Assessment of the residue quality and exportable energy from, and digester behavior during, the anaerobic digestion of municipal solid waste.

摘要

This study represents an effort to better define the capabilities of anaerobic digestion as a method for disposal of municipal solid waste. The primary issues addressed herein are: (1) the long-term stability of an anaerobic digester using an MSW feed; (2) the characteristics of the solid digestion residue, or digestate; and (3) optimization of exportable energy (methane production) from the digestion process.; The experiment employed a two-level factorial design with three variables--hydraulic retention time (HRT), solids retention time (SRT), and leachate flow direction (upflow vs. downflow)--resulting in a total of eight treatments. The treatments were conducted on two identical three-stage sequenced batch digesters.; The digesters exhibited excellent stability over the duration of the experiment (420 days), although one digester failed near the end of the experiment. Failure probably resulted from a combination of: (1) operating conditions under which the digester could not sufficiently resist destabilizing influences, and (2) such a destabilizing influence.; Metals, especially heavy metals, tend to concentrate in digestates vis-a-vis their feeds. Based on existing regulations for land application of compost, the digestates produced during this experiment nonetheless would be allowable soil amendments.; Use of the shorter experimental HRT (10 days) versus the longer HRT (30 days) resulted in significant increases in both daily methane generation rate and specific methane production. Average per-treatment methane generation rates under the shorter HRT ranged from 0.22-0.42 volumes per digester volume per day (vvd), while under the longer HRT they ranged from 0.08-0.18 vvd. Average per-treatment specific methane productions under the shorter HRT ranged from 95.6-118.0 L/kg dry volatile solids (VS) loaded; under the longer HRT, they ranged from 21.1-64.2 L/kg dry VS.; Use of the shorter HRT also resulted in significantly greater feed mass losses than use of the longer HRT. Use of the longer SRT (63 days) resulted in significantly greater feed mass losses than use of the shorter SRT (42 days).