The effect of isosaccharinic acid (ISA) on the mobilization of metals in municipal solid waste incineration (MSWI) dry scrubber residue

Abstract

Co-landfilling of incineration ash and cellulose might facilitate the alkaline degradation of cellulose. A major degradation product is isosaccharinic acid (ISA), a complexing agent for metals. The impact of ISA on the mobility of Pb, Zn, Cr, Cu and Cd from a municipal solid waste incineration dry scrubber residue was studied at laboratory using a reduced 2 5−1 factorial design. Factors investigated were the amount of calcium isosaccharinate (Ca(ISA) 2), L/ S ratio, temperature, contact time and type of atmosphere (N 2, air, O 2). The effects of pH and Ca(ISA) 2 as well as other factors on the leaching of metals were quantified and modelled using multiple linear regression ( α = 0.05). Cd was excluded from the study since the concentrations were below the detection limit. The presence of Ca(ISA) 2 resulted in a higher leaching of Cu indicating complex formation. Ca(ISA) 2 alone had no effect on the leaching of Pb, Zn and Cr. A secondary effect on the mobilization was predicted to occur since Ca(ISA) 2 had a positive effect on the pH and the leaching of Pb, Zn and Cr increased with increasing pH. The leaching of Pb varied from 24 up to 66 wt.% of the total Pb amount (1.74 ± 0.02 g(kg TS) −1) in the dry scrubber residue. The corresponding interval for Zn (7.29 ± 0.07 g(kg TS) −1) and Cu (0.50 ± 0.02 g(kg TS) −1) were 0.5–14 wt.% of Zn and 0.8–70 wt.% of Cu. Maximum leaching of Cr (0.23 ± 0.03 g(kg TS) −1) was 4.0 wt.%. At conditions similar to a compacted and covered landfill (4 °C, 7 days, 0 vol.% O 2) the presence of ISA can increase the leaching of Cu from 2 to 46 wt.% if the amount of cellulose-based waste increases 20 times, from the ratio 1:100 to 1:5. As well, the leaching of Pb, Zn, and Cr can increase from 32 to 54 wt.% (Pb), 0.8–8.0 wt.% (Zn), and 0.5 to 4.0 wt.% (Cr) depending on the amount of cellulose and L/ S ratio and pH value. Therefore, a risk ( α = 0.05) exists that higher amounts of metals are leached from landfills where cellulose-containing waste and ash are co-disposed. This corresponds to an additional 29 t of Pb and 17 t of Cu leached annually from a compacted and covered landfill in the north of Sweden.