Effect of initial material bulk density and easily-degraded organic matter content on temperature changes during composting of cucumber stalk

Abstract

To inactivate the potentially pathogenic microorganisms and safely utilize vegetable waste compost, ultra-high temperatures (>70°C) should be maintained during the composting without having an inhibitory effect on maturity. This study investigated the influence of bulk density (part 1) and easily-degraded organic matter content (EDOMC, part 2) on temperature evolution during vegetable waste composting: Part 1: corn straw with different particle sizes was used to achieve different bulk densities in the composting material (BD1-BD3); Part 2: partial or total substitution of the corn straw by corn starch was carried out to obtain different EDOMC (ED1-ED4). The composting experiments were conducted in a lab-scale reactor (1.75kg material) and lasted for 30d. Temperature and CO₂ emission were recorded daily, and the organic matter, lignocellulose, microbial activity, germination index (GI) and C/N of the samples were measured at different stages. The highest temperature (65.7°C) in part 1 occurred in the treatment with the bulk density of 0.35g/cm³, which also had the longest thermophilic phase. Bulk density was found to seriously influence the utilization efficiency of O₂ and heat transfer through materials, rather than heat production from organic matter degradation. In experiment part 2, the highest temperature was obtained with EDOMC of 45% (71.4°C). Therefore, adjusting the bulk density to 0.35g/cm³ and the easily-degraded organic matter content of the initial material to 45% was the best combination for reaching temperatures above 70°C during composting, with no inhibitory effect on the maturity of the compost product.

Keywords: 70°C; Bulk density; Compost; Cucumber stalk; Easily-degraded organic matter content; Vegetable waste.