Stabilization of heavy metals in piggery wastewater sludge through coagulation-hydrothermal reaction–pyrolysis process and sludge biochar for tylosin removal

Abstract Piggery wastewater sludge is rich in organic matter but contains pollutants that are harmful to the environment and ecology, such as heavy metals. In this paper, a novel process for hazard-free treatment and resource utilization of piggery wastewater sludge was proposed. Technique combining Fe(II) coagulation, hydrothermal reaction and pyrolysis (CHP) was used to stabilize heavy metals (HMs) in sludge, and the adsorption performance of the recycled product to tylosin (TYL) was studied. SV30 (Sludge Volume 30 min) of sludge decreased from 97% to 30% after Fe(II) coagulation and water content of sludge decreased from 97% to 30% after hydrothermal treatment. After CHP treatment, the residue fraction of Cd, Pb, Cu, Zn, Cr and Ni increased by 12.1%, 67.3%, 12.4%, 15.4%, 58.5%, 2.8% respectively. With raising Fe2+ dosage, residual state of each heavy metal increases. Sludge biochar (SBC) generated after CHP process is a kind of mesoporous composite composed of goethite, quartz, biochar and polymer, and showed a high adsorption capacity for tylosin, and the process of which can be well expressed by Langmuir adsorption isotherm (R2 = 0.947). The maximum theoretical adsorption capacity of SBC for TYL can be obtained by pyrolysis at 600 °C, which can reach 58 mg g−1.