Innovative dual-step management of semi-aerobic landfill in a tropical climate

Despite concerted efforts to innovate the solid waste management (SWM) system, land disposal continues to represent the most widely used technology in the treatment of urban solid waste worldwide. On the other hand, landfilling is an unavoidable step in closing the material cycle, since final residues, although minimized, need to be safely disposed of and confined. In recent years, the implementation of more sustainable landfilling aims to achieve the Final Storage Quality conditions as fast as possible. In particular, semi-aerobic landfill appears to represent an effective solution for use in the poorest economies due to lower management costs and shorter aftercare resulting from aerobic stabilisation of the waste. Nevertheless, the implementation of a semi-aerobic landfill in a tropical climate may affect the correct functioning of the plant: a lack of moisture during the dry season and heavy rainfalls during the wet season could negatively affect performance of both the degradation process, and of leachate and biogas management. This paper illustrates the results obtained through the experimentation of a potential dual-step management of semi-aerobic landfilling in a tropical climate in which composting process was reproduced during the dry season and subsequently flushing (high rainfall rate) during the wet period. Eight bioreactors specifically designed: four operated under anaerobic conditions and four under semi-aerobic conditions; half of the reactors were filled with high organic content waste, half with residual waste obtained following enhanced source segregation. The synergic effect of the subsequent phases (composting and flushing) in the semi-aerobic landfill was evaluated on the basis of both types of waste. Biogas production, leachate composition and waste stabilization were analysed during the trial and at the end of each step, and compared in view of the performance of anaerobic reactors. The results obtained underlined the effectiveness of the dual-step management evidencing how wastes reached a higher degree of stabilization and reference FSQ values for leachate were achieved over a one-year simulation period.