Moldering Privies 101 [Video]

December 12, 2016

The phrase, “it’s a dirty job, but somebody has to do it” perfectly sums up one key responsibility for AMC’s Backcountry Caretakers. Where there are humans, there is waste, and each year our fleet of campsites composts roughly 2,500 gallons of it. To help us manage human waste at this incredible scale we utilize a variety of available technologies, including the Moldering Privy. We hope this video gives you an appreciation for the work AMC’s Backcountry Caretakers perform not only to protect our environment, but to improve your experience when nature calls.

Interested in learning more about Moldering Privies? We’ve compiled a guide just for you!

What is a ‘moldering privy’ design?

The ‘moldering privy’ design is based on a principle of continuous and cold composting. The basic design consists of a conventional outhouse on a cribbed foundation, ‘crib’ meaning an above-ground box foundation with air flow. Waste collects in the crib, and rests above ground. Decomposition and treatment of the waste occurs through the slow collection of waste.

How does it work?

The moldering privy operates through continuous decomposition. Continuous decomposition occurs in colder temperatures (between 40F and 100F).

Moldering outhouses are suitable for low-use situations when the waste is added too slowly to provide enough fresh waste to reach a high temperature. High temperatures (above 99F) occur only when a large amount of fresh waste is added and the pile is stirred, turned, and manipulated regularly.

The moldering outhouse design can be modified to meet almost any situation and level of use. Multiple cribs, such as two or three crib-chambers, have been used successfully in medium-use sites in New Hampshire, Maine, Vermont, and Connecticut.

Moldering Privy

Why is it the most effective waste water treatment of all backcountry outhouses?

The moldering privy technology treats waste water in two ways:

  1. The majority of the liquid that enters the pile is dried out before it reaches the ground, through aerobic composting activity.
  2. The liquid that does enter the ground enters the organic surface soil, and is absorbed and does not travel beyond the footprint of the outhouse.

The crib that collects waste sits above a shallow depression, only a few inches deep, that focuses liquids so they will percolate into the biologically active layer of the soil directly beneath the pile.

The moldering privy reduces the likelihood of wastewater pollution and groundwater contamination. Many backcountry privies are in areas with seasonal high water tables, and consequently will have their pits filled with water for a third of the year, or more. This results in anaerobic conditions, which further the propagation of pathogens, and groundwater contamination.

The moldering privy sits on top of the surface of the soil and eliminates the need for a pit altogether. The composting mass cannot become waterlogged, so any liquid that drains through the pile is exposed to aerobic treatment before entering the soil. The majority of wastewater is dried out before it reaches the ground, and the organic soil is adequate to absorb the relatively low volumes of liquid deposited in a waterless toilet.

Moldering Privy

What are the benefits?

  • Sustainability: Due to the low annual maintenance cost and resources required, the moldering privy is the most sustainable composting outhouse design.
  • Low-cost: The initial construction costs are minimal given the size of the outhouse.
  • Minimal commitment for annual maintenance: Once moldering privies are installed, most maintenance can be accomplished by one volunteer visitng the site three to four times a year, although more frequent attention may be needed at high-use sites. (‘High-use’ meaning over 500 a year).
  • Low odor: The moldering privy reduces offensive odors through allowing air to flow freely around the compost, otherwise known as aerobic composting. Anaerobic outhosues (such as pit toilets or chambers) produce strong odors that often lead to hikers refusing to use these toilets because of the odor.

What land managers and agencies have approved this technology on their lands?

New Hampshire: White Mountain National Forest; Appalachian Mountain Club

Maine: Maine Bureau of Parks and Lands; Town of Newry, Maine

Vermont: Green Mountain National Forest

Connecticut: State of Connecticut

Moldering Privy

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Joe Roman

AMC Outdoors, the magazine of the Appalachian Mountain Club, inspires readers to get outside and get engaged. Learn more.