From waste to resource: a multidimensional analysis of sewage sludge thermochemical treatment efficiency across temperatures†

Sewage sludge (SS) thermochemical treatment is considered as an effective management scheme in the transition to low carbon and sustainable development from conventional SS treatment. According to temperature and atmosphere, SS thermochemical treatment technologies are primarily categorized into thermal hydrolysis (TH), medium-temperature pyrolysis carbonization (MPC), high-temperature pyrolysis carbonization, gasification incineration, and incineration. Herein, the life cycle assessment (LCA), energy efficiency analysis (EEA), and cost–benefit analysis (CBA) methods were used to examine the environmental, energy, and economic performances of the five different SS thermochemical technologies. The LCA results indicate that MPC is environmentally favorable, with incineration being the most impactful in terms of environmental burden, MPC has a global warming potential (GWP) index of 163.63 kg CO₂ eq., significantly lower than the 306.37 kg CO₂ eq. impact generated by incineration. The EEA results show that the energy recovery rate increases with the temperature of thermochemical treatment. Economically, MPC has the best economic benefits, the CBA and environmental-CBA results are 97.39 and 87.17 RMB per tonne, respectively. Ultimately, scenario analyses illustrate that technological improvements by adding inorganic–organic separation pretreatment before MPC are beneficial to the reduction of environmental indicator values, especially by up to 42.48–44.21% in terms of ecological and human health hazards, with an additional economic benefit of 10.22%.