EFFECTS OF AERATION STRATEGIES ON THE COMPOSTING PROCESS: PART I. EXPERIMENTAL STUDIES

Abstract

The effects of aeration strategies (one-directional airflow, one-directional airflow with recirculation, reversed-direction airflow, and reversed-direction airflow with recirculation) on the composting process under intermittent aerationwith a 15 min on and a 45 min off cycle for all tests were experimentally investigated. Intermittent aeration was used in thesestudies because it has been shown to have higher efficacy (more energy efficient and less odor emission) than continuous aerationfor the one-directional airflow case. Paper mill sludge and broiler litter were composted using four 208 L stainless steelreactor vessels modified to allow studies on four different aeration strategies with a C:N ratio of 25:1. Compost mass wasdivided into five layers by polypropylene screens. Detailed analysis of the experimental data showed that aeration strategiesyielded different temperature, moisture, CO2, O2, and decomposition profiles. One-directional airflow yielded the highesttemperature, moisture, and decomposition gradient across the composting bed. The experimental data for one-directionalairflow with recirculation showed that the compost temperature profiles were smaller than for the no-recirculation case andwere similar to what was reported in the literature. Reversed-direction airflow had the smallest moisture gradient andmaximum moisture retention. Reversed-direction airflow with recirculation showed temperature and moisture profiles thatwere a superimposition of the results for the two independent aeration strategies. Oxygen levels, due to the on/off cycle patternand decomposition rates, limited performance and it was concluded that each system was not operated at the optimum point.Results of these studies will be used to validate finite-difference computer models, which can then be used to find the optimumoperating points for each system.