The Role of Wastewater Recycling in Urban Water Management
By Jane Marsh
Urban wastewater management facilities are grappling with population growth and increasing wastewater. To address this, urban planners and engineers are adopting wastewater recycling to ensure public health, preserve the surrounding environment, and create city-wide resilience against future water scarcity.
What Is Urban Wastewater?
Urban wastewater is contaminated water from homes, businesses, and stormwater runoff. It flows throughout urban areas and is considered toxic to the environment and public health. City-based contaminant streams often include the following sources:
> Unpermitted or accidental dumping of effluents, including harsh chemicals and pharmaceuticals
> Industrial contaminant discharges from large facilities
> Sewage overflows after excessive precipitation
> Leaking from failed, clogged, and old sewer pipes
> Leaching from septic systems
> Authorized municipal wastewater discharges from wastewater treatment plants
Exposure to urban wastewater could result in severe illnesses with symptoms like diarrhea, vomiting, and cramping. Likewise, poor wastewater treatment and sanitation could contribute to the 700,000 people who die annually from drug-resistant diseases — a number expected to reach 10 million by 2050.
The Rising Demand for Wastewater Recycling
Amid rapid urbanization, wastewater increases pressure on municipal water treatment facilities and potable drinking water resources. As such, there has been a rising demand for wastewater recycling and reclamation.
Wastewater recycling removes harmful contaminants and bacteria from wastewater, allowing it to be used for agriculture, irrigation, industrial activities, groundwater replenishment, and ecological restoration projects. Some areas have explored reclaimed water to increase their drinking supplies, ensuring water security.
The water recycling market was valued at $16.1 billion in 2023 and is expected to reach $27 billion by 2028 — a 10.8% compound annual growth rate. In urban areas, this growth is primarily driven by climate change affecting water quality and the need for more robust treatment infrastructure.
Eventually, wastewater recycling in urban areas is intended to create a closed loop by turning nonpotable water into potable water. In 2015, San Francisco led this endeavor by requiring all new buildings over 100,000 square feet to include on-site wastewater recycling. By 2023, 25 greywater and six blackwater systems use these recycling mechanisms.
Greywater is derived from showers, tubs, and washing machines, while blackwater comes from dishwashers and toilets. Using recycled greywater to flush toilets and run a load of laundry could reduce new water consumption by 40%. If San Francisco approves using recycled water for showering, the potential to reduce another 20% exists.
In Atlanta, Georgia, Emory University recycles 400,000 gallons of wastewater on campus daily after installing its system in 2015. Meanwhile, North Carolina’s Cummins Rocky Mount Engine Plant can treat up to 75,000 gallons of wastewater daily for manufacturing activities.
Water Reclamation Technology and Methods
Engineers deploy various technologies and physical, biological, and chemical methods to recycle urban wastewater for reuse. One physical technique is adsorption, which removes foul-smelling dissolved organic compounds, often employing activated carbon, a common water filtration material.
Other processes use chlorine, peracetic acid, and ultraviolet (UV) radiation to disinfect water from bacteria. For example, in one study, researchers inactivated Escherichia coli after 60 minutes of UV exposure. Chlorine was just as effective after 120 minutes.
Water stripping is another method used to treat ammonia levels — most effectively between 20 and 100 milligrams per liter — and convert the ammonium hydroxide into a gas. The technique is relatively simple and doesn’t create a backflow of ammonia, which has environmental implications.
Of course, public drinking water treatment facilities require a multi-step method to ensure health and safety, including:
Coagulation: This step neutralizes dirt and dissolved particles by binding them with a chemical solution.
Flocculation: Adding more chemicals creates larger particles called flocs, which are easier to remove.
Sedimentation: This step separates solids from liquids — flocs settle at the bottom of the water.
Filtration: Filtering removes dissolved particles, solids, germs, bacteria, viruses and other contaminants.
Disinfection: The final step adds one or more chemicals to kill any remaining bacteria or parasites.
The Orange County Sanitation District and Water District in California recently completed the world’s most extensive wastewater purification system for potable water reuse. After starting the project in 2008, the agency achieved a capacity of 130 million gallons of high-quality drinking water daily in 2023.
Challenges and Future Trends
Wastewater recycling will continue to evolve as new technologies and techniques transform current processes. However, it faces numerous challenges.
According to one study, Europe and other countries demand nutrient recovery, like phosphorus from ashes or biochar from sludge. However, it isn’t yet a sustainable or cost-effective option. Nevertheless, automation and artificial intelligence tools will help urban wastewater management specialists detect contaminants and leaks early, especially in the coming decade.
Regulating bodies must also determine water-reuse standards for potable and nonpotable sources. Treatment facilitators have already endured the problematic removal of microplastics and micropollutants, including pharmaceuticals, cosmetics, and chemicals, which will require advanced treatment processes.
Getting the public on board with water recycling for drinking may be challenging, as perceptions may be negative. Although people might be more open to reusing recycled wastewater for irrigation or non-contact purposes, widespread acceptance for consumption or bathing could require convincing.
Wastewater Recycling Is the Future of Urban Living
Wastewater recycling presents opportunities to safeguard communities from water shortages, environmental damage, and public health crises. As developments continue to perfect treatment processes, reusing wastewater will become the norm, relieving facilities and natural resources from the increasing stress of urbanization.
Article by Jane Marsh
Jane works as an environmental and energy writer. She is also the founder and editor-in-chief of Environment.co