Notes From the Field Station: Composting Toilets

19 Oct

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In my previous post I outlined the current design for the Bechtel Environmental Classroom at the MacLeish Field Station. Due to the brevity of the post, I touched upon many interesting and complex aspects of the design but failed to fully explain their significance in the context of satisfying the imperatives of the project (as outlined by the Living Building Challenge). In my next couple posts I plan on elaborating upon some of these innovative systems, more specifically clarifing how they function and their specific role in the design. Today I will be focusing on a highly essential portion of the design, the choice to incorporate composting toilets instead of traditional flush or dual flush toilets.

Throughout the history of human civilization we have designed and utilized a variety of human waste disposal systems, ranging from the latrine and privy in early civilizations, to the flush toilet, dual-flush toilet, and composting toilet of the modern age. Due to imperative value of water as a limited natural resource, many contemporary environmental designers and planners consider composting toilets the gold standard for human waste disposal systems. However, although composting of food scraps and plant material has gained enormous acceptance throughout much of the developed world, many people remain hesitant to make the jump to composting human wastes as well.

In brief, composting toilets are structures that utilize microbes to decompose human wastes for use as a nutrient-rich soil additive for ornamental or edible landscapes, acting to transform a traditionally thought of “waste” into a “resource”. They range considerably in aesthetic, from the sleek white models that mimic traditional toilets, to rustic, handmade varieties. Nevertheless, they all attempt to copy the environment of a forest floor, which decomposes animal wastes to produce valuable nutrients for the surrounding vegetation, or humus. Additionally, these systems require little to no water, drastically reducing the overall water and financial burden of a building.

 The average American uses 74 gallons of water a day, a third of which goes directly into operating toilets, about 25 gallons.

Maintenance of composting toilets are quite minimal, requiring only periodic additions of coarse carbon-based bulking materials (i.e. sawdust, dry leaves) in addition to removal of the seasoned humus at the base of the composting chambers every 6-12 months depending on intensity of use.

One person using a composting toilet would produce about 80 pounds of humus and save more than 6,600 gallons of water per year. 

Joseph Jenkins, author of The Humanure Handbook, calls the fear that humanure is unsafe for agricultural or ornamental use “fecophobia”. He acknowledges the potential for humanure to carry pathogens, but explains that this potential is directly linked to the state of health of the individuals that are producing the excrement. Scientific analysis of samples taken from composting toilets have found that adequate time (minimum of a few months) and temperatures generally will make human manure safe to use, even though many local laws refuse to acknowledge this fact. For example, many states still require the end product of a composting toilet system to be removed form the site by a sewage hauler or buried under 6 inches of soil.

This all being said, it is very exciting that the Bechtel Environmental Classroom design team has chosen to include composting toilets in this project. I look forward to seeing this highly sustainable system in action, and hope that by exposing students and faculty to this alternative, it will begin to become more accepted and encouraged at a larger scale.

-Jessa Finch (’12)

CEEDS MacLeish Intern

2 Responses to “Notes From the Field Station: Composting Toilets”

  1. Amber Johnson October 20, 2011 at 11:41 pm #

    Will CEEDS be able to use the humanure collected in its composting toilets?

    • Smith College CEEDS October 21, 2011 at 5:33 pm #

      Hi Amber,

      You asked a great question. I will have to follow up with Reid Bertone-Johnson, who manages MacLeish, but the short answer is that the compost will eventually be used somewhere- it just may or may not be on one of Smith’s properties. I’ll try to find out more for you and fill you in soon. Thanks for reading!

      Sarah and the CEEDS team

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