Cross-sectoral synergy between municipal wastewater treatment, cement manufacture and petrochemical synthesis via clean transformation of sewage sludge†
The municipal wastewater treatment sector requires sustainable management of sewage sludge to fundamentally contribute to building zero-waste cities. Herein, we propose an integrated material-flow strategy to make full use of sewage sludge by combining its clean transformation with cement manufacture and petrochemical synthesis. Based on the multi-stage thermochemical conversion process which could effectively reduce the emission of carbonaceous pollutants, the organic components in sludge are converted to syngas with tunable H2/CO molar ratios, while the remaining inorganic components are used to prepare eco-friendly cement clinkers. Under the conditions investigated in this study, 8.9 kmol of syngas with a gross H2/CO molar ratio of 1.7 and 1.9 tonnes of cement clinkers with a sludge-ash replacement ratio of 30.9% can be produced from one tonne of dried raw sewage sludge. The proposed strategy allows sewage sludge to be an alternative feedstock, partially replacing natural resources, to produce petrochemicals and cementitious materials, offering a new pathway to cross-sectoral synergy among municipal wastewater treatment, cement manufacture and petrochemical synthesis.