Southwest Environment

Stories written by University of Arizona students

Department of Soil, Water and Environmental Science
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The composting process requires balance, heat

By Lisa VanWagenen

By following a simple recipe, and by adding the proper ingredients, people can find that using composting toilets is a piece of cake – sit down, relax, and let the microbes take care of the rest.

Maintaining correct levels of nitrogen and carbon is important. Too little nitrogen with too much carbon causes the composting process to slow. The reverse amounts cause the compost to smell, explained Joe Silins, project manager with the Tucson-based Watershed Management Group.  

“That’s the thing about composting,” he said “You always want that carbon to nitrogen mix.”

The main source of nitrogen in composting toilets is the fecal matter, while the carbon is upheld with added green or brown waste. These can be materials like mesquite leaves (green) or sawdust (brown).

After every use, the material should be covered with the green or brown waste. This can help reduce foul odors and unpleasant sights. Periodically, the toilet’s contents should be stirred. Stirring adds oxygen to the pile, which allows the compost to break down faster.

A closer look into the compost pile, even closer than what one can see with the naked eye, reveals there is a population dominated by microorganisms. 

Microorganisms such as bacteria and fungi might not sound beneficial, but in a compost pile, they are essential in the breaking down of organic material. 

Microorganisms inside the compost pile generate the heat, which is critical in the process of composting, explained Charles Gerba, professor of environmental microbiology in the University of Arizona’s Department of Soil, Water and Environmental Science,

“If you keep the heat in there, it can kill out all the pathogens,” he said.

With millions of organisms per gram of compost, the internal heat of a compost bin can reach 122 to 131 degrees Fahrenheit, Gerba said. Microorganisms break the compost down into organic elements, while the heat that is generated kills pathogens.

If finished compost is to be used as a fertilizer, it is important that all of the pathogens are eliminated, Gerba said.

“One of the ways diseases are transmitted is by poop,” he noted.


End of Fall 2012 storeis
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