Composting toilets in Arizona put waste to work


Arizona Sonora News

We Americans flush an average of 10 gallons of drinkable water down the toilet every day. That’s 3,650 gallons per person per year.

In Tucson, a year of flushing sends the equivalent of enough energy to power a 100-watt light bulb for between 450 and 5,550 hours (depending on the toilet and water source) spiraling down the toilet, according to Tucson-based Watershed Management Group. That’s because much of the water we flush down the toilet comes from the Central Arizona Project canal, which pumps water 320 miles uphill from Lake Havasu on the Colorado River to Phoenix and Tucson.

A group of composting toilet enthusiasts, local non-profits and University of Arizona researchers are collaborating to find a less wasteful way of dealing with our waste. Watershed Management Group is working with the Arizona Department of Environmental Quality to approve two home-built composting toilet designs for use in Arizona. If the designs are approved, Tucsonans will have a simple and cheap option to conserve water and energy, and enrich local soils.

A Simple Solution to a Complex Problem

One of the designs currently up for review was developed off the grid in Cascabel, a remote Southern Arizona community near Benson. Cascabel lies in the San Pedro River Valley. A strip of deep green vegetation follows the river up the middle of the valley, cutting through the muted sage-green of the surrounding desert. The Rincon Mountains rise to the west, separating the valley from Tucson. The whip-like arms of ocotillo prick the evening sky like spines on some strange sea star. The cool wind smells of creosote and dust.

The directions to David and Pearl Omicks’ place say to turn off the main dirt road onto a smaller one “marked by a small yellow sign that says ‘La Perla y El Burro’ (That’s Spanish for the Pearl and the Jack Ass. You can guess who’s who.)”

The home is tiny but beautiful in its simplicity. Inside is a bed, bookshelf, table for two and stove. David and Pearl designed and built the house themselves. It doesn’t have electricity, plumbing or a septic system.

That’s right. David and Pearl’s house doesn’t have plumbing or a septic system.

In fact, David hasn’t lived in a house with plumbing for more than 20 years. One day, when he was working as a maintenance man in an office building, everything seemed to go wrong with the plumbing. He realized he wanted to find a better way.

“I said, ‘You know, someday I’m going to build a house, and it’s not gonna have any plumbing,’” David said, grinning. “I don’t think I’ll ever go back.”

David and Pearl designed a simple composting toilet to replace a traditional flush toilet. The composting toilet doesn’t use any water or electricity, and it provides natural fertilizer for their small vegetable garden.

For David and Pearl, using a composting toilet is a way of “closing the loop.” Nutrients travel in a circular system from garden to table to toilet—and eventually back to the garden. They pick and eat vegetables from their garden, and when nature calls, they add a little bit of human waste to the composting toilet. That material goes through a lengthy composting process and is applied to their vegetable garden after about a year. Then the cycle begins again.

David has devoted his life to coming up with simple, nature-inspired solutions to complex problems, like how to deal with our waste.

“It’s what stirs my soul,” David said. “The whole idea of thinking in the way that nature works, cyclic thinking, in terms of life cycles and so forth, as opposed to the much more mechanized linear thinking, is just something that has always interested me.”

Before 2005, it was illegal to have a composting toilet in Arizona, even in rural areas, unless the soil on your property wasn’t suitable for a septic system, David said. In 2005 he worked with a group of “ad hoc composting toilet enthusiasts” to rewrite the Environmental Protection Agency’s policy. “We were primarily advocating rewriting the composting toilet section of the groundwater protection rules to be as encouraging to people who wanted to use composting toilets as possible,” David said.

Although commercially built composting toilets are now legal in Arizona, they cost between $1,200 and $6,000 to buy, permit and install, according to Watershed Management Group.  David’s composting toilet system is much cheaper— only $350 if made from new materials.

Conserving Water, Enriching Soil

In 2012, Watershed Management Group received an EPA Environmental Education Grant for desert soil stewardship. They used part of this grant to run a two-year composting toilet pilot program in Pima County. David’s composting toilet design was one of two tested at the 22 sites selected for the pilot program. Eight of those sites were the homes of composting toilet advocates, two were institutional (Watershed Management Group and the Community Food Bank of Southern Arizona’s Las Milpitas Farm) and the remaining 12 were residential.

Watershed Management Group inspected all the sites before and after installing toilets. Participants submitted self-monitoring forms, which were used to evaluate the program by University of Arizona researchers at the Bureau of Applied Research in Anthropology. The program ran from 2012 through 2014.

At the end of 2013, Watershed Management Group sent samples from each toilet to the University of Arizona’s microbiology lab for testing. Almost all the samples passed the EPA’s standards for what is safe to use in a garden, meaning that the temperatures reached during the composting process were enough to kill the harmful microorganisms. The two that didn’t pass hadn’t been given the four months needed to complete the composting process.

At the end of the pilot program, the Arizona Department of Environmental Quality (ADEQ) gave all the participants in the pilot program permits to continue legally using the toilets.

Catlow Shipek, policy and technical director and a founding member of Watershed Management Group, is currently working with ADEQ to approve the designs from the pilot program for widespread use in Arizona. When asked how long that process might take, he sighed, shook his head and said that it has already been much more challenging and time consuming than he expected.

“ADEQ is concerned about precedent, because if they do this, it sets precedent for someone else to submit their system,” Lowen explained. “So they want to ensure that they’re safeguarding public health and groundwater and not opening up the floodgates.”

David’s Barrel Design

David and Pearl Omick’s barrel composting toilet system in Cascabel, Arizona. The two barrels on the left are composting, and the barrel in the outhouse is in use. Because the outhouse faces the remote desert, there is no need for a door. (Photo by Michaela Webb / Arizona Sonora News)

David and Pearl lead the way down the wooden steps from their front door and along a dirt path weaving between creosote bushes and prickly pear cactuses. After about 50 feet, a small outhouse comes into view. Two 55-gallon plastic barrels sit next to the outhouse, sunk a few feet into the desert soil.

A third barrel, topped with a platform toilet seat and lid, sits inside of the outhouse. Imagine replacing the bowl of a traditional flush toilet with a blue 55-gallon barrel, and you have the idea.

David explains that they will use that barrel until it’s full, and then shift the outhouse and removable platform to one of the other two barrels. They leave the first to compost for about a year. When the transformation is complete, David and Pearl shovel the finished compost into a wheelbarrow and add it to their vegetable garden.

Although it’s not generally recommended to apply “humanure” compost to edible crops, David and Pearl said they have sent enough samples to a University of Arizona pathogen-testing lab over the years to be confident that the finished compost from their toilet is safe.

“Typically we’ll get salads throughout the winter from that garden. It produces like it’s on steroids,” David said, grinning. “The only thing we put into that aside from seeds is what comes out of the toilet.”

The Omicks’ composting toilet smelled better than most indoor bathrooms with flush toilets. This may be partly because air moves freely through the outhouse, but it’s also because the composting process, if done correctly, doesn’t produce much odor.

Microorganisms that thrive in hot conditions break down the waste. They also produce heat themselves, according to Watershed Management Group. These microorganisms need many of the same things as humans to survive: air, water and a food source (in this case, human waste).

David and Pearl use a compost crank—a long, metal corkscrew-like-device—to turn and aerate the compost in each barrel every couple of weeks to give the microbes air and expose them to new fecal material to process.  Turning the compost also ensures that all the waste in the barrel gets hot enough to kill bad microbes. They add a handful of wood shavings or another brown, carbon-rich source after they use the toilet. This ensures that the microbes have the right ratio of carbon to nitrogen (30:1 is ideal) to thrive.

A Visit With Dr. Germ

Dr. Charles Gerba knows what goes on inside a composting toilet. He studies germs. As an environmental microbiologist at the University of Arizona’s WEST (Water & Energy Sustainable Technology) Center, he conducted all the scientific testing for harmful bacteria in the composting toilets used in the Pima County pilot program.

High temperatures kill the harmful bacteria in composting toilets, Gerba said. The magic number is 131 degrees Fahrenheit.

After the composting process is finished, it’s important to let the compost sit for another few months to dry out. Even though the high temperature of the composting process should kill all harmful bacteria, letting it sit ensures that all pathogens die off because compost isn’t their natural habitat, Gerba explained. 

 “Most people want to flush it and forget about it,” he said.

The biggest barrier he sees to people installing composting toilets is enough dedication to go outside to use the bathroom, and a willingness to maintain the toilets.

Pilot Programs on Both Sides of the Border

The desire for composting toilets in Pima County is driven by environmental consciousness, said Dr. Diane Austin, professor and director of the School of Anthropology and a faculty member in the Bureau of Applied Research in Anthropology at the University of Arizona.

But composting toilet users have different motivations elsewhere. For example, in Nogales, Sonora, Austin helped start a composting toilet pilot program in 2007 and 2008—a few years before the Pima County pilot program began. 

While the Pima County pilot program aimed to reduce water use and improve soil quality, the Nogales pilot sought to improve public health and sanitation. Many neighborhoods in Nogales aren’t connected to sewers or running water. People in these areas either have septic systems or use open-pit toilets and latrines, which can contaminate water sources and food.

The Nogales pilot program used a double chamber composting toilet design, which works similarly to David’s barrel toilet, but is bigger and housed in a more permanent cinderblock structure. Instead of multiple plastic barrels, the double chamber system uses two large cinderblock chambers underneath a cinderblock outhouse. One side is used until it’s full, and then allowed to compost while the other chamber is being used.

In Nogales, many of the families who participated in the pilot program were living in houses constructed from pallets and wood scraps. Once the double chamber composting toilets were built, many families constructed new houses around the toilet because it was the most stable structure on the property, said Austin.

Having a composting toilet on the property could have the opposite effect for Tucsonans interested in installing composting toilets. Because composting toilets are such a fringe technology and public perception isn’t always positive, they could decrease property values, Austin said.

“Some of the people who came to the initial meetings (for the Pima County pilot program) and wanted toilets and then realized that ‘Oh, wait! Once I build this, it’s in my backyard and what if I want to sell this house?” Austin said.

In addition, if traditional plumbing and flush toilets break, homeowners can call a plumber. Even though composting toilets are much simpler, things can go wrong. Right now there aren’t composting toilet plumbers to call.

Composting Culture Change

David Omick doubts that composting toilets will become widespread. “Most people don’t want to deal with their shit,” he said. “Flush and forget. That’s the prevailing mindset. And until that changes, until we begin to see shit as a resource, if you will, until we begin thinking in terms of closing nutrient cycles, making better use of our water, beginning to see water really not just as a resource but a gift in the desert … until that happens, I don’t think composting toilets are going to be widespread.”

Chris Lowen, farm manager of Las Milpitas de Cottonwood community farm in Tucson, has seen firsthand the public’s perception of composting toilets. Las Milpitas participated in Watershed Management Group’s composting toilet pilot program, so they have a composting toilet on site. Most participants in the pilot program used David Omick’s barrel composting system, but built the larger double-chamber system used in the Nogales pilot program because of heavy demand by employees, 40 families with garden plots, and visitors attending educational events.

The composting toilet is the only bathroom at Las Milpitas. Once people see (and smell) the composting toilet, they don’t usually have any issue with it, Lowen said.

“It’s always the high school kids who you talk with about a composting toilet, and you can just watch their noses turn up. But then we go and look at it, and it doesn’t smell, and it’s nicer than some of the pit toilets that you get out in some of the parks,” he said. “It’s a culture shift.”

Even though test results show that the compost from the toilet would be safe to use directly in garden beds, Las Milpitas uses it only to fertilize landscape trees and fruit trees. Even though it would be safe, using the compost in garden beds might gross people out, Lowen explained.

Another barrier for people who want a composting toilet is that ADEQ still hasn’t approved the two designs tested in the pilot program for widespread use in Arizona. Even so, plenty of “rogue” users have illegal composting toilets in Southern Arizonaccording to Omick and Lowen.

If Watershed Management Group is successful in working with ADEQ to approve the two reference designs, Lowen said he hopes that composting toilets will become much more widespread in Arizona.

“I think the key is starting off with good examples, having some hard numbers and having people come out and smell it and being like, ‘All right, this isn’t bad!’” he said.

At the Omicks’ home in Cascabel, evening light slants through the western window, illuminating the twisting, knotted patterns in the wood floorboards. David, who is sitting on the bed because Pearl and I are using the only two chairs, leans back against the wall, head slightly tilted, mouth set.

“I tend to be a short-term pessimist and a long-term optimist,” he says. “I think that humanity, really in all parts of the world, is going to have some major adjusting to do, between climate change, resource depletion, widespread species extinction. Over the next century, there will be profound changes that are going to force people to reevaluate what our relationship is with the world we live in.” Of composting toilets, David says: “I really don’t see it becoming widespread until we’re forced into that.”


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