Pollution caused by antibiotics has brought significant challenges to the ecological environment. To improve the efficiency of the removal of tetracycline (TC) from aqueous solutions, a composite material consisting of TiO₂ and phosphoric acid-treated peanut shell biochar (p-BC) has been successfully synthesized in the present study by the sol-gel method. In addition, the composite material was characterized using various techniques, including scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) spectroscopy, X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy, and ultraviolet–visible diffuse reflectance spectroscopy (UV-vis DRS). The XPS and FTIR analyses revealed the formation of a new Ti–O–C bond, while the XRD analysis confirmed the presence of TiO₂ (with an anatase phase) in the composite material. Also, the PL analyses showed a notable decrease in the recombination efficiency of electrons and holes, which was due to the formation of a composite. This was further supported by the UV-vis DRS analyses, which revealed a decrease in bandgap (to 2.73 eV) of the composite material and led to enhanced light utilization and improved photocatalytic activity. Furthermore, the effects of pH, composite dosage, and initial concentration on the removal of TC were thoroughly examined, which resulted in a maximum removal efficiency of 95.3% under optimal conditions. Additionally, five consecutive cycle tests demonstrated an exceptional reusability and stability of the composite material. As a result of the experiments, the active species verified that ·O₂⁻ played a key role in the photodegradation of TC. Four possible degradation pathways of TC were then proposed. As a general conclusion, the TiO_2/p–BC composite can be used as an efficient photocatalyst in the removal of TC from aqueous solutions.

Livestock wastewater reuse could be a potential source for the distribution of antibiotics, antibiotic resistance bacteria (ARB), and antibiotic resistance genes (ARGs) in agricultural soil. In this study, soil samples were collected from different depths (0–60 cm) of farmland that has been subjected to long-term application of livestock wastewater. The vertical distribution of antibiotics, bacterial communities, and ARGs were assessed to identify the driving factors that could potentially influence the distribution of ARB and ARGs. The results demonstrated distinguished distributions of antibiotics along the soil depths, with tetracyclines (TCs) mainly found in the top 10 cm of the soil (0.11–0.31 μg/kg), while quinolones (QNs), sulfonamides (SAs), and macrolides (MLs) were detected in all 60 cm of soil depth (0.01–0.22 μg/kg). The selection pressure of antibiotics to microorganisms led to the proliferation of ARB, especially tetracycline-resistant bacteria and erythromycin-resistant bacteria. In terms of the distribution/abundance of ARGs, novA and tetA (58) were relatively higher in 0–10 cm surface soil, while vanRM and vanRF were mainly detected in the deeper soil. Different ARGs may have the same host bacteria, which lead to the emergence of multidrug resistant bacteria, such as Ilumatobacter sp., Aggregatilinea sp., Rhabdothermincola sp., and Ornithinimicrobium sp. Soil pH, electrical conductivity (EC), and moisture content (MC) could affect the distribution and proliferation of ARB and were found negatively correlated with most of the ARGs except macB. Therefore, it is potentially possible to eliminate/inhibit the spread of ARGs by adjusting these soil parameters. These findings provide insights into the distribution and dissemination of antibiotics, ARB, and ARGs in agricultural practices of livestock wastewater irrigation and provide effective mitigation strategies to ensure the safe use of livestock wastewater in agriculture.

The overuse of antibiotics has resulted in the prevalence of antibiotic resistance genes (ARGs) and antibiotic resistance bacteria (ARB) in the environment. High-density livestock farming is one of the major industries for antibiotic overuse. In this study, we sampled wastewater and manure at different stages of the feces treatment process from a dairy farm, as well as the soil in the farmland where the treated wastewater was being used for irrigation purpose. High-throughput Illumina sequencing was used to analyze the profiles of bacteria communities and ARGs. The results showed that the main ARG types were multidrug, aminoglycoside, glycopeptide, and tetracycline resistance genes, and Actinobacteria, Proteobacteria and Firmicutes were the main host bacteria phyla of these ARGs. The genus Nocardioides sp. and Ornithinimicrobium sp. were closely associated with the ARGs in the investigated samples. The relative abundances of ARGs in wastewater and manure were reduced by 68.5% and 62.1%, respectively, by the existing feces treatment process. Anaerobic fermentation and high-temperature fermentation were the most efficient treatment steps; the relative abundances of ARGs were reduced by 29.3% and 33.6% in the treated wastewater and manure, respectively. Irrigation with the treated wastewater significantly increased the abundance and diversity of ARGs and ARB in the surface soil of the farmland. The residual ARGs were found to transit through vertical gene transfer (VGT) and horizontal gene transfer (HGT) in soil. Therefore, the direct application of this inadequately treated wastewater and/or manure could risk spreading ARGs into the environment, and potentially impact human health. In order to effectively restrain the spread of ARGs, it is necessary to modify the wastewater and manure treatment processes and improve the regulations and guidelines of applying treated wastewater for irrigation.