The seawater dry water extinguishing materials formed by coating seawater with nano-SiO 2 have greatly enlarged the application space of the seawater as a fire-extinguishing medium. Against the deficiencies in the evaluation of the size-fractionated and stability of dry water extinguishing materials, especially of the coating effect of nano-SiO 2 , this study designed an airflow size-fractionated system applicable to dry water materials and characterized the stability of dry water materials by electrochemical methods according to the pneumatic separation principle. The results showed that the grain size range of seawater@nano-SiO 2 dry water extinguishing materials was 0.2–400 μm, and that the dry water could be divided into three intervals by granule size by adjusting the turbo-dynamo frequency and draught fan frequency of the airflow size-fractionated system. The electrochemical methods are applicable to describe the stability of the dry water extinguishing materials, and the gelatinization of core material can significantly make up for the deficiency that the core material of dry water tends to separate out over storage time. However, the stability of dry water is subject to granule size more than the gelatinization of the core material, and the dry water with big-size granules has optimal stability. Graded dry water is less corrosive to aluminum sheets, and the corrosion resistance to big-grained gel-dry water is optimal. The research conclusion can provide a technical basis for size-fractionated and covering effect characterization of dry water extinguishing materials and for type selection of storage media.
Kaifeng Yu,Peng Li,Yiliang He,Bo Zhang,Yihan Chen,Jinghan Yang
Serious concerns have been raised regarding antibiotic resistance genes (ARGs) with respect to their potential threat to human health. Wastewater treatment plants (WWTPs) have been considered to be hotspots for ARGs. In this study, high-throughput quantitative polymerase chain reaction (HT-qPCR) was used to profile size-dependent ARGs and mobile genetic elements (MGEs) divided by particle-associated (PA) assemblages (>3.0-μm), free-living (FL) bacteria (0.2 - 3.0-μm) and cell-free (CF) DNA (< 0.2-μm) in two full-scale WWTPs (plants A and B) and a receiving stream. The results revealed that FL-ARGs were predominant in WWTPs and the receiving stream, especially in the final effluent of both plants. More than 40 types of CF-ARGs and CF-MGEs were detected with absolute abundances ranging from 6.0 ± 0.7 × 10 5 to 1.0 ± 0.2 × 10 8 copies/mL in wastewater, and relatively high abundances were also detected in the final effluent of the two plants, suggesting that CF-ARGs were important sources spreading from the WWTPs to the receiving environment. Plant A exhibited higher log-removal of size-fractionated ARGs and MGEs than was observed for plant B, which was attributed to the enhanced settleability of PA assemblages and FL bacteria by additional macrophytes and chemical coagulants. Ultraviolet disinfection had limited effects on ARGs and MGEs of the PA and FL fractions, which was probably ascribed to the protective matrices of the particles and cell walls. The bacterial communities of the two plants were significantly different among the size fractions ( p < 0.01). The variation partitioning analysis (VPA) indicated that the microbial community structures and MGEs contributed a variation of 68.2% in total to the relative abundance changes of size-fractionated ARGs. Procrustes analyses and Mantel tests showed that the relative abundances of ARGs were significantly correlated with bacterial community structures. These results suggested that the bacterial community structures and MGEs might have been the main drivers of the size-fractionated ARG disseminations. This study provides novel insights into size-fractionated ARGs and MGEs in full-scale WWTPs and may lead to the identification of key targets to control the spread of ARGs.
危险品化学品经营许可证（带存储）