The influence of biological stabilisation of the undersize fraction of municipal solid waste on the energy parameters of the stabilizer

According to Polish law, the undersized fraction of mixed municipal solid waste (MSW) requires six-week biological stabilisation, usually involving aerobic treatment due to operating and investment costs. However, the low efficiency of sorting high-energy materials from mixed waste implies that they may still meet the energy recovery conditions, even if a significant mass of organic matter is removed during the process. This study, therefore, aimed to assess the energy potential changes of bio-stabilizate during aerobic treatment on a technical scale. Freshly sieved mixed MSW had a relatively low lower heating value (LHV) of 4.16 MJ/kg, considered insufficient for autothermic incineration. Biological stabilisation significantly affects the energetic properties from the outset of treatment. After one week, the LHV, energy potential (EP) and electrical power potential (EPP) in the samples increased to 6.2 MJ/kg, 15.7 GWh and 197 MW per year, respectively. A similar high potentials were observed in the fifth week of treatment. Statistical analysis revealed that moisture was a key factor reducing the energy potential of the waste, whereas a high carbon, hydrogen and nitrogen content improved it. The maximum EP (>14 GWh) could theoretically be achieved at a carbon concentration of 50-60 % and a moisture of 28-40 %, whilst the maximum EPP (>180 MW) at a carbon content of 55-50 % and a moisture of 34-36 %. The N-rich samples also had increased EP and EPP; however, oxide emissions were not considered. Studies have shown that under certain conditions, the energy can still be effectively recovered from biostabilizate.