Composting Toilets

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Composting human feces solves multiple problems, while challenging cultural taboos around handling human feces.



The following notes are a summary of information provided by Tony Davidson, on and is reproduced here as a "fair use".

  • Joseph Jenkins (Humanure handbook) and David Omick provide public domain composting toilet designs.
  • Department of Ecology’s WAC 173-308 Biosolids Management is relevant for what to do with your poo when it is ready for distribution (the federal rule that the state law is modeled after is 40 CFR 503).
  • If greywater is produced at your location for showers, laundry, sinks etc. “an approved on-site greywater treatment and dispersal system, or public sewage system” is still required (RS&G 3.2).
  • There are various types of user built composting toilets, but one distinction to consider is whether the composting will take place where it touches the ground, or if it will take place inside of a container that does not leak water. Section 3.6.1 of the RS&G says that “For composting toilets installed entirely within a structure or a service vault, there are no specific set-back requirements” (i.e. distance to wells, creeks etc.). Here are those distances: (WAC 246-272A-0210 table IV) 200 feet from a public drinking water spring; 100 feet from a public drinking water well; 50 feet from a well, suction line, or surface water measured from the ordinary high-water mark; 10 feet from a pressurized water supply line; 5 feet from a property or easement line. If one or more of these water sources are too close to where you want to compost, I recommend checking out David Omick’s website “Barrel Composting Toilet System”
  • Before you distribute your compost, you will need to decide if you will manage it as domestic septage (WAC 173-308-270), which it is automatically considered, or biosolids (WAC 173-308 -210 or -250), which requires more testing and can be used on lawns or home gardens if it is Class A with respect to pathogens. Septage from composting toilets are exempt from the reporting requirements in WAC 173-308-295 and the permitting requirements in WAC 173-308-310 (WAC 173-308-193). Domestic septage must be incorporated into the soil (WAC 173-308-270 (3)(ii)). I will be placing my compost on native perennials which will die and turn to weeds if I disturb the soil, so I plan to manage my compost as biosolids, not septage. Which includes: not exceeding pollutant limits by not putting heavy metals into my compost (WAC 173-308-160); removing or not putting in plastic, glass or metal (WAC 173-308-205); significantly reducing pathogens by maintaining a thermophilic (> 113°F) compost pile—hold above 131°F for at least 15 days after the last poo of the batch is added (at least two bins or barrels are used to enable batch composting) (WAC 173-308-170 (3)(i)(B)); vector attraction reduction will be accomplished at the same time—113°F for 14 days (WAC 173-308-180 (3). Biosolids, and Septage, must be tested for at least nitrogen and applied to not over fertilize. Biosolids, not Septage, must be tested for pathogens (< 2 million fecal coliforms per gram is class B, < 1000 fecal coliforms per gram is class A) (WAC 173-308-170). Class A biosolids can be placed on lawns or home gardens (WAC 173-308-250). I plan to test my compost for nutrients and E. coli at Soiltest Farm Consultants, Inc. in Moses Lake for about $170. To find other approved labs, search for Washington State ecology lab search (search by matrix, solid and chemical materials).
  • Ensure that the compost maintains a moisture content of about 60 percent. Moisture content below 40 percent will slow decomposition and will increase the likelihood of fire ignition—you can be held liable for fire suppression costs (RCW 52-12-108 ). Moisture content above 75 percent will lead to anaerobic conditions (or not having adequate oxygen) which will slow decomposition and cause objectionable odor (hydrogen sulfide and ammonia) which must not migrate beyond property boundaries (WAC 173-350-220 (1)(c)(iii) and potent greenhouse gasses (methane and nitrous oxide).
  • Septic rule review is required every four years, and 2017 is the next review year, so now is the time for people interested in changing septic law to look at what specifically they want to change and speak up (WAC 246-272A-0425).