Sequential Batch Anaerobic Composting of the Organic Fraction of Municipal Solid Waste

Abstract

When kept free of toxic components, the biodegradable fraction of municipal solid waste (MSW) may be decomposed by aerobic or anaerobic composting and the residues either disposed of by land application or marketed as compost. Anaerobic composting is more economic because it effects similar conversion, does not require mixing or aeration, and produces the valuable energy product methane. This paper describes technical performance and systems analysis of a novel sequential batch anaerobic composting (SEBAC) process for treatment of high solids wastes that employs leachate management to provide organisms, moisture, and nutrients required for rapid conversion of MSW and removal of inhibitory fermentation products during start-up. The results of 19 trials with this system operated at 55°C and total residence times of 21 or 42 days exhibited about 50% conversion of organic matter with a methane yield of 0.2 m3 kg−1 volatile solids. The process was reliable and stable. A systems analysis showed that tipping fees employing this process were in the $30 per ton range and that economics were highly sensitive to biodegradability of feedstock and residue use options; they were relatively insensitive to process kinetics and leachate recycle rate. This process can be applied to in-vessel or controlled landfill designs.