Process characteristics of hydrothermal treatment of antibiotic residue for solid biofuel

•Hydrothermal treatment (HT) was performed for two kinds of antibiotic residues (ARs).•HT greatly improved the dewaterability of solid matters to produce biofuel at about 50% solid recovery ratio.•HT transferred more than 50% nitrogen in solid matters of AR into liquid of HT process.•HT almost completely decomposed the residual antibiotics in AR.•The liquid from HT has high COD to be potentially suitable for anaerobic digestion. Hydrothermal treatment (HT) of environmentally and healthily hazardous antibiotic residue (AR) was performed in a laboratory batch autoclave to investigate the feasibility of solid biofuel production and to understand some characteristics of the HT process. The results showed that HT remarkably improved the dewaterability of the tested residues. For ARa with a lower content of saccharides, the optimal HT conditions were shown to be at 200°C for 30min, under which a solid biofuel with a water content of 47.6wt.% was obtained at a solid recovery ratio of 42.5%. For ARb with a higher content of saccharides, a lower optimal HT temperature of 180°C was required, to attain a similar solid content but at a lower solid recovery ratio. The nitrogen content in the solid biofuel from ARa was lowered to 5.8wt.%, implying 68% removal of nitrogen from the solid of the raw residue. The removed nitrogen was mostly transferred into the HT liquid as ammonia nitrogen. Additionally, almost all the antibiotics in the tested ARs were decomposed during HT. Hydrothermal technology was thus proved to be promising for recycling ARs to make clean bioenergy and meanwhile to realize the thorough safe treatment of ARs.