|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
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.