1. Overview of Reclaimed Water Reuse Systems
A reclaimed water reuse system uses domestic wastewater as a source and treats it through appropriate processes so that the resulting water can be reused for non-potable applications. The treated water, commonly referred to as reclaimed water, has a quality level between potable water and untreated wastewater. The technologies used to produce and reuse reclaimed water are collectively known as water reclamation and reuse technologies.
Treated reclaimed water can be used for a wide range of applications, including:
- Toilet flushing
- Landscape and garden irrigation
- Road cleaning
- Urban fountains and water features
- Other non-potable municipal applications
In regions where freshwater resources are scarce and municipal water supplies are insufficient, reclaimed water reuse can help conserve valuable freshwater resources while reducing the environmental impact of wastewater discharge. It is therefore an important approach to water pollution prevention and sustainable water resource management, as well as a water-saving technology with significant long-term application potential.
2. Reclaimed Water Treatment Methods
Current reclaimed water treatment technologies can generally be divided into three major categories.
2.1 Biological Treatment
Biological wastewater treatment utilizes microorganisms in water to adsorb, oxidize, and decompose organic pollutants in wastewater.
Biological treatment processes include both aerobic and anaerobic treatment, although aerobic biological treatment is more commonly used in reclaimed water applications.
2.2 Physicochemical Treatment
Physicochemical treatment typically combines coagulation and sedimentation or dissolved air flotation (DAF) with activated carbon adsorption.
Compared with conventional secondary wastewater treatment, physicochemical processes can further improve treated water quality. However, they may involve relatively higher operating costs due to chemical consumption, energy requirements, and adsorbent replacement.
2.3 Membrane Treatment
Membrane water treatment uses technologies such as ultrafiltration (UF), microfiltration (MF), and reverse osmosis (RO) to remove suspended solids, microorganisms, dissolved contaminants, and other impurities from wastewater.
One of the major advantages of membrane treatment is its high suspended solids (SS) removal efficiency. Membrane systems also require considerably less installation space than many conventional secondary wastewater treatment processes, making them particularly suitable for projects with limited available land.
3. Reclaimed Water Treatment Process Design
When designing a reclaimed water treatment process, the flow rate and quality of the influent wastewater, as well as the required reclaimed water quality and intended end use, should first be evaluated. Based on these conditions, an economical, reliable, and practical treatment process should be selected.
Several factors should be considered when determining the process configuration:
- Influent wastewater flow rate and water quality
- Required reclaimed water quality
- Intended reclaimed water application
- Equipment footprint and available installation space
- Surrounding environmental conditions
- Potential impacts of noise and odor
- Treatment system operating and maintenance costs
Organic matter is one of the principal contaminants in common reclaimed water sources. For this reason, biological treatment is widely used as the primary treatment process in many water reclamation systems.
Disinfection is also an essential step in the reclaimed water treatment process. Chlorine-based disinfectants are commonly used to control microorganisms and improve the microbiological safety of the treated water.
The overall treatment process depends largely on both the source of reclaimed water and its intended application. The wastewater source affects not only the selection of treatment technologies but also the total treatment cost. Selecting an appropriate reclaimed water source is therefore an important part of system design.
Domestic wastewater from residential communities is commonly used as a source for reclaimed water systems. After treatment, reclaimed water may be reused for landscape irrigation, toilet flushing, vehicle washing, and other non-potable purposes.
4. Reclaimed Water Quality Standards
Water quality requirements for reclaimed water reuse should be determined according to the intended application and the applicable national, industry, or local standards.
For different reclaimed water applications, the original text references the following standards:
- Landscape and ecological water applications: Water Quality Standard for Reclaimed Water Used for Scenic Water (CJ/T 95-2000)
- Domestic miscellaneous water applications: Water Quality Standard for Domestic Miscellaneous Water (CJ/T 48-1999)
- Industrial circulating cooling water applications: Code for Design of Industrial Recirculating Cooling Water Treatment (GB/T 50102-2003)
The applicable water quality requirements should be confirmed according to the project location, intended water use, and current regulatory requirements before system design and operation.
5. Reclaimed Water Treatment Process Flow
5.1 Treatment Process for Industrial Wastewater Discharge
When the treated effluent is intended primarily for compliant discharge, a typical process may be configured as follows:
Industrial Wastewater
↓
Equalization Tank
↓
Coagulation and Sedimentation
↓
Anaerobic Treatment
↓
MBR (Membrane Bioreactor)
↓
Effluent Discharge
This process combines physicochemical pretreatment, anaerobic biological treatment, and MBR membrane technology to reduce suspended solids, organic pollutants, and other contaminants before final discharge.
5.2 Treatment Process for Wastewater Reuse or Higher Effluent Quality Requirements
When the treated water is intended for reuse or must meet more stringent effluent quality requirements, an advanced membrane treatment process may be used:
Industrial Wastewater
↓
Equalization Tank
↓
Coagulation and Sedimentation
↓
Anaerobic Treatment
↓
MBR (Membrane Bioreactor)
↓
Cartridge Filter / Precision Filter
↓
Reverse Osmosis (RO) System
↓
Reclaimed Water Reuse
In this process, the MBR provides effective biological treatment and solid-liquid separation, while the downstream cartridge filtration and reverse osmosis system further remove fine particles and dissolved contaminants. The resulting high-quality reclaimed water can then be reused according to the requirements of the specific application.
Conclusion
A well-designed reclaimed water reuse system can transform domestic or industrial wastewater into a valuable alternative water resource. By combining biological treatment, physicochemical treatment, membrane filtration, MBR technology, and reverse osmosis, reclaimed water systems can reduce wastewater discharge, conserve freshwater resources, and support sustainable water management.
The optimal treatment process should always be selected according to the wastewater characteristics, required effluent quality, available installation space, operating costs, and intended reclaimed water application.