High Rate Composting with Innovative Process Control

Abstract

Despite the variety of composting plants present on the market, the design and operation of composting systems to improve the rate of the process and quality of end products are still an objective that has not been achieved. The composting process evolves through a thermophilic phase followed by a mesophilic one. The metabolism of microorganisms involved in the process is deeply disturbed by environmental changes like temperature, oxygen level and moisture. The aim of this study was to carry out a composting process in two separate reactors: the first, only in the thermophilic phase, with the purpose of pathogen destruction and decomposition by selected thermophilic microorganisms; the second, only in the mesophilic phase, to perform the main microbial transformations with a higher rate of volatile solids destruction. The results confirmed that maintaining constant the main parameters which affect the process, the microbial activity is enhanced. In the two-phase process, the evolution of parameters like moisture, organic carbon, humified organic matter, organic N, C/N and germination index (phytotoxicity) is more rapid relative to the single phase process. Also pathogen destruction is improved with the complete elimination of Faecal coliforms and Enterobacteriaceae and with a stronger reduction of Faecal streptococci.