Assessment of co-composting of sludge and woodchips in the perspective of environmental impacts (EASETECH)

• Sludge and woodchip co-composting and utilization were assessed by LCA-model EASETECH.
• Co-composting impacts acidification and terrestrial eutrophication by ammonia release.
• Fewer woodchips decreased impacts to acidification and terrestrial eutrophication.
• Impacts to human toxicity are insignificant when using compost for urban landscaping.
• Trace odorous compounds impact marginally to global warming and toxicity categories.

To reveal potential impacts to environment and human health quantitatively, co-composting and utilization of sludge and woodchips were investigated using a life-cycle-based model, EASETECH. Three scenarios were assessed through experiments using different material ratios. Emission amounts during co-composting were determined by monitoring data and mass balance. With 100 t sludge treatment, co-composting showed impacts to acidification (29.9 PE) and terrestrial eutrophication (57.7 PE) mainly for ammonia emission. Compost utilization presented savings on freshwater eutrophication (−1.5 PE) because of phosphorus substitution. With the application of fewer woodchips, impacts to acidification and terrestrial eutrophication decreased because more ammonium was reserved rather than released. All impacts to human toxicity were not significant (8.2 ± 0.6 PE) because the compost was used for urban landscaping rather than farming. Trace gaseous compounds showed marginal impacts to global warming and toxicity categories. The results provide a new perspective and offer evidence for appropriate sludge treatment selection.