Characterization of fine fraction mined from two Finnish landfills.

A fine fraction (FF) was mined from two Finnish municipal solid waste (MSW) landfills in Kuopio (1- to 10-year-old, referred as new landfill) and Lohja (24- to 40-year-old, referred as old landfill) in order to characterize FF. In Kuopio the FF (<20mm) was on average 45±7% of the content of landfill and in Lohja 58±11%. Sieving showed that 86.5±5.7% of the FF was smaller than 11.2mm and the fraction resembled soil. The total solids (TS) content was 46-82%, being lower in the bottom layers compared to the middle layers. The organic matter content (measured as volatile solids, VS) and the biochemical methane potential (BMP) of FF were lower in the old landfill (VS/TS 12.8±7.1% and BMP 5.8±3.4 m(3)CH4/t TS) than in the new landfill (VS/TS 21.3±4.3% and BMP 14.4±9.9 m(3)CH4/t TS), and both were lower compared with fresh MSW. In the Kuopio landfill materials were also mechanically sieved in the full scale plant in two size fraction <30 mm (VS/TS 31.1% and 32.9 m(3)CH4/t TS) and 30-70 mm (VS/TS 50.8% and BMP 78.5m(3)CH4/t TS). The nitrogen (3.5±2.0 g/kg TS), phosphorus (<1.0-1.5 g/kg TS) and soluble chemical oxygen demand (COD) (2.77±1.77 kg/t TS) contents were low in all samples. Since FF is major fraction of the content of landfill, the characterization of FF is important to find possible methods for using or disposing FF mined from landfills.