Differences in the mobility of Cd, Cu, Pb and Zn during composting of two types of household bio-waste collected in four seasons

•Two types of household bio-waste collected in four seasons were composted.•Composting decreased the exchangeable content of Cd, Cu, Pb and Zn by 50%.•The highest decline of availability was recorded in the thermophilic phase.•Residual fraction prevailed in the final compost.

The objective of this study was to evaluate the mobility of Cd, Cu, Pb and Zn during 3 different compost aeration rates of household bio-waste, originating in urban settlement (U-bio-waste) and family house buildings (F-bio-waste). The first two weeks, when the thermophilic composting phase became, the highest decline of exchangeable content was recorded. After 12 weeks of composting, lower exchangeable content was found in the case of U-bio-waste composts than F-bio-waste composts, despite higher loss of fresh mass. The order of fractions in both final composts was as follows: residual > oxidizable > reducible > exchangeable. The exchangeable portion of total content in final composts decreased in this order: Zn (17%), Cd (11%), Pb (4%) and Cu (3%). Regarding the low exchangeable content of heavy metals and high-quality organic matter, these types of composts could be used not only as fertilizer, but for remediation of metals contaminated land.