The Moldering Privy

Green Mountain Club Exit Strategies - 2010

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Double Crib Privy at Spruce Ledge Camp

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History in Vermont

•  Concept introduced to Long Trail/Appalachian Trail System in 1997 by Green Mountain Club Volunteer Dick Andrews. 1st site was Little Rock Pond Shelter in 1997.

•  Concept based on Andrew’s Clivus Multrum composting toilet in his home – same composting techniques used.

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Moldering Defined

•  Moldering method of composting employs mesophilic temperature range (68° to 112°F). AKA “Slow Composting.”

•  Not hot enough to kill disease-causing pathogens.

•  Moldering toilets substitute long retention time of waste to ensure pathogen destruction – minimum of 2 years. The longer the better.

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Moldering – Where to use? •  At low to medium use sites. •  Defined as a site where it will take a minimum of 2+

years for one crib to fill up. If it fills faster than this a batch-bin or commercial system is called for. Alternately you can build more cribs – you as a manager need to determine how many cribs you can accept environmentally and aesthetically. GMC limit is two cribs.

•  GMC recommends you choose a site where you believe you have low use and where you can measure the use. See how long it takes to fill a crib – use this data to define your “use threshold.”

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Original Crib design circa 1999 – Single Crib, 6x6 construction

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Drilling Pilot Holes for rebar

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Cribs are held together with rebar that link together each corner and are embedded in the ground.

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Note 2x4 corner bracing

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Raising Outhouse onto Crib System

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Existing Outhouse is placed on crib system

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Finished Single Crib unit. Privy attached to crib with angle brackets

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The finished unit is tall. Stairs or an Accessible ramp/stair system is required.

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Design Principles

•  Basic Crib Capacity is 4’x4’x3’ (w/l/d). •  Shallow depression is made in the ground

below the crib to focus blackwater into biologically active soil.

•  Air Slots are covered on both sides with hardware cloth and externally with dark insect screening to prevent waste escape and vector access.

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Design Styles •  Original design utilized 6x6 timbers (treated and

untreated). •  Easy to design and build but very heavy to pack to

remote backcountry campsites. A second or third crib would need to be packed in when the first one was full.

•  Current design is a two-chambered unit built with 4x4 uprights held together with 1x6 horizontal members. The composting crib is covered with a removable roof system. This unit is much lighter, easier to pre-build in the frontcountry, and is more readily adaptable to double and triple-chambered units.

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The new design is a double-chambered unit. The basic frame is composed of six 4x4’s each 3 feet tall.

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Puffer Shelter System under construction – new privy and cribs.

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Note strapping used to reinforce hardware cloth to crib.

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Installing hardware cloth. Note divider separating two cribs.

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Corner Bracing provides extra strength.

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Securing 1x6 horizontal members

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Finished crib system contains 21 main structural pieces.

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Top sills are attached with metal plates.

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Attaching stair treads.

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Finished 2 chambered system showing installed hardware cloth, insect screening, and composting bin cover.

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Finished 2-Chambered Moldering Toilet

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Modified Moldering System w/ Liquid Separator

•  Installed at AMC’s Upper Goose Pond Cabin.

•  A caretaker periodically homogenizes the waste and adds bulking agent as needed.

•  Crib is shallower and thus requires regular tending to prevent overflow.

•  Liquid separator requires a separate seat and drains to a modified French Drain.

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Upper Goose Pond Moldering Toilet – Note shallow cribs.

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Access Door and urinal drain hose

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Access Hatch – provides access for knocking down the cone.

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Accelerated Moldering Process – Bulking agent is leaves and forest duff.

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Removing finished compost for spreading on the forest floor

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Side by Side: Urinal on left and solid waste hole on right.

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Unisex Urinal

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French Drain for Urine

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Clivus-Style Moldering Privy

•  Constructed on the Appalachian Trail in Maryland and Pennsylvania.

•  Utilizes large sloping chamber. •  Dual Chambered Units create long retention time

for waste. •  No contact with soil – needs large base of

bulking agent added to create composting “bed.” •  System improvement needed: liquid drainage

system to French Drain or Beyond the Bin Barrel.

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Single Chamber Clivus Style “Pennsylvania Composter.”

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Double Chambered Unit under construction.

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Current Design – Lessons Learned

•  Bulking agent (carbon source) must be brought in. Reliance on area leaves and duff proved hard on the resource. GMC has had the most success with dry softwood planer shavings – most absorbent.

•  A base of 4 to 6 inches of bulking agent should be added to bottom of the crib to create a composting bed. This assists in aeration and increases percolation of liquids by providing separation.

•  An access lid must be incorporated into the design so the cone can be knocked over periodically and the waste pile homogenized. Access through the seat is unsanitary.

•  Pile can and will dry out if the manager does not monitor pile moisture and add water as needed. A dry pile will not compost – pathogens go dormant and persist.

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Current Design – Lessons Learned Continued

•  GMC has begun to perforate the roof cover that goes over the composting crib so that rain water can percolate in and keep pile moist. For the active pile we ask users to urinate on the pile – unless use levels create an objectionable odors.

•  GMC has added a sloping metal roof cover to the composting chamber to prevent excessive moisture and reduce the chance of cave-in from heavy snow load.

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Resources

Appalachian Trail Conservancy and Green Mountain Club’s Backcountry Sanitation

Manual (1st edition 2001)

http://atfiles.org/files/pdf/atcsanitation.pdf

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Thank You

WWW.GREENMOUTAINCLUB.ORG