Greywater reuse as a key enabler for improving urban wastewater management

Sustainable water management is essential to guaranteeing access to safe water and addressing the challenges posed by climate change, urbanization, and population growth. In a typical household, greywater, which includes everything but toilet waste, constitutes 50e80% of daily wastewater gener-ation and is characterized by low organic strength and high volume. This can be an issue for large urban wastewater treatment plants designed for high-strength operations. Segregation of greywater at the source for decentralized wastewater treatment is therefore necessary for its proper management using separate treatment strategies. Greywater reuse may thus lead to increased resilience and adaptability of local water systems, reduction in transport costs, and achievement of fit-for-purpose reuse. After covering greywater characteristics, we present an overview of existing and upcoming technologies for greywater treatment. Biological treatment technologies, such as nature-based technologies, biofilm technologies, and membrane bioreactors (MBR), conjugate with physicochemical treatment methods, such as membrane filtration, sorption and ion exchange technologies, and ultraviolet (UV) disinfection, may be able to produce treated water within the allowable parameters for reuse. We also provide a novel way to tackle challenges like the demographic variance of greywater quality, lack of a legal framework for greywater management, monitoring and control systems, and the consumer perspective on greywater reuse. Finally, benefits, such as the potential water and energy savings and sustainable future of grey -water reuse in an urban context, are discussed.(c) 2023 The Authors. Published by Elsevier B.V. on behalf of Chinese Society for Environmental Sciences, Harbin Institute of Technology, Chinese Research Academy of Environmental Sciences. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Sustainable water management is crucial for ensuring access to safe water and addressing challenges such as climate change, urbanization, and population growth. Greywater, which accounts for 50-80% of daily wastewater generation in households and has low organic strength and high volume, requires separate treatment strategies due to its characteristics. Greywater reuse can enhance the resilience and adaptability of local water systems, reduce transport costs, and achieve fit-for-purpose reuse. Various biological and physicochemical treatment technologies can produce treated water suitable for reuse. Overcoming challenges such as greywater quality variance, legal framework, monitoring and control systems, and consumer perspective is important. The potential water and energy savings and sustainable future of greywater reuse in an urban context are also discussed.