Barrel Composting Toilet System:
Pathogen Testing Methods and Results

(Updated 11/01/2013)

Periodic testing for E. coli in samples of aging compost from the Barrel Composting Toilet System was performed from mid-February through late April of 2012.  The toilet was in an outdoor location.  Samples of compost were collected from a barrel that aged from January through April.  Average ambient air temperature during the test period was 53 degrees Fahrenheit (according to NOAA Normals Data Access).  Microbial testing for the indicator bacteria E. coli showed no colonies in samples after 4 months of aging.  

Samples of compost were collected and processed according to National Sanitation Foundation (NSF) guidelines, Standard 41, Sections 12.1 - 12. 3.  For each test, 5 samples were collected.  Samples weighed 10 grams each.  Samples collection points were evenly distributed from throughout the barrel and were representative of the contents of the entire barrel.  The 5 samples were thoroughly mixed together prior to testing. 

Testing was performed once per month for 4 months using Coliscan Easygel test kits at the manufacturer's recommended dilution of 100x.  Samples were incubated at 40-44 degrees Centigrade for 48 hours, per manufacturer's recommendation.

Testing at monthly intervals during the first 3 months of aging indicated E. coli colonies in excess of the NSF maximum of 200 colony forming units (CFU) per gram. 

Samples tested at 4 months of aging showed 0 CFU following 48 hours of incubation.  

Corroborating with these results, more recent testing was performed by the University of Arizona on finished compost samples from 5 different Barrel Composting Toilets Systems in the Watershed Management Group's composting toilet pilot project.  All 5 samples qualified as Class A Biosolids in terms of pathogen levels.  According to the Environmental Protection Agency (see item #18 in this link), "In general, exceptional quality (Class A) biosolids used in small quantities by general public have no buffer requirements, crop type, crop harvesting or site access restrictions."  

Note that, as a safety measure due to the many variables in composting toilet use and to the experience necessary to insure complete composting, we do not recommend the use of finished compost on edible crops by the general public.

Testing by the University of Arizona is ongoing and test results will be posted here as they become available.  


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