-Class Driving License) vs. Yellow License Plate (B-Class Driving License): Core Selection Differences In sewage treatment vehicle procurement, driver qualification and vehicle specification are primary considerations. Below is a comparative analysis based on Chengli models (e.g., CLW5070GSSD6): Comparison Item Blue License Plate / C-Class License Solution Yellow License Plate / B-Class License Solution Typical Model Dongfeng 3308 mm wheelbase chassis (e.g., CLW5070GSSD6) Dongfeng or Sinotruk large-wheelbase chassis (e.g., CLW5180GSSD6) Driver Qualification C1 license sufficient—lowers driver recruitment threshold Requires B2 license—driver resources comparatively scarce Gross Vehicle Weight Approx. 7 tons (upper limit for blue plates) Approx. 18 tons (standard for yellow plates) Tank Capacity Approx. 3–5 m³ (typically 3–4 m³ for sewage treatment vehicles) Approx. 8–12 m³ (suitable for large-scale operations) Urban Accessibility Unrestricted in most cities; can access old residential communities and narrow roads Requires advance permit; access restricted in certain zones Annual Inspection & Commercial Operation Standard annual inspection; simple procedures Requires commercial operation permit; slightly higher inspection frequency Procurement Unit Price (Reference Public Tender Data) Approx. ¥98,000–¥120,000 (tax-inclusive landed price, per Chengli quotation) Approx. ¥140,000–¥180,000 (tax-inclusive landed price) In this Ningbo case, the procuring entity selected the blue-plate solution—given that most operational areas consist of urban branch roads and industrial parks, and the driver team predominantly holds C1 licenses—thereby reducing both operational costs and compliance risks. III. Operational Cost Differences: Real-World Considerations in Humid-Tropical Environments Ningbo lies along China’s coast, with an average annual humidity exceeding 80% and frequent rainy seasons (approx. 150 precipitation days per year). These conditions impose severe demands on the corrosion resistance and sealing component durability of sewage treatment vehicles. To address these challenges, Chengli Special Purpose Vehicle implemented the following measures in the upper structure: • Anti-Corrosion Coating: Tanks and piping systems are coated with epoxy resin anti-rust primer, followed by polyurethane topcoat—achieving salt fog resistance exceeding 500 hours, effectively countering coastal high-salinity corrosion. • Sealing Component Durability: Critical valves and pipe joints utilize fluorocarbon rubber O-rings, offering oil resistance and temperature tolerance from −20°C to 150°C—minimizing aging under humid-heat conditions and ensuring long-term sealing integrity. • Rainy-Season Operation Frequency: The vehicle is equipped with a h