To provide reliable water in a warming world, cities are testing small-scale treatment systems and wastewater recycling

Many things can go wrong in a large urban water system. Pump malfunction. The valves break. The pipes are leaking. Even when the system is working properly, water can remain in the pipes for long periods of time. Water scarcity is also a Growing problem in a warming worldas communities are discovering throughout the American Southwest and in many developing countries.

That’s why cities have begun experimenting with small-scale alternatives, including wastewater recycling and localized water treatment strategies known as decentralized or distributed systems.

Yo study water systems on a small and large scale, focusing on innovative system designs that enable local use of water sources that would otherwise be wasted. As technology improves, cities discover something that Rural communities have long known: Small scale water treatment, properly designedcan be cheaper and easier to maintain than a centralized system, and can improve water security and even the environment.

Clean water: lessons from nature

Almost all water has value and can be cleaned and used.

Nature makes a great job cleaning the water naturally as it flows through the ground. Soil physically filters water, and chemical and biological processes help remove contaminants over time.

Those processes can be imitated by water treatment plants and filters that are increasingly more effective.

Traditionally, cities have relied on centralized water systems that treat fresh water from a river or aquifer at a central facility and then distribute it through a large network of pipes. But that infrastructure becomes increasingly vulnerable to disruptions as it ages. And climate change, water scarcity and population growth are adding pressure on the system.

So some cities are experiencing with so-called distributed systems. These are small-scale water treatment, recovery and recycling plants that are designed to collect, treat and reuse water very close to both the source and the user. Some are separate operations. Others are connected to the larger system in a hybrid model.

For example, a decentralized system could treat wastewater in an urban area and recycle it for reuse within that area by the same users, such as El Paso, Texas, is doing. Or could collect stormwater runoff and wastewater from homes and redirect it specifically for irrigation or to recharge groundwateras Austin, Texasand San Francisco do.

An illustrated tour of how water treatment systems generally work.

Windhoek, Namibia, a city of about 430,000 people surrounded by an arid landscape, has been treating wastewater to an adequate consumption level and returning it to homes since 1968 for all types of uses, including cooking and drinking. Stormwater runoff, industrial water, wastewater, and even agricultural runoff It can be treated and recycled with modern technology. to become drinkable.

All of these approaches, whether connected to the main system or as separate closed systems, can reduce the community’s overall freshwater demand from rivers or aquifers.

Technology is making more water more reusable

Small-scale treatment can range from advanced filters within individual homes to tank treatments serving groups of homes or commercial, industrial and agricultural facilities.

Often, the treated water will non-potable uses such as toilet flushing or to replenish groundwater. But advances in technology They are making these decentralized water systems more viable and expanding their uses.

Electrochemical and membrane-based processes. have shown great potential to recover fresh water, nutrients (which can be used as fertilizer) and energy from wastewater. These processes include reverse osmosis, which pushes water through a semipermeable membrane to remove impurities, and electrodialysis, which uses an electric field.

Microbial fuel cells go a step further and use the microbes present in wastewater to produce electricity and facilitate wastewater treatment simultaneously. Another energy recovery method involves capturing biogas, primarily methane, from the decomposition of organic matter in wastewater in the absence of oxygen.

Unlike conventional treatment technologies, which operate on a large scale, these emerging treatment processes use modular designs that can be easily scaled up or down.

They can also be used to create hybrid systems by supplementing large centralized systems with treated water, particularly in arid regions where water supplies are scarce.

Water recycling in Windhoek, Namibia, where fresh water is scarce.

How a hybrid system could help Houston

To test how a hybrid system could help avoid water shortages due to system outages, my colleagues and I created a houston model, a city with 7,000 miles of pipelines and 2.2 million residents. We simulated the impact that different types of water outages can have on that large centralized water supply and how distributed sources could help reduce the impact.

Overall, we found that installing hybrid systems worked better at delivering water and preventing low flows throughout the city than the centralized system alone, particularly in areas where low water pressure is common.

The pressurized flow of reclaimed water could also limit the spread of contamination from sources such as a terrorist attack in the vicinity of the reclaimed water source.

Of course, that doesn’t mean new water sources are risk-free. Additional sources connecting to a large water system can also introduce new potential sources of contamination, so system design is important.

Several The factors determine how effective water distribution can be.. Population and building density, local water demand, soil characteristics, climatic conditions, infrastructure and the condition of existing water infrastructure play an important role. Research indicates that regions with high energy demands for water distribution, important local water needs and the ability to reuse wastewater they can earn more.

Notably, San Francisco has become a pioneer in extreme decentralization, with initiatives that extend down to the individual building level. In some buildings, water tanks, filters, and treatment in the basement cause water to Reusable for activities such as flushing toilets..

What’s getting in the way?

Despite the benefits, water reuse accounts for less than 1% of total water use in the US today.

Public perceptions about recycled water are a challenge, including enduring skepticism regarding safety, reliability and proper use of reclaimed water.

Properly recycled wastewater is considered safe to drink and may even contain less toxic risk than the water sources we already drink. However, water that is not treated to the proper level can pose significant risks to human health. TO robust business model It is also necessary to make decentralized systems profitable, along with a supportive governance structure.

As federal funds By investing efforts to revitalize America’s water infrastructure, American communities have a golden opportunity to strengthen their large water systems with a decentralized approach. Globally, as climate change fuels extreme storms and makes water supplies less reliable in many areas, small-scale decentralized systems could provide water security and increase access to water in areas that are currently underserved.

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