The role of periodic agitation and water addition in managing moisture limitations during high-solids aerobic decomposition

The results of this study were obtained from a pilot-scale experimental sys tem designed to mimic an agitated bed composting process. This choice of sc ale represents a compromise between a better controlled and reproducible be nch-scale system-and a reality-based full-scale system. Two substrates were studied: a synthetic food waste (dry dog food) and anaerobically digested, polymer-dewatered biosolids. The goal was to evaluate the degree to which periodic agitation: (1) lessened spatial gradients in moisture and temperat ure; and (2) thereby improved sustained degradation rates and cumulative ex tent of biodegradation. Coefficient of variation for cumulative O-2 measure ments in the three replications of the 55% dog food and wood chips experime nt with an aeration rate of 100 1 min(-1) were of the order of 25-30% which was consistent with other bench and pilot-scale studies. Drying occurred i n both static-bed and agitated-bed studies. However, moisture gradients in the agitated-bed were smaller than in the static-bed experiments. Also, dry ing of the solids matrix increased with increased aeration rates for all th e experiments. For the 45% dog food and wood chips experiments, a moisture content of 30% was reached in 180-300 h for aeration rates of 50-100 1 min( -1), respectively; while for the 55% dog food and wood chips experiments, 3 0% was reached in 320-480 h for aeration rates of 50-100 1 min(-1). The res ults of the water addition study showed that adding water three times per w eek resulted in a cumulative O-2 uptake at 622 g O-2 kg(-1) of TS at 496 h, a 48% increase over no water addition for an additional 96 h of decomposit ion, and a 26% increase over adding water once a week. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.