Heavy metals in source-separated compost and digestates

• Published in: Waste management (Elmsford) Vol. 34; no. 5; pp. 867 - 874
• Main Authors: Kupper, Thomas, Bürge, Diane, Bachmann, Hans Jörg, Güsewell, Sabine, Mayer, Jochen
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.05.2014; Elsevier
• Subjects: Anaerobic digestion; Applied sciences; Bio-waste; Exact sciences and technology; Fertilizer; Green waste; Heavy metals; Mass loads; Metals, Heavy - analysis; Other wastes and particular components of wastes; Pollution; Soil Pollutants - analysis; Solid Waste - analysis; Switzerland; Wastes; Switzerland; Mass loads; Bio-waste; Green waste; Anaerobic digestion; Heavy metals; Fertilizer; Compost; Organic matter; Pollution; Statistical analysis; Fertilization; Regional scope; Lead; Agricultural soil; Farmyard manure; Material balance; Fertilizers; Heavy metal
• ISSN: 0956-053X; 1879-2456
• DOI: 10.1016/j.wasman.2014.02.007

•Heavy metals were analyzed in compost/digestate from source-separated organic waste.•The concentrations were mostly below legal thresholds but some high values occurred.•Contamination was driven by factors other than treatment process or input materials.•At regional scale, composts and digestates induce minor heavy metal loads to soils. The production of compost and digestate from source-separated organic residues is well established in Europe. However, these products may be a source of pollutants when applied to soils. In order to assess this issue, composts, solid and liquid digestates from Switzerland were analyzed for heavy metals (Cd, Co, Cr, Cu, Ni, Pb and Zn) addressing factors which may influence the concentration levels: the treatment process, the composition, origin, particle size and impurity content of input materials, the season of input materials collection or the degree of organic matter degradation. Composts (n=81) showed mean contents being at 60% or less of the legal threshold values. Solid digestates (n=20) had 20–50% lower values for Cd, Co, Pb and Zn but similar values for Cr, Cu and Ni. Liquid digestates (n=5) exhibited mean concentrations which were approximately twice the values measured in compost for most elements. Statistical analyses did not reveal clear relationships between influencing factors and heavy metal contents. This suggests that the contamination was rather driven by factors not addressed in the present study. According to mass balance calculations related to Switzerland, the annual loads to agricultural soils resulting from the application of compost and digestates ranged between 2% (Cd) and 22% (Pb) of total heavy metal loads. At regional scale, composts and digestates are therefore minor sources of pollution compared to manure (Co, Cu, Ni, Zn), mineral fertilizer (Cd, Cr) and aerial deposition (Pb). However, for individual fields, fertilization with compost or digestates results in higher heavy metal loads than application of equivalent nutrient inputs through manure or mineral fertilizer.