Composting In Schools

Estimating Carbon Content

Tom Richard

If you know the nitrogen content for an ingredient, but not the carbon content or the C/N ratio, you can estimate the % C based on the volatile solids content if that value is known or can be measured. Volatile Solids (VS) are the components (largely carbon, oxygen, and nitrogen) which burn off an already dry sample in a laboratory furnace at 500-600°C, leaving only the ash (largely calcium, magnesium, phosporus, potassium, and other mineral elements that do not oxidize). For most biological materials the carbon content is between 45 to 60 percent of the volatile solids fraction. Assuming 55 percent (Adams et al., 1951), the formula is:

% Carbon = (% VS) / 1.8
where % VS = 100 - % Ash


Adams, R. C., F. S. MacLean, J. K. Dixon, F. M. Bennett, G. I. Martin, and R. C. Lough. 1951. The utilization of organic wastes in N.Z.: Second interim report of the inter-departmental committee. New Zealand Engineering (November 15, 1951):396-424. Return to citation in text.


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