Effect of air recirculation and reuse on composting of organic solid waste

Composting has become increasingly popular in the past decade as a biological treatment process of organic solid wastes, generated from different sources, with the purpose of recovery, stabilization and volume reduction of waste material in the form of compost. In this study, the effect of different modes of aeration on composting of solid waste using two heat insulated closed pilot-scale reactors was investigated. The modes of aeration studied were upflow, downflow, alternate upflow/downflow, and internal recirculation in a single-reactor system as well as reuse of spent air in a two-reactor system in series. Composting tests were performed in two stages of 20-30 days duration each. Temperature at different heights of the composting mass as well as air velocity were continuously monitored by a datalogger. Air flow was continuous or intermittent depending on temperature. Oxygen content in the spent air was regularly measured. The results show that (i) the application of unidirectional upflow or downflow aeration creates significant vertical distribution of temperature in the composting mass; and (ii) internal recirculation of air in a single-reactor system and reuse of spent air in a two-reactor system appeared to achieve a more uniform temperature distribution and thereby accelerated degradation of the organic matter. Practical applications in composting plants are discussed. (C) 2001 Elsevier Science BN. All rights reserved.