Southwest Environment

Stories written by University of Arizona students

Department of Soil, Water and Environmental Science
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Tucsonans test flush-free composting toilets

By Lisa VanWagenen

At the Watershed Management Group facility, David Omick (left) instructs program participants on how to install and use their composting toilets.
Photo courtesy of the Watershed Management Group. Used with permission.
At the Watershed Management Group facility, David Omick (left) instructs program participants on how to install and use their composting toilets.
While most Tucson residents with composting toilets are operating on the downlow, Joe Silins has a legal one of his own. Standing in the comfortable confines of the wooden structure, tin roof overhead, he describes it as hurricane ready.

“It’s burlier than your average composting toilet,” said Silins, referring to the structure that houses his composting toilet. Silins is one of 18 Tucsonans who has a legal permit to keep an alternative wastewater treatment system on site – in this case, a closed barrel that allows no drainage.

Silins is a project manager with the Tucson-based Watershed Management Group. This past summer, the WMG installed 18 composting toilet systems in southern Arizona, including the one at his home near Reid Park. The Arizona Department of Environmental Quality provided the temporary permits and an Environmental Education Grant from the Environmental Protection Agency provided the funding for the pilot project.

The toilets used for the project are called barrel-composting toilets. They look much like a normal flushing toilet, but they harbor impermeable 55-gallon barrels instead of a bowl. The wooden lid seals tightly enough to keep unpleasant odors from escaping. There are also two vents that aid in displacing odor by circulating air through the barrel.

Without needing to be flushed, composting toilets can conserve gallons of water with every use. It has other benefits, too.  

“It’s all about replenishing desert soils,” explained Silins, who noted that the composting project is a part of a WMG initiative called Soil Stewards, which aims to offer urban dwellers a chance to have healthy, useable soil – something that compost can encourage.

Composting is a sustainable way to dispose of food waste and other throwaway items, like garden clippings. More controversial and often misunderstood is the ability to compost human feces. If prepared correctly, Silins said, these wastes can be composted into a fertilizer that can be used on plants.

Charles Gerba eats lunch in his office while discussing composting toilets on a November afternoon.
Photo by Lisa VanWagenen.
Charles Gerba eats lunch in his office while discussing composting toilets on a November afternoon.
WMG has enlisted Charles Gerba, professor of environmental microbiology in the University of Arizona’s Department of Soil, Water and Environmental Science, to test the finished compost.

Sitting at his office desk eating his lunch on a November afternoon, Gerba explained his involvement in the WMG’s pilot project.

“We’re looking for indicators that all the fecal bacteria have been killed,” Gerba said.  

The results will go to the ADEQ for the purpose of collecting and studying data.

"The compost should be ready for testing in the next four to five months", Silins said.

"We’re still early in the phase," he said.

Achievement at the pilot sites could eventually ease some of the legal requirements to obtain a composting toilet. Currently, an Arizona Department of Environmental Quality general permit for a composting toilet costs $1,200 – many times the cost of a conventional toilet.

As for the toilets themselves, they must be obtained from a list of products that have been reviewed and approved by the ADEQ. The products range from a composting toilet that allows two uses a day for $2,279 and go upwards from there.

The system used by the WMG, designed by longtime composting toilet proponent David Omick, costs about $325. It’s up to the individuals to create their own structure around the toilet.

To monitor and evaluate the safety of the compost and the structure itself, inspectors like Pedro Robeles, a student worker for the Bureau of Applied Research in Anthropology, frequent the pilot sites. The inspectors also check in on the user-friendliness of composting toilets.

On an afternoon in October, Robeles led the way to a pilot site that he was inspecting. There was a blinding light gleaming in the front yard. When the shine disappeared, in its place sat the offender – a solar oven.

Robeles’ knock was answered by a kind smile from Shay Salomon, a participant in the pilot project. As Salomon led the way to the backyard, she warned her guests to be cautious of the pesky mosquitoes, and pulled out a bottle of natural bug repellant to share.

In the backyard, behind the tall screen of a crescent-shaped brick wall, sat the composting toilet. Salomon showed off her system, while Robeles assessed its condition.

When asked if she had found any outstanding problems, Salomon mentioned having trouble with balancing the moisture levels. As she lifted the lid to turn the toilet’s contents, she added a hand full of shredded scrap paper and recalled an incident of extreme moisture.

Her family had been on a summer vacation. At the peak of Tucson’s monsoon season, the neglected compost sat, battled the fierce rains, and awaited their return. When she went to tend to the toilet “it was like a pond!” she explained.

The rain had permeated between the toilet lid and its wooden frame, and also into the two vents. Salomon said this problem was easily reversed. 

Salomon is not alone in her battle with moisture. When asked about negative user feedback, Silins explained that the most common problem has been moisture content.

When the compost barrels have been too wet, he said, users have had issues. The constant exposure to dampness can cause the wooden seat to crack. In some cases participants have noticed an undesirable number of bugs in the bottom of their barrels.

Moisture levels can be a sensitive factor in compost fertility. Toilets producing useable compost should achieve a balance among five fundamental factors: nitrogen, carbon, oxygen, temperature and moisture. (See related story.)

Composting toilets can be a means of boosting sustainable practices, but they can also help users become better in tune with their relationship with nature, Silins said. The ability to use homemade fertilizer on a home garden to grow food that is eaten completes a nutrient cycle.

By the project’s end, Silins said, WMG employees hope to overcome social and community barriers around composting toilets while also addressing current permitting barriers in Arizona.

If WMG’s goals are met, composting toilets could become more and more common in Tucson, but that does not mean they will become the predominant toilet.

“There have been years of cultural training to getting rid of your fecal matter by flushing it away,” Gerba said. There may always be some aversion to composting toilets because, as Salomon put it, “This is not for the faint of heart.”

Lisa VanWagenen is a Soil, Water, and Environmental Science major at the University of Arizona. She is a compost technician with the U of A Compost Cats and enjoys operating the tractor during farm work at the U of A's West Agricultural Center. This story was submitted for publication on December 11, 2012.

Arizona Department of Water Quality information on composting toilets

UA Department of Soil, Water and Environmental Science

Watershed Management Group

see related story
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