Predicting Variations of Indexes for the Success of Composting Processes under Simultaneous Changes in Arbitrary Two Factors

Abstract

It is important for process design to predict properly the effect of variation of main factors concerning composting processes on indexes for their success. These factors are initial microbial concentration X_i, initial substrate concentration S_i, initial moisture content w_i, and aeration rate u. Final moisture content w_f, maximum attainable temperature T_max, amount of substrate consumption ΔS, and time required for finishing the process t_f were chosen as indexes for the success of composting. These indexes represent characteristics of composting products and conditions for proper composting. Through numerical experiments, it was discussed whether variations of the indexes could be approximated by a linear combination of contributions of changes in the individual factors, on condition that arbitrary two factors would change simultaneously. Contributions of the changes in the individual factors to the indexes were estimated in advance, assuming that the value of each factor varies solely from its default value. Among four indexes, T_max seemed to be hardly influenced by the variation of factors, however, deviations of w_f, ΔS, and t_f could not be predicted well by the linear combination of the contributions of changes in individual factors, especially when S_i and w_i would change simultaneously.