The Effect of Moisture On Air Classification of Municipal Solid Waste

Abstract

The effect of moisture on the air classification of municipal solid waste (MSW) is analysed using a 23 factorial design. A synthetic MSW is used in the laboratory to facilitate controlled variation of composition and moisture content. A pilot scale 120° zig-zag air classifier is used to perform the classification tests. Ten system response variables are evaluated including six recoveries, two purities and two efficiencies, to elucidate the impacts of (1) increased particle density resulting from moisture absorption and (2) particle adhesion. Results indicate a significant decrease in paper recovery and efficiency with increasing moisture. However, no significant reduction in aluminum and iron recovery is observed. This suggests that adhesion of these particles to extracted combustible materials is not a significant factor in reducing extract purity. Instead, extract purity reduction is a result of paper recovery losses from increasing particle density. The degree of moisture effect for varied MSW composition is greater for feeds with lower fractions of adsorbent materials. A redefination of percent moisture based on the MSW absorbent fraction is suggested in order to account for this varied impact. The new definition, moisture absorbancy ratio, is the weight of the moisture in the MSW divided by the dry weight of the absorbent materials in the MSW.