The Fate of Elements in Residential Composters

An investigation into the fate of elements during residential composting was conducted by studying an Envirocycle residential-type aerobic composter unit that was set up and operated at the University of Toronto's greenhouse facility. Source materials consisting of various fruits and vegetables were combined with Metropolitan Toronto Works Department's finished leaf compost (MWFLC), and composted over a 2-month period. Instrumental neutron activation analysis (INAA) was used to determine the concentrations of Al, As, Ba, Ca, Co, Cr, Fe, K, Mg, Mn, Na, Sb, Sr, Ti, V, and Zn in the source materials and the 2-month greenhouse finished compost (GHFC). Results indicate that the ratio of final element mass to input element mass was approximately 1, suggesting that elements are conserved during the composting process. One tailed t tests (0.05 level of significance) on element concentrations between the MWFLC and GHFC revealed that supplementing MWFLC with fruits and vegetables does not significantly change concentrations >25%. One-way analyses of variances conducted on Toronto residential compost samples revealed good homogeneity within an individual composter, although significant elemental variances occurred between separate composters. Incidentally, it was noticed that several of the Toronto residential compost samples had Cr levels that exceeded Ontario Ministry of Environment and Energy guideline values for municipal compost.