Composting is a potential alternative for cephalosporin C fermentation dregs (CCFDs) compared with incineration process or landfill because of its advantage of recovering nutrients. In this research, CCFDs and activated sludge (AS) were co-composted to analyze the feasibility of recycling the nutrients in CCFDs. A pilot-scale aerobic composting system with an auto-control system was used in this research, and the maturity and security of the compost product were evaluated. The temperature of the composting mixtures was maintained above 55°C for more than 3 days during the composting, indicating that co-composting of CCFDs and AS could reach the compost maturity standard, and the seeds germination index (GI) increased from 17.61% to 68.93% by the end of the composting process (28 days). However, the degradation rate of cephalosporin C (CPC) was only 6.58% during the composting process. Monitoring the quality of antibiotic resistance genes (ARGs) in the composts showed that the log copy of blaTEM in the composts increased from 2.15 in the initial phase to 6.37 after 28 days. Long-term investigation of CPC degradation and ARGs variation was conducted for the composts; CPC could still be detected after the maturity phases. A removal efficiency of 49.10% could be achieved in 110 days, while the log copy of ARGs increased to 7.93. Although a higher GI value (>80.00%) was observed, the risk of recycling the CCFDs compost product into land is still high.

Wastewater recycling technologies have been widely used in tanneries to reduce environmental impacts. However, only a few recycling methods have been developed for vegetable tanning processes due to limited knowledge of their wastewaters. In this study, the structures of the polyphenols in the larch tanning wastewater (LTW) and commercial larch tannin (CLT) were characterized with spectrographic and chromatographic analysis. Structures of these polyphenols were illustrated accordingly; their collagen reaction abilities were then tested with thermal analysis and visualized with a molecular docking software. Results showed that polyphenols in LTW and CLT were all procyanidins. However, average molecular weight of the polyphenols in LTW was 1104Da, in contrast to an obviously higher value for the CLT sample (3334Da). Meanwhile, the LTW presented obvious lower reactivity in the collagen-polyphenol reaction, including lower thermal stabilities and docking energies, fewer hydrogen bonds, and lower interaction energies. These results provide a hint for vegetable tanning wastewater recycling: because of these structural differences, reactivity of the polyphenols in wastewater are lower than the ones in commercial tannins. Therefore, before the recycling processes, polyphenols must be chemically modified in accordance with these structural differences.