The effect of dry matter on the composting rate: Theoretical analysis and practical implication

As a result of temperature-based process control, composting material may become too dry and prevent sufficient compost stabilization. Management of the dry matter content is imperative, and information on the optimal dry matter content is needed. A relationship between dry matter content and the maximum Oxygen Uptake Rate (OUR) is derived from a mechanistic model of the process. The model shows that both the density and the structure of the waste influence the the optimum moisture level. The model explains the adverse effect of size reduction on the maximum OUR. This means that size reduction must be critically evaluated, together with the dry matter content, to avoid adverse substrate conditions. The model further implies that the optimum dry matter may change during the composting process, and this result matches our experimental observations. Monitoring the optimal dry matter content during biodegradation might offer a way to further optimize the composting process.