Large quantities of solid wastes are generated daily in municipalities, industries, and agriculture. In the past, landfilling was an economical disposal method. However, as space has become less available, other options are being considered. Composting is a method of diverting organic material from landfills and recycling a valuable resource as a soil amendment.; Although the biodegradability of influent water is routinely measured in the design of wastewater treatment facilities, construction of compost systems is often based on biodegradability values from the literature. However, lack of defined and standardized conditions limits the usefulness of these data. In addition, many of these literature values were determined during anaerobic studies, and their applicability to aerobic composting systems is questionable.; In this study, the biodegradabilities of four solid wastes and two bulking agents were measured in bench-scale, aerobic reactors. The biodegradabilities of the solid wastes and the length of time required for the completion of the high-rate phase of composting were different for each waste. The contribution of sawdust to total carbon dioxide production in the compost mixes was significant.; Because composting is dependent on microbial activities, levels of microorganisms were monitored by plate counts, staining with 4,6-diamidino-2-phenylindole (DAPI), and quantification of ATP levels. Overall levels of microorganisms did not increase sufficiently to account for total amounts of carbon dioxide produced during composting. Within the microbial community, there were shifts in subpopulations as detected by use of a spot-plate technique. In pulp and paper-mill primary solids, the BIOLOG system was used to follow changes in the composition of identifiable microbial populations.; Microbial exoenzyme production on selected macromolecules was monitored on spot-plates. Levels of exoenzymes produced were generally lower on {dollar}alpha{dollar}-cellulose than on cell-wall, casein, or starch agar media.; Municipal solid waste and pulp and paper-mill primary solids composts were examined for the presence of anaerobic microorganisms. Anaerobes were isolated throughout composting. If microbial levels on spot-plates correspond to metabolic activity in the composts, anaerobic microorganisms may be responsible for a significant portion of the metabolic activity in microenvironments of aerobic composts.
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