Short- and Long-Term Compressibility Properties of Biologically (Biodried) and Mechanically Treated Municipal Solid Waste: A Case Study of BMT Plant in Marišćina, Croatia

Biodrying is a variation of the aerobic degradation process that partially stabilizes raw municipal solid waste by reducing its initial moisture content and the amount of easily degradable components. It is a short-term process which lasts up to 14 days. After 14 days of biodrying, MSW is submitted for further mechanical processing, after which recyclable materials (metals, glass, and plastics), refuse-derived fuel, and reject waste stream are separated. Although biologically treated, reject waste stream (biodried waste) still contains a significant amount of organic content, which supports its disposal into the so-called bioreactor landfill. In order to enhance the degradation process and production of landfill gases, the biodried waste deposited within the bioreactor landfill is subjected to the wetting process immediately after the landfill cell achieves its design height. Clearly, the wetting process, coupled with the degradation and production of landfill gases, can cause the additional settlement of the landfill body. Thus, in order to estimate the total settlement of the landfill body and, consequently, the landfill capacity, the short- and long-term compressibility properties of the biodried waste must be identified. In the present research, the settlement caused by the degradation process of the biodried waste and production of landfill gases was studied using the long-term oedometer test. In addition, three short-term oedometer tests were performed on dry, wet, and initially dry and subsequently wetted biodried waste samples. In experiments, the immediate, secondary, and bio-induced compression indexes of biodried waste were obtained. Based on the experimental results, the functional relationship between the immediate compression index and void ratio valid for biodried waste is proposed. Finally, the conceptual time–settlement model applicable to the bioreactor landfills, which accept biodried waste, is also proposed. Graphical Abstract