Calculating the Reduction in Material Mass And Volume during Composting

Loss of mass and volume during composting of various feedstocks is an important consideration for compost operation management and facility design. Direct measurements of mass and volume in piles and windrows require specialized equipment and skills that render such measurements impractical for most commercial operations. A study was undertaken to develop a technique for calculating reductions in mass and volume during composting based on the change in concentration of an internal standard and bulk density measurements. Of the various physicochemical parameters investigated, nonvolatile solids (NVS) content proved the most reliable internal standard because of its strong inverse correlation with organic C (r² = ?0.95) and low coefficient of variation (CV = 0.15). Reductions in mass and volume during composting of six windrows comprised of various feedstocks were then calculated using initial and final measurements of NVS and bulk density. Reductions in mass averaged 19.4% of initial mass and ranged from 11.5% to 31.4%. Volume reductions were substantially greater than mass losses, and averaged 40.7% of initial volume. Change in mass was used in combination with organic C contents to calculate the loss of organic C. These losses averaged 28.9% and represented an average 46.4% of total mass loss. Equations for calculating reductions in mass, volume and organic C are presented. These equations may be easily modified to calculate the loss of any measured constituent of compost where the initial and final concentrations are known.