I. Background of Joint Procurement: Emergency and Long-Term Needs In 2025, municipal sanitation departments across Haikou City and its subordinate districts (e.g., Meilan District, Qiongshan District) jointly launched the 'Procurement Project for Dongfeng’s New Sewage Treatment Vehicle' to address sewage treatment challenges in urban drainage networks, wastewater treatment plants, and concentrated areas such as farmers’ markets and catering zones. Located at the northern edge of the tropics, Haikou features a tropical maritime monsoon climate, with an annual average humidity exceeding 85% and a rainy season lasting up to six months. Frequent heavy rainfall places excessive load on sewage pipelines and accelerates odor emission. Conventional water-sprinkling trucks or vacuum suction trucks are inadequate for immediate treatment of high-concentration, high-solid-content sewage. In contrast, the new sewage treatment vehicle offers integrated functions — simultaneous suction and treatment, solid-liquid separation, and discharge meeting regulatory standards — making it an essential solution for emergency environmental protection. According to local procurement practices, the total budget for this joint procurement is capped at approximately RMB 4.507 million, with plans to procure eight units of the new Dongfeng-chassis sewage treatment vehicles, each priced at around RMB 500,000 (based on publicly available tender information). The project requires vehicles to feature corrosion resistance, high sealing integrity, and high-load continuous operation capability, with delivery and registration to be completed within 30 days after contract signing. II. Establishment of Unified Technical Standards: Addressing Three Key Challenges in Humid-Hot Environments Prior to tendering, Haikou’s municipal sanitation department organized multiple technical coordination meetings, with Chengli Special Purpose Vehicle Co., Ltd. (hereinafter referred to as 'Chengli') actively participating and providing technical recommendations. Based on Haikou’s local climate conditions and operational scenarios, the final technical specifications were focused on the following three critical aspects: 1. Anti-Rust Coating: Epoxy Zinc-Rich Primer + Polyurethane Topcoat Applied to All Critical Components Haikou’s high-temperature, high-humidity, and severe salt-fog environment necessitates robust corrosion protection. The specification mandates dual-layer anti-rust treatment — both internally and externally — for core components including sewage tanks, piping, pumps, and valves. Chengli’s Dongfeng-chassis sewage treatment vehicle (reference model CLW5180GSSD6 — originally a water-sprinkling truck chassis, adapted via targeted modifications for sewage treatment functionality) employs an epoxy zinc-rich primer with a minimum thickness of 80 μm, followed by a polyurethane topcoat, ensuring no large-scale rust formation within three years. Additionally, the interior tank surface is lined with corrosion-resistant fiberglass-reinforced plastic (FRP), capable of withstanding sewage media with pH values ranging from 4 to 9. 2. Sealing Component Durability under Humid-Hot Conditions: Fluoroelastomer (FKM) O-Rings and Mechanical Shaft Seals Conventional nitrile rubber (NBR) seals tend to age and deform rapidly under high-temperature, high-humidity conditions, leading to leakage. The tender technical documents explicitly require fluoroelastomer (FKM)-based sealing components — including O-rings and mechanical shaft seals — for all hydraulic lines, sewage pump bodies, manhole covers, and discharge valves. FKM exhibits superior temperature resistance (−20°C to +200°C), oil resistance, and acid/alkali resistance compared to standard rubber. Chengli comprehensively upgraded the sealing system across all supplied vehicles and introduced a dual-seal configuration (O-ring + mechanical seal), eliminating leakage risks even during continuous operation exceeding eight hours. 3. High-Loa