I. Procurement Background: Special-Vehicle Requirements in a Humid and Hot Environment. In 2025, a municipal sanitation department in Zunyi City planned to procure a batch of blue-plate sewage treatment vehicles for sewage suction, discharge, and emergency handling in old urban residential communities, farmers’ markets, and low-lying road sections. The procurement area is located in northern Guizhou Province, where summers are hot and rainy, with annual relative humidity consistently exceeding 80%. This imposes stringent requirements on the vehicle’s anti-corrosion performance, sealing component durability, and operational reliability under high-frequency usage. Per local procurement practice, the budget was capped at approximately RMB 278,000, with a gross vehicle weight not exceeding 4.5 tons—complying with the blue-plate C-class driving license requirement—and mandating essential equipment including a sewage tank, vacuum pump, self-priming/self-discharging system, and high-pressure cleaning unit. After preliminary screening, three suppliers advanced to the competitive bidding stage; among them, the Dongfeng D6 chassis-based sewage treatment vehicle recommended by Chengli Special Purpose Vehicle Co., Ltd. (hereinafter referred to as 'Chengli') became the primary candidate for evaluation. II. Competitive Bidding Process: Comparison of Quotations and Configurations Among Three Suppliers. Upon receiving multiple quotations, the procuring entity compiled a detailed comparative table. Key differentiators included chassis brand, superstructure manufacturing quality, anti-corrosion treatment, and after-sales service. Below are the critical comparison items (based on publicly available tender information): Comparison Item | Supplier A | Supplier B | Chengli (Winning Proposal) ---|---|---|--- Chassis Brand | Foton Time | JAC Junling | Dongfeng D6 Engine Model | Quanchai Q23-95E60 | Yunnan Diesel D20TCIF1 | Quanchai Q23-115E60 (China VI compliant) Tank Capacity | 3.5 m³ | 3.8 m³ | 4 m³ (official model number CLW5070GSSD6 corresponds to this chassis) Vacuum Pump Type | Standard water-ring pump | Rotary vane pump | Water-ring pump + wet/dry separation system Anti-Corrosion Treatment | Conventional paint coating | Phosphating + primer | Full-vehicle electrophoretic coating + epoxy coal-tar pitch anti-corrosion lining for tank Sealing Material | Standard rubber | Nitrile rubber (NBR) | Fluoroelastomer (FKM) — resistant to high temperature, oil, and humid heat Delivery Lead Time | 15–20 days | 20–25 days | 7–15 days (for standard models) Quoted Price (per unit, RMB 10,000) | ~21.8 | ~23.5 | ~22.5 (tax-inclusive landed price) After-Sales Service | 1-year warranty for chassis & superstructure | 2-year chassis / 1-year superstructure warranty | Nationwide Dongfeng chassis warranty + lifetime Chengli superstructure service As shown in the table, Supplier A offered the lowest quotation but featured weak anti-corrosion treatment and standard-grade sealing components—making it prone to rust and seal failure in Zunyi’s high-humidity environment. Supplier B quoted the highest price with only mid-tier specifications. Chengli’s quotation ranked mid-range, yet significantly outperformed competitors in anti-corrosion capability, sealing material quality, and after-sales support—and offered the shortest delivery lead time. III. In-Depth Configuration Analysis: Why Chengli’s Proposal Prevailed? 1. Anti-Corrosion Coating: Electrophoretic Coating + Epoxy Coal-Tar Pitch Lining. Due to Zunyi’s prolonged rainy season and high ambient humidity, sewage treatment vehicles are continuously exposed to wastewater and moist air. Chengli’s solution employs full-vehicle electrophoretic coating, supplemented by an internal epoxy coal-tar pitch anti-corrosion lining for the tank—a technique commonly used in chemical storage tanks, offering superior resistance to acid/alkali corrosion and rust formation. In contrast, Supplier A applied only conventional paint, which—