Antibiotic residues lead to the risk of resistance gene enrichment, which is the main reason why penicillin mycelial dreg (PMD) is defined as hazardous waste. Hydrothermal treatment (HT) is an effective method to treat penicillin mycelial dreg, but the degradation mechanism of penicillin is unclear. In the study, we researched the effects of pH (4–10) at 80–100 °C and metal ions (Mn2+, Fe2+, Cu2+, and Zn2+) at several concentrations on the HT of penicillin, identified the degradation products (DPs) under different conditions, and evaluated the antibacterial activity of hydrothermally treated samples. The results show that penicillin degradation kinetics highly consistent with pseudo-first-order model (R2 = 0.9447–0.9999). The degradation rates (k) at pH = 4, 7, and 10 were 0.1603, 0.0039, and 0.0485 min−1, indicating acidic conditions were more conducive to penicillin degradation. Among the four tested metal ions, Zn2+ had the most significant catalytic effect. Adding 5 mg·L−1 Zn2+ caused 100% degradation rate at pH = 7 after HT for 60 min. Six degradation products (DPs) with low mass-to-charge (m/z ≤ 335) were detected under acidic condition. However, only two and three DPs were observed in the samples catalyzed by Zn2+ and alkali, respectively, and penilloic acid (m/z = 309) was the main DPs under these conditions. Furthermore, no antibacterial activity to Bacillus pumilus was detected in the medium with up to 50% addition of the treated samples under acidic condition. Even though acid, alkali, and some metal ions can improve the degradation ability of penicillin, it was found that the most effective way for removing its anti-bacterial activity was under the acidic condition. Therefore, resistance residue indicates the amount of additive in the process of resource utilization, and avoids the enrichment of resistance genes.
Erythromycin is one of the most commonly used macrolide antibiotics. However, its pollution of the ecosystem is a significant risk to human health worldwide. Currently, there are no effective and environmentally friendly methods to resolve this issue. Although erythromycin esterase B (EreB) specifically degrades erythromycin, its non-recyclability and fragility limit the large-scale application of this enzyme. In this work, palygorskite was selected as a carrier for enzyme immobilization. The enzyme was attached to palygorskite via a crosslinking reaction to construct an effective erythromycin-degradation material (i.e., EreB@modified palygorskite), which was characterized using FT-IR, SEM, XRD, and Brunauer–Emmett–Teller techniques. The results suggested the successful modification of the material and the loading of the enzyme. The immobilized enzyme had a higher stability over varying temperatures (25–65 °C) and pH values (6.5–10.0) than the free enzyme, and the maximum rate of reaction (Vmax) and the turnover number (kcat) of the enzyme increased to 0.01 mM min−1 and 169 min−1, respectively, according to the enzyme-kinetics measurements. The EreB@modified palygorskite maintained about 45% of its activity after 10 cycles, and degraded erythromycin in polluted water to 20 mg L−1 within 300 min. These results indicate that EreB could serve as an effective immobilizing carrier for erythromycin degradation at the industrial scale.
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