Water Reuse System Design Process and Scheme for the Chemical Industry

The design of a water reuse system in the chemical industry revolves around selecting and integrating the most suitable treatment units based on different wastewater qualities and reuse requirements. The core goal is to ensure stable and compliant effluent quality while pursuing cost-effectiveness and operational reliability.

Here is a complete process framework for your reference.

🔍 Design Basis and Core Principles

First, establishing a solid foundation for the scheme is crucial.

• Source Water and Objectives: The design begins with a thorough analysis of the influent water quality (e.g., COD, hardness, heavy metals, salinity) and a clear definition of the reuse water standards (e.g., makeup water for cooling towers, boiler feedwater). This determines the complexity of the process train.

• Core Challenges: Chemical wastewater has a complex composition, potentially containing organics, hardness, heavy metals, and high salinity. Improper treatment can lead to membrane fouling, equipment scaling, and other issues.

• General Process Framework: A robust system typically follows the logic of "Pretreatment → Core Purification → Advanced Treatment and Reuse". The diagram below clearly illustrates this complete process and the connections between units.

🛠️ Detailed Explanation of Key Process Units

The main units are briefly explained below.

1. Pretreatment System

   • Equalization Tank: Its core function is to buffer flow fluctuations and homogenize water quality, creating stable conditions for subsequent treatment.

   • High-Efficiency Clarifier: Effectively removes suspended solids (SS), colloids, and some heavy metals through coagulation, flocculation, and sedimentation.

   • Multi-Media Filter: Employs filter media like quartz sand and anthracite for deep filtration, ensuring effluent turbidity meets standards.

   • Advanced Oxidation: For wastewater containing refractory organics or complexes, technologies like ozone-hydrogen peroxide (O₃/H₂O₂) can be used to "break complexes and chains", enhancing wastewater biodegradability and protecting downstream membrane systems.

2. Core Purification System

   • Ultrafiltration (UF): As a precise pretreatment for RO, UF can remove nearly 100% of bacteria, viruses, and most colloids. Its effluent quality meets the feed water requirements for RO systems (e.g., SDI ≤ 4). PVDF hollow fiber membranes with strong fouling resistance are recommended.

   • Reverse Osmosis (RO): The "desalination core" of the system, removing the vast majority of dissolved salts, small organic molecules, etc., with a typical salt rejection rate exceeding 97%. Select fouling-resistant membrane elements and design an appropriate recovery rate (e.g., 75%-80%).

3. Concentrate Treatment and Advanced Treatment

   • Concentrate Treatment: RO concentrate can be further concentrated using higher-pressure RO. For pursuing Zero Liquid Discharge (ZLD), end-stage technologies like evaporation/crystallization (e.g., MVR evaporator) are often employed to solidify dissolved solids into mixed salts, achieving complete wastewater solidification.

   • Ion Exchange and Disinfection: For extremely high water quality requirements (e.g., high-pressure boiler feedwater), mixed-bed ion exchange can be added after RO for deep desalination, supplemented by UV or sodium hypochlorite disinfection to ensure absolute product water safety.

⚙️ Key Points for Scheme Implementation

1. Prioritize Water Analysis: Comprehensive water quality analysis throughout the process is essential and forms the basis of all design.

2. Control Key Parameters: Strictly control the inlet/outlet indicators of each unit, such as the SDI value for UF, and the recovery rate and scaling potential for RO.

3. Automation Control: Implement PLC or DCS control systems for automatic chemical dosing, backwashing, and alarms to ensure stable system operation.

4. Professional Design and O&M: Such systems are highly specialized. It is recommended to commission an experienced water treatment engineering company for detailed design, installation, and commissioning, and to establish a professional operation and maintenance team.

I hope this framework provides a clear overview. If you can provide more specific influent water quality and reuse requirements, I can offer a more detailed analysis of process selection and parameter recommendations.