Feasibility Study on Greywater Reuse Technology: A Sustainable Water Solution

Greywater reuse refers to the process of treating and recycling domestic wastewater—such as water from showers, sinks, and laundry—for non-potable purposes like toilet flushing, landscaping, and vehicle washing. This reclaimed water, commonly referred to as “greywater,” has a quality that falls between fresh supply water and raw sewage. In regions facing freshwater scarcity and urban water supply challenges, greywater reuse technology offers a highly feasible, eco-friendly solution. It not only conserves precious water resources but also mitigates environmental pollution, making it a key focus in China’s long-term water management strategy.

Typical sources of greywater include:

• Shower and bath drainage
• Washbasin runoff
• Laundry wastewater
• Cooling water discharge
• Effluent from secondary clarifiers in municipal wastewater plants

Not recommended as greywater sources:

• Industrial wastewater
• Sewage from infectious disease hospitals or nuclear facilities
• Kitchen wastewater (due to high grease and organic content)
• Laundry discharge from large laundromats (unless pre-tested for detergent compatibility)

For residential buildings, all household wastewater except toilet discharge may be reused. In commercial or mixed-use buildings such as hotels and shopping centers, reuse is best limited to relatively clean sources like bath, shower, and washbasin water.

To ensure safe and efficient reuse, greywater must meet specific water quality standards:

Hygienic Safety:

• No harmful pathogens or toxic substances
• Measured by E. coli count, total bacterial count, BOD (Biochemical Oxygen Demand), COD (Chemical Oxygen Demand), and suspended solids

Aesthetic Acceptability:

• Clear appearance, no offensive odor
• Assessed by turbidity, color, surfactants, oil content

Corrosion & Maintenance Risk:

• Should not damage pipelines or create operational burdens
• Evaluated by pH, total hardness, and dissolved solids

Greywater treatment generally involves three main stages:

Pre-Treatment:

• Equipment: Bar screens, equalization tanks
• Purpose: Remove debris, stabilize inflow quality

Primary Treatment:

• Focus: Decomposition of organic pollutants
• Core technologies: Biological processes (aerobic or anaerobic)

Post-Treatment:

• Purpose: Disinfection and polishing
• Techniques: Filtration, chlorination, or UV disinfection to meet water reuse standards

There are three commonly used technologies in greywater reuse:

Biological Treatment:

• Most widely used
• Involves microbial degradation (aerobic and anaerobic processes)
• Cost-effective and environmentally friendly

Physicochemical Treatment:

• Combines coagulation, sedimentation (or flotation), and activated carbon adsorption
• Produces high-quality effluent but at a higher operational cost

Membrane Treatment:

• Uses ultrafiltration (UF), microfiltration (MF), or reverse osmosis (RO)
• Offers high removal efficiency and compact system design
• Challenges: Membrane fouling and cost

Factors to consider when selecting a treatment system:

• Quantity and quality of greywater
• Reuse requirements (e.g., toilet flushing, landscaping)
• Site-specific constraints (space, noise, odor)
• System reliability and ease of maintenance

Disinfection is essential in all processes, commonly done using chlorine-based agents.

Examples of Process Flow Designs:

For effluent from municipal sewage plants:
Source → Equalization Tank → Filtration → Disinfection → Storage → Reuse
For decentralized residential greywater:
Source → Hydraulic Screen → Equalization Tank → Biological Reactor → Filtration → Disinfection → Storage → Reuse
These systems can be designed as above-ground or underground, depending on the site conditions.

Modular systems integrate multiple treatment units into a compact setup, making them ideal for individual buildings or small communities (up to ~3,000 people or 1,500 m³/day). Key features:

• Space-saving, compact design
• High automation and minimal manual intervention
• Common components: pre-treatment, aerobic/anaerobic reactors, flotation units

The MBR combines biological degradation and membrane filtration in a single unit. Its advantages:

• Superior effluent quality
• Small footprint
• Easily automated and scalable

Membrane Contamination Concerns:
Despite the benefits, MBR systems face challenges with membrane fouling, primarily due to:

• Organic accumulation on the membrane surface
• Precipitation of inorganic materials
• Biofilm formation by microorganisms

Regular maintenance and pretreatment are crucial to mitigating fouling and ensuring consistent operation.

Greywater reuse technology is an essential innovation for sustainable urban development. By recycling domestic wastewater through advanced treatment systems, cities can significantly reduce their reliance on freshwater sources while minimizing pollution. With tailored system designs, proper water quality management, and modern equipment like MBR units, greywater reuse becomes a practical and effective strategy for residential buildings, commercial complexes, and even municipal infrastructure.

Xi’an CHIWATEC Water Treatment Technology is a high-tech enterprise specialized in various water processing devices. Aside from these individual products, which cover a number of types and series, we can also help with related comprehensive engineering projects. Thanks to our hard work and dedication upon our founding, we are now one of the fastest-developing water treatment equipment manufacturers in Western China.

Further reading

• The Role of Zinc Chloride and Phosphoric Acid in Water Treatment Chemicals for Closed Loop Systems
• Drinking Water Treatment Process Flow: A Comprehensive Guide to Water Purification
• Recirculating Aquaculture Water Treatment Technology: Enhancing Sustainability and Water Quality in Fish Farming