Co-hydrothermal carbonization of sewage sludge and polyvinyl chloride: Hydrochar properties and fate of chlorine and heavy metals

An efficient method of synergetic dechlorination and reduction of heavy metals risk is crucial for the clean resource utilization of sewage sludge (SS) and polyvinyl chloride (PVC). In this work, SS was upgraded to hydrochar using co-hydrothermal carbonization (HTC) with PVC at different mixing ratio (30─70%) at 230 °C. Transformation behaviors of chlorine and heavy metals in hydrochars, along with fuel properties, were evaluated. The results illustrated that Mn and Zn could be effectively removed during co-HTC and low ratio addition of PVC was beneficial for reducing the toxicity of Ni and As. Meanwhile, compared with the HTC of single PVC, co-HTC with SS could further improve the dechlorination efficiency (69.49─81.35%). Particularly, the blending ratio of SS to PVC at 7:3 showed high fuel ratio and HHV (13.58   MJ/kg) with desirable combustion performance. These findings offered a potential approach to convert SS and PVC into clean solid fuel.