Elimination of antibiotic resistance genes in waste activated sludge by persulfate treatment during the process of sludge dewatering.

Two sludge conditioning modes (nanoscale zero valent iron modified by Ginkgo biloba L. leaf (G-nZVI)/sodium persulfate (PS) conditioning with different ratios (1:0, 1:0.1, 1:1 and 1:10) and G-nZVI/PS conditioning with continuous addition) in reducing the specific resistance of filtration (SRF) and removing antibiotic resistant genes (ARGs) were investigated. After 3 min, the SRF values decreased in following order: 2.45 × 108 m/kg (1:10) > 5.95 × 106 m/kg (1:0.1) > 3.72 × 106 m/kg (1:0) > 4.92 × 105 m/kg (1:1). In the continuous addition (1:1), the SRF value decreased from 1.04 × 108 m/kg to 6.47 × 106 m/kg at 9 min. Removal efficiency of ARGs was 2-6 orders of magnitude and no regeneration of ARGs was observed in sludge and water phase. When treated samples were incubated for 36 h, dominant microflora was negatively correlated with ARGs. This study revealed persulfate treatment could achieve dewatering and remove ARGs, simultaneously.

Sulfidated nanoscale zero-valent iron is an efficient material for the removal and regrowth inhibition of antibiotic resistance genes.

Antibiotic resistance genes (ARGs) and mobile gene elements (MGEs), the emerging genetic contaminants, are regarded as severe risks to public health for impairing the inactivation efficacy of antibiotics. Secondary effluents from wastewater treatment plants are the hotspots for spreading these menaces. Herein, sulfidated nanoscale zero-valent iron (S-nZVI) was occupied to remove ARGs and MGEs in secondary effluents and weaken the regrowth capacity of their bacterial carriers. The effects of S/Fe molar ratios (S/Fe), initial pH and dosages on 16S rRNA and ARGs removal were also investigated. Characterization, mass balance and scavenging experiments were conducted to explore the mechanisms of the gene removal. Quantitative PCR (qPCR) and high throughput fluorescence qPCR showed more than 3 log unit of 16S rRNA and seven out of 10 ARGs existed in secondary effluent could be removed after S-nZVI treatment. The mechanisms might be that DNA accepted the electron provided by the Fe0 core of S-nZVI after being adsorbed onto S-nZVI surface, causing the decrease of 16S rRNA, ARGs and lost their regrowth capacity, especially for typical MGE (intI1) and further inhibiting the vertical gene transfer (VGT) and intI1-induced horizontal gene transfer (HGT). Fe0 core was oxidized to iron oxides and hydroxides at the same time. High throughput sequencing, network analysis and variation partitioning analysis revealed the complex correlations between bacteria and ARGs in secondary effluent, S/Fe could directly influence ARGs variations, and bacterial genera made the greatest contribution to ARGs variations, followed by MGEs and operational parameters. As a result, S-nZVI could be an available reductive approach to deal with bacteria and ARGs.

Simultaneous adsorption and degradation of triclosan by Ginkgo biloba L. stabilized Fe/Co bimetallic nanoparticles.

Triclosan (TCS), an antimicrobial agent added in many pharmaceutical and personal care products, can cause some environmental problems due to its bioaccumulation, toxicity and potential antibiotic cross-resistance. In this study, Ginkgo biloba L. leaf extract was used as the green stabilizing agent to synthesize Fe/Co bimetallic nanoparticles (G-Fe/Co NPs), which were applied to remove TCS from aqueous solution. G-Fe/Co NPs were characterized by TEM, EDS, SEM, BET, FTIR, XRD and XPS. G. biloba L. leaf extract improved the dispersion and reduced the passivation of NPs. The TCS removal efficiency followed the order of G-Fe/Co NPs > G-Fe NPs > Co NPs > Fe/Co NPs > Fe NPs. G-Fe/Co NPs can be reused at least eight times. The Co leaching under different initial pH values was negligible. The factors affecting the TCS removal were investigated. The results indicated that the removal of TCS followed pseudo-second-order kinetics, and the removal rate constant decreased with increasing the initial pH value and the initial TCS concentration, and decreasing the Co loading of G-Fe/Co NPs and NPs dosage. The mass balance of TCS removal by G-Fe/Co NPs indicated that adsorption was dominant process and TCS degradation was an accumulative process.