Pile settlement and volume reduction measurement during forced-aeration static composting

In this study, a settlement measurement device was used to track the settlement of different layers in composting piles, and time courses of settlement velocity, bulk density distribution, and effective bulk density were investigated. Settlement is divided into two stages: the physical compressive settlement and the mass loss settlement. At the end of the former stage, bulk density (ρ′) and pile height (h) follow ρ′ = AhB, where A is a fitting parameter for the initial bulk density of the composting material, and B is the compression parameter. The physical compressibilities of composting mixtures are night-soil sludge and garden refuse (1:1) > sewage sludge and cornstalks (5:4) > night-soil sludge and garden refuse (2:3) > sewage sludge and bark (1:1). Adding the proportion of bulking agent in the proper extent effectively retarded composting settlement. Bark exhibits a better supporting capability than cornstalk does as a bulking agent.