Pressure drop through raw food waste compost containing synthetic bulking agents

The pressure drop of air forced through a column of raw vegetable waste com post was measured for six different synthetic bulking agents and compared t o pine bark as a reference. The volume of each bulking agent used per mass of compost material, referred to as the bulking agent ratio, was used to co mpare these bulking agents. Results indicate that synthetic bulking agents reduce the pressure drop significantly more than pine bark for any given bu lking agent ratio and air how. The pressure drop measurements were regresse d to three pressure drop-flow models, and these models were similarly succe ssful in predicting the observed pressure drop behaviour. To quantify the i mpact of bulking agent ratio on pressure drop, a two-parameter empirical re lationship was proposed between the bulking agent ratio and the linear coef ficient of Ergun's model (model 3) or the coefficient in Shedd's model (mod el 1) forced to an exponent of 1.0 or 1 1. One of the parameters in this pr oposed model is the bulking agent ratio necessary to reduce by 50% the visc ous energy losses of air flow through the compost column. Using the empiric al model to compare this parameter among bulking agents used, the synthetic bulking agents were demonstrated to be approximately 3-10 times more effec tive than pine bark. The utility of this model to aid the optimization of t he bulking agent ratio is also discussed. (C) 1999 Silsoe Research Institut e.