Life cycle assessment of sludge anaerobic digestion combined with land application treatment route: Greenhouse gas emission and reduction potential

Sewage sludge treatment and disposal is essential for water environment protection and pollution management. Coupling anaerobic digestion with land application offers a promising solution to recycle energy and resources to reduce greenhouse gas(GHG) emissions. However, the comprehensive assessment of the anaerobic digestion treatment route on GHG emissions and reduction potential is lacking. This study used life cycle assessment(LCA) to evaluate the GHG emissions based on two cases. The GHG emissions resulting from the digested sludge land application was considered, and the reduction potentials resulting from biogas utilization and substituting chemical fertilizers were also analyzed. The results showed the net GHG emissions of the two cases were 178.92 and -26.33 kg CO2-eq/tDS, respectively. When excluding the reduction, the GHG emissions of the two cases were 519.32 and 352.97 kg CO2-eq/tDS, respectively, where the dewatering, digested sludge drying, and land application were the main contributors. The GHG emissions associated with the digested sludge land application accounted for 28% and 45% of the total GHG emissions in two cases, respectively. The GHG emission reduction could be achieved by sludge substitution for chemical fertilizer, which could offset 65.5% and 107.5% of the total GHG emissions in two cases, respectively. While the biogas utilization could only offset less than 10% of the total GHG emissions of both cases. Likewise, improving organic content or specific biogas yield rates could only offset up to 26.2% and 40.3% of the total GHG emissions. These findings provide understanding into evaluating GHG emissions of the sludge anaerobic digestion treatment route.

Automated summary

Sewage sludge treatment and disposal are crucial for water environment protection and pollution management. This study used life cycle assessment to evaluate the greenhouse gas emissions and reduction potential of anaerobic digestion treatment. The results showed that sludge drying and land application were the main contributors to greenhouse gas emissions. Sludge substitution for chemical fertilizer could effectively reduce greenhouse gas emissions, while biogas utilization had a limited impact.