Check out Oregon Department of Environmental Quality’s hand out on Considerations for Installing a Composting Toilet System and recode’s National Model Code: Site-built and Urine Diverting Composting Toilets for IAPMO for information on design, construction, and maintenance.
About Composting Toilets:
Since their introduction in the 1960’s, designs for residential composting toilet systems have been extensively developed and studied in regions that lack soils or resources necessary for water-carried systems. Developed to provide sanitation with minimal resource inputs and in most designs no water, composting toilets can reduce water closet water usage by 100%, and overall lavatory water usage by 25% (calculation based on ICC 702).
A composting toilet system includes four parts: a commode, a collection method, a composting chamber, and a management plan. Most systems combine collection and composting, and some have commode, collection, and composting in a single unit. The broad morphological variety among composting toilet systems belies their functional similarity. In a composting toilet system the outcome is always the same– human wastes are decomposed into stable, soil-like humus, safe for application on trees and decorative plants.
The town of Falmouth, Massachusetts found that households with bathrooms retrofitted with composting toilets reduced the nitrogen output of the households by 82-96% (as measured by looking at nutrients in the graywater before and after the retrofits). The average cost of the retrofit per toilet was $5,435 in 2014. Nitrogen is a fertilizer for plants and often becomes a pollutant when it enters our water, causing algae blooms that suck all the oxygen out of water. Falmouth tried composting toilets to limit the amount of nutrients households were leaching into the shallow groundwater. In comparison the average septic system with leach field removes 10-40% of the nitrogen a household puts in (US EPA 2002 “Onsite Treatment Systems Manual” EPA/625/R-00/008).
Permitting Composting Toilets in Oregon:
Since 1978 composting toilets have been allowed as part of the Oregon state residential plumbing code (Oregon Revised Statues 918 770-0080) as long as they are evaluated to the NSF Standard 41 but the code also states that it is not “limited to” the NSF standard 41. Composting toilets can be approved for commercial installations by appealing to the local authority having jurisdiction.
Manufactured Composting Toilet Systems certified to the NSF Standard 41 include:
- Clivus Multrum
- Advanced Composting Toilet Systems (Phoenix)
Composting Toilet Installations in Oregon:
To date mostly manufactured composting toilet have gotten permits in Oregon, though at least one site built composting toilet design was permitted. The system was designed by Ron Davis and permitted in Lane County in 1980. In 1986 Davies said about 30 toilets of his design were installed in Oregon (Strycker 1986). It is unclear how many composting toilets of any kind are installed today.
Residential Installations: Desert Rain (installed Phoenix composting toilet in 2014).
Commercial installations: East Multnomah Soil and Water Conservation District (installed Phoenix composting toilet in 2009), Lewis and Clark College (installed Clivus in 2015). See Commercial Composting Toilet installations in Oregon by Recode for more information about these precedents.
Park Installations: Smith Rock State Park (installed Phoenix in early 2000s and Toilet Tech system in 2015) , Government Island State Recreation Area in the Columbia River (installed Phoenix in 2006 and 2011).
Build Your Own Composting Toilet:
The final draft of the Urine Diversion and Composting Toilet standards submitted by Recode volunteers, Mathew Lippincott, Molly Winter, Josh Klyber and Melora Golden, includes testing standards to encourage the installation of site-built composting toilet systems, which are often higher performance and lower cost than manufactured models (Davison 2003). These were adopted by an international codes organization (IAPMO) in 2018, so use them with confidence.