Stabilizate from Autoclaved Municipal Solid Waste as a Source of Valuable Humic Substances in a Waste Circular Economy

Abstract One of the solutions in unsorted municipal waste management is autoclaving, which maximize the amount of waste for recycling. After autoclaving, however, up to 30% of autoclaved waste, called organic remaining fraction (ORF) is still unstabilized and cannot be landfilled but must be subjected for further stabilization, e.g. in aerobic conditions. After this process waste meets standards for landfilling. However, as during aerobic stabilization humification of organic matter proceed, before landfilling humic substances (HS) could be recovered. High HS concentration in ORF means that before its landfilling HS can be recovered. The maximal recovering of valuable substances from waste is in line with the principles of sustainable development. Therefore, this study examined the humification of ORF from a full-scale mechanical-heat-treatment plant during composting in two-stage system (1st stage in 550 L reactor, 2nd stage in windrow). The rates of organics mineralization were 8.35–12.00 g OM/kg d.m. d. The rates of HS formation were lower, 3.31–3.92 mg/g OM d, and process proceeded most intensively up to 50 days. The maximum HS concentrations were 82–120 mg/g OM, similar to those in composts from different kinds of organic waste. Graphic Abstract