Combined addition of bagasse and zeolite stabilizes potentially toxic elements in sewage sludge compost and improves Eucalyptus urophylla seedling growth

[Display omitted] •Stability of co-compost on potential toxic elements (PTEs) in sludge was studied.•Co-composting of sludge + zeolite + bagasse (BZSC) reduced PTEs content and mobility.•Stabilization of PTEs in BZSC remained for an extended duration in forestland soil.•Adding BZSC promoted the growth of Eucalyptus urophyllus seedlings. Potentially toxic elements (PTEs) including Cu, Zn, Pb, Cd and Ni in sewage sludge compost (SSC) are important obstacles to SSC forestry utilization. Synergistic fixation of bulking agent and adsorbent may shed new light on solving the problem for stabilization of PTEs in SSC before forestry disposal. The aim of this study was to investigate whether bulking agent (bagasse) + adsorbent (zeolite) can be integrated into forestry utilization processes of SSC. First, stabilization of PTEs in SSC were compared to those of composted bagasse + sewage sludge (BSC), zeolite + sewage sludge (ZSC) and bagasse + zeolite + sewage sludge (BZSC) after 60 days of composting. Subsequently, the long-term stability of PTEs in different composts-amended soil was monitored in a 2-year field trial on Eucalyptus urophylla forestland. Finally, a 12-month pot experiment was carried out to investigate their effects on the growth of Eucalyptus urophylla seedlings and PTEs absorption. Compared with SSC, addition of bagasse and zeolite significantly decreased total and extractable PTEs concentration and increased residual fractions in compost. In the field experiment, the total and extractable fraction concentrations of PTEs in topsoil after BZSC application were significantly lower than those after SSC and BSC application, and the status kept unchanged during the 2-year trial period. In the pot experiment, we further found that, compared with SSC, BSC and ZSC addition in the cultivated soil, the addition of BZSC promoted significantly greater growth and reduction in PTEs concentrations in Eucalyptus urophylla seedlings. Our results indicate that the combined addition of bagasse and zeolite can stabilize PTEs in SSC for an extended duration, improve plant growth, and therefore enhance the potential of sewage sludge compost utilization in forestry.