Plant-derived cellulosic materials play a critical role when organic wastes are composted to produce a beneficial amendment for topsoil. This review article considers publications dealing with the science of composting, emphasizing ways in which the cellulosic and lignin components of the composted material influence both the process and the product. Cellulose has been described as a main source of energy to drive the biological transformations and the consequent temperature rise and chemical changes that are associated with composting. Lignin can be viewed as a main starting material for the formation of humus, the recalcitrant organic matter that provides the water-holding, ion exchange, and bulking capabilities that can contribute greatly to soil health and productivity. Lignocellulosic materials also contribute to air permeability, bulking, and water retention during the composting process. Critical variables for successful composting include the ratio of carbon to nitrogen, the nature of the cellulosic component, particle size, bed size and format, moisture, pH, aeration, temperature, and time. Composting can help to address solid waste problems and provides a sustainable way to enhance soil fertility.

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The aim of this research was to study the anaerobic conversion efficiency of the organic fraction of municipal solid waste (OFMSW). In order to compare and appraise our techniques and respective conversion efficiencies, primary sewage sludge (PSS) assays were also performed. OFMSW has a high cellulose content (32.9% TS) followed by lignin (12.5% TS), protein (9.61% TS), lipids (5.94% TS) and hemicellulose (5.2% TS). PSS is equally rich in lipids (19.8% TS), protein (18.2% TS) and lignin (19.6% TS), followed by cellulose (13.4% TS) and hemicellulose (5.5% TS). Assays were run in CSTRbiodigesters operated at 35°C and 20 days hydraulic retention time (HRT). Three organic loading rates - 1.0, 2.7 and 3.8 OFMSW g VS/Lr.d (gram of volatile solids per liter of reactor per day) - were studied. PSS was assayed only at 1.0 g VS/Lr.d. Concerning the conversion efficiencies, the most important component for the OFMSW anaerobic digestion is cellulose (74.0 - 77.8% conversion), while lipids (70.0 - 80.6% conversion) are the most important for PSS. The biodegradability of the other organic components are also presented and discussed. Some literature data about OFMSW anaerobic digestion processes are discussed in view of the results presented here. The similarities between our results and those of the so-called dry fermentation processes are also discussed in order to evaluate efficiencies of biogas and CH4 production versus volatile solids removal.

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