Overview of the RO Retrofit Project for Traditional Water Plants

Process Flow Framework of the Retrofit

graph LR
    A[Raw Water] --> B[Pre-treatment Retrofit Section]
    B --> C[RO Core Area]
    C --> D[Product Water Conditioning System]
    D --> E[Smart Water Supply Network]

    subgraph **Pre-treatment Retrofit Section**
        B1[Existing Sand Filter → Multi-layer Media Filter] --> B2[Added Ultrafiltration (UF) Membrane Group]
        B2 --> B3[Upgraded Activated Carbon Vessel]
    end

    subgraph **RO Core Area**
        C1[Primary RO Unit] -->|Brine| C2[Brine Energy Recovery]
        C1 -->|Product Water| C3[Secondary RO Unit]
        C2 --> C4[Brine Disposal Pool]
    end

Core Module Design of the Retrofit Scheme

Pre-treatment System Retrofit (Key Cost Reduction Point)

RO Core Process Design

Brine Treatment and Resource Reuse

• Brine Route: 25% of the primary RO brine → for plant greening water use (TDS within 2000 mg/L)
• High-salinity Disposal: 5% of the secondary RO brine, after electrochemical oxidation (current density 10 mA/cm²) → for disinfection and backflushing (replacing the original sodium hypochlorite addition)
• Crystallization Recovery: When calcium and magnesium ions > 500 mg/L, diverted to a fluidized bed crystallizer (recovery rate 90%)

Anti-fouling and Intelligent Management Technologies

Water Quality Comparison Before and After Retrofit (Key Indicators)

Implementation Steps of the Retrofit Project

Retrofit Project Schedule

Pre-treatment Retrofit

• Demolition of old filter media: a1, 2023-08-01, 3 days
• Installation of multi-layer filter: a2, after a1, 5 days
• Hoisting of ultrafiltration membrane group: a3, after a2, 7 days

RO System Installation

• Membrane rack foundation construction: b1, 2023-08-10, 5 days
• Pressure vessel assembly: b2, after b1, 4 days
• Pipeline welding and pressure testing: b3, after b2, 6 days

Commissioning and Operation

• Flushing of pre-treatment system: c1, 2023-08-25, 2 days
• Membrane flux testing: c2, after c1, 5 days
• 72-hour continuous operation: c3, after c2, 3 days

Economic Analysis (3000 m³/d Scale)

Key Retrofit Technology Points

1. Membrane Module Shock Resistance Design
   • 20% raw water bypass valve installed: automatically dilutes when influent COD > 10 mg/L
   • Membrane housing upgraded to SUS304 stainless steel (original UPVC withstands only 6 bar → upgraded to 16 bar)
2. Brine Resource Utilization Path
   • LR Brine →|TDS < 2000 mg/L| D[Greasing/Toilet Flushing] Brine →|Calcium and Magnesium > 300 mg/L| E[Fluidized Bed Crystallization → CaMg Granular Fertilizer] Brine →|Contains Disinfectant| F[Electrolytic Oxidation → Sodium Hypochlorite Solution (5%)]
3. Construction Obstacle Avoidance Principle
   • Utilize the structure of the siphon filter to install the UF membrane group (reduces height requirements)
   • RO high-pressure pump uses a co-base frequency conversion unit (vibration amplitude < 20 μm, no foundation modification required)
4. Operation and Maintenance Standard Upgrade
   • Cleaning Protocol: Acid cleaning every 3 months (pH 2 citric acid), Alkaline cleaning every 6 months (pH 12 Na₄EDTA)
   • Membrane Life Assurance: 72-hour trial operation of the pre-treatment system before installation to meet standards (SDI < 4, Fe < 0.05 ppm)