I. Case Background: Procurement Decision by a Municipal Sanitation Department in Changde City In Q3 2025, a municipal sanitation department in Changde City, Hunan Province (hereinafter referred to as the 'Procuring Entity') planned to procure a batch of blue-license-plate sewage treatment vehicles for sewage suction, discharge, and preliminary treatment in old urban residential communities, farmers' markets, and along small rivers. The project budget was approximately RMB 1.373 million, requiring a gross vehicle weight not exceeding 4.5 tons (eligible for Class C driver’s license), and self-priming/self-discharging functionality. Following open tendering, Chengli Special Purpose Vehicle Co., Ltd.’s Dongfeng D6 chassis-based blue-license-plate sewage treatment vehicle was awarded the contract, with a unit price of approx. RMB 112,000 (per publicly available tender information). The core challenge of this procurement was balancing daily operational capacity against vehicle maneuverability within a constrained budget. During preliminary research, the Procuring Entity evaluated three models—3-cubic-meter, 5-cubic-meter, and 8-cubic-meter units—and found that larger capacities impose stricter requirements on road width and turning radius. Moreover, due to chassis payload limitations inherent to blue-license-plate vehicles, maximum tank volume is typically capped at 6 cubic meters. Ultimately, the selected solution was a 5-cubic-meter sewage treatment vehicle built on the Dongfeng D6 chassis (model series corresponding to Chengli’s official announcement CLW5070GSSD6, etc.), equipped with automatic liquid-level control and high-pressure cleaning systems. II. Tank Capacity Selection Logic: How to Choose Among 3 m³ / 5 m³ / 8 m³ Models? When procuring sewage treatment vehicles for government use, tank capacity is the primary parameter—directly affecting single-trip efficiency and number of round trips required. Below are key selection criteria derived from Chengli’s product database and the specific requirements of this case: | Capacity Model | Applicable Scenarios | Chassis Platform | Single-Trip Capacity | Key Rationale | |----------------|----------------------|------------------|------------------------|----------------| | 3 m³ (Blue License Plate) | Old residential communities, narrow alleys, confined roads | Dongfeng D6 and other light-duty truck chassis | ~3 tons of sewage per trip | Excellent maneuverability; operable with Class C license; ideal for dense, point-source operations | | 5 m³ (Blue License Plate) | Farmers’ markets, medium/small rivers, municipal pipeline maintenance | Dongfeng D6, Foton Aoling, etc. | ~5 tons of sewage per trip | Best cost-efficiency balance—optimal integration of operational efficiency and maneuverability | | 8 m³ (Yellow License Plate) | Large industrial parks, main arterial roads, emergency response | Dongfeng Duolika, Sinotruk HOWO, etc. | ~8 tons of sewage per trip | Highest efficiency, but requires Class B license and faces restrictions on urban access | Selection Conclusion for This Case: As the Procuring Entity’s operational area consists primarily of inner-city roads—and most drivers hold only Class C licenses—the 8-m³ yellow-license-plate model was excluded outright. While the 3-m³ model offers superior agility, its limited per-trip capacity necessitates more frequent round trips, increasing fuel consumption and labor costs. The selected 5-m³ Dongfeng D6 model handles approximately 5 tons per trip, achieving a daily throughput of 40–60 tons (based on an 8-hour workday and an average cycle time—including travel to site, suction/discharge (~5–8 min), transport to discharge point, and return—of ~20 minutes per trip), perfectly meeting the Procuring Entity’s mandatory requirement of '50 tons per day' (per local procurement practice). III. Daily Operational Capacity Calculation Formula and Matching Table To assist the Procuring Entity in accurately assessing workload, Chengli’s after-sal