Overview of the Efficient Desalination Process for Municipal Water Supply

Process Flow Diagram

graph TB
    A[Water Source] --> B1[Pre-treatment Intelligent Grading]
    B1 --Low Conductivity Water--> C1[Submerged Ultrafiltration (UF)]
    B1 --High Conductivity Water--> C2[Selective Electrodialysis (ED)]
    C1 --> D[Nanofiltration (NF) Salt Separation]
    C2 --> D
    D --> E[Reverse Osmosis (RO) Fine Desalination]
    E --> F[Quality Adjustment and Disinfection]

    subgraph **Zero-Discharge Loop**
        D --> G1[ED Concentrate]
        E --> G2[RO Brine]
        G1 & G2 --> H[Vibration Membrane Crystallization (VMD)]
        H --> I[Crystallized Salt Resource Recovery]
    end

Innovative Design of Core Units

1. Pre-treatment Intelligent Grading System

2. Targeted Desalination Combined Process

3. Brine Zero-Discharge Module

Key Operating Parameters and Water Quality Improvement

Intelligent Control System

# Desalination System AI Optimization Algorithm
def ai_optimizer():
    if sensor.TDS > 300:  # High-salinity mode
        activate_ED(current_density=8mA/cm²)  # Activate electrodialysis
        set_NF_pressure(5.0bar)  # Increase nanofiltration pressure
    elif sensor.TOC > 2.0:  # Organic matter alert
        activate_carbon_bypass(flow=15%)  # Emergency activated carbon bypass
        reduce_RO_recovery(to=75%)  # Reduce RO recovery rate to prevent fouling
    # Crystallizer self-regulation
    if crystallizer.salt_purity < 97%:
        increase_VMD_temp(ΔT=5℃)  # Increase temperature for purification
        adjust_spray_rpm(+500rpm)  # Increase centrifugal speed

Investment and Operating Costs (50,000 m³/d Scale)

Three Phases of Engineering Implementation

1. Retrofit Adaptation Period (3 months)

gantt
    title Retrofit Progress Control

    section Facility Integration
    Demolition of old sand filter: done, 2023-09-01, 20d
    Installation of ED membrane rack: active, 2023-09-21, 35d

    section Pipeline Reconstruction
    Stainless steel pipeline welding: 2023-10-01, 40d
    Control system layout: 2023-10-20, 45d

2. Commissioning and Operation Period (Key Milestones)

• ED membrane stack activation: Pass 0.1 mol/L NaCl solution for 24 hours
• Flux ramp-up test: Gradually increase ED current density (5 → 8 → 12 mA/cm²)
• Brine crystallization verification: Continuous 72-hour operation to confirm salt purity > 98%

3. Intelligent Operation and Maintenance System

Summary of Core Innovations

1. Graded Desalination Strategy
   • Low-salinity water (TDS < 200 μS/cm) passes through UF + NF directly (skipping ED step)
   • High-salinity water undergoes ED for prior chloride removal → NF for sulfate retention → RO for fine purification
2. Energy Circulation Ecology
   • RO brine pressure → energy recovery → ED power supply
   • VMD steam residual heat → preheat raw water
   • Crystallizer centrifugal kinetic energy → self-power generation compensation
3. Added Value of Crystallized Products
   • Differential crystallization produces NaCl (industrial grade) + CaSO₄·2H₂O (food-grade gypsum)
   • For high-boron water sources (>0.5 mg/L), boracic acid (H₃BO₃ purity 99%) can be separated