Flush with Care: Sustainable Waste Management at Arcosanti

by Alyssa Lutker, AmeriCorps VISTA

For The Cosanti Foundation, our mission to be “sustainably integrated with the natural world” means talking dirty. In other words, we have to talk about waste management. 

Two ways The Cosanti Foundation has tried to create a more sustainable waste management system include updating our toilets and utilization of a natural wastewater treatment system.

Although it is not a topic commonly discussed at the dinner table (or by most nonprofits), as both a residential and commercial location, Arcosanti is home to nearly 60 toilets, most of which feed into an on-site oxidation pond. Most of the buildings at Arcosanti were built decades ago, making many of the toilets on site just as old. As with any other technology, toilets have been improved with new, innovative technology and engineering to maximize their efficiency. 

Scott Riley, Cosanti Foundation’s Director of Site Management, explains “our older toilets used five gallons of water for a single flush, and that is an insane amount of water. New standard toilets have an improved efficiency that uses approximately 1.28 gallons of water for a single flush.”

Over the past several years, The Cosanti Foundation has worked to replace many of the toilets on site with newer and more efficient models. Conserving water is critical as we face a global water crisis, especially in the Arizona desert where water is more scarce. When many of the toilets were replaced, the most efficient toilets available flushed with 1.6 gallons, making those the most common on site. Any toilets replaced in recent years have been upgraded to the newest toilets that flush with only 1.28 gallons of water. 

Replacing toilets is not the only way we try to keep our waste management sustainable. 

At Arcosanti, 53 toilets of our 60 toilets feed into the site’s facultative oxidation pond. (There are another three toilets located “down the hill” in Arcosanti’s Camp which operate separately on a septic tank, similar to most residential systems.) This oxidation pond is a passive solar sewage system powered by microorganisms, such as bacteria and algae. Arcosanti’s oxidation pond is considered an iconic part of the site to most alumni, and a key example not just of our passive solar design, but of the “elegant frugality” approach to design that characterizes much of our architecture and infrastructure. And it works—at first glance, many visitors see a lush little pond in the desert, and have no idea what’s really going on beneath the surface.

Here’s the science:

When someone flushes a toilet, the black water (this is the term used to describe wastewater that must be treated as sewage) is taken by pipes to the oxidation pond. The anaerobic bacteria at the bottom of the pond break down the waste, allowing the byproducts to float to the surface. At the surface, aerobic bacteria uses oxygen to oxidize the waste byproduct, which releases CO2The algae growing on the surface of the pond completes the cycle by conducting photosynthesis. With energy from the abundant Arizona sunlight, the algae takes in the CO2 released, absorbs the carbon, and produces oxygen to continue to feed the aerobic bacteria. 

In a perfect world, that would be it: a self-sustaining sewage treatment solution. Of course, it’s not quite that simple. Over time, duckweed can grow to cover the surface of the oxidation pond. This interrupts the algae’s growth and restricts its access to sunlight, impeding the oxidation pond’s ability to naturally treat the wastewater. It has always fallen to Arcosanti residents and visiting alumni to periodically rake the duckweed off the oxidation pond’s surface. 

Mary Hoadley, an alumna of Arcosanti who was among those to help build our unique sewage system, has been raking the oxidation pond for over 40 years. 

“I love spending time there,” says Hoadley. “It has a nice little ecosystem. The cattails on the edge are great for transpiration. In the summer, there is lots of wildlife, such as birds, bugs, and frogs.”


Alumna Mary Hoadley stopped by to help clear the surface of Arcosanti’s oxidation pond.

Oxidation Pond First Flush on August 29, 1985. Photo courtesy of Russell Adams.










Recently, The Cosanti Foundation made the decision to develop the role of taking care of the oxidation pond into a paid position. Autumn Barger—an Arcosanti alumna and Arizona native—has recently filled that position. 

Barger took a workshop at Arcosanti in the summer of 2019 and then worked for a year at Cosanti in both the gallery and the shipping/packing department. Now, she splits her time between Scottsdale and Arcosanti, and has been volunteering in Arcosanti’s agriculture department for the past few months while she works towards an Associate of Applied Science in Agriculture Technology Management at Yavapai College. 

Excited to start her new job at the oxidation pond, Barger says “It makes me a little more grateful for our waste treatment system, and it is really zen and meditative.”


Autumn Barger is the Cosanti Foundation’s new oxidation pond caretaker.

For a few hours a week, you can find Autumn down at the oxidation pond, giving it TLC.


Waste management has a significant role in trying to live a sustainable lifestyle. As an urban laboratory intended to explore more sustainable ways of living, The Cosanti Foundation is dedicated to researching and trying out new technology that could lessen Arcosanti’s impact on the natural environment. 

The oxidation pond has served the site well for decades, and makes for a unique feature to explain to our daily tour groups. However, there is ongoing research being put into how (and where) to implement a more sustainable wastewater treatment system that would serve a growing population at Arcosanti and maximize resources by creating byproducts of bio-gas and treated greywater that can be reused.

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