查看更多>>摘要：Water quality management of sediment-laden rivers is a challenging issue for global water security because sediment is a major carrier for the migration and transformation of biogenic elements and pollutants in river systems. A water quality index (WQI) based on multiple parameters is widely used when making water quality assessments. To reduce the analytical costs and time required for multi-parameter measurements, many minimum WQI (WQI_(min)) models that rely on fewer key parameters are now being developed for river systems. However, no systematic study of WQI_(min) has been conducted yet in sediment-laden rivers, such as China's Yellow River which has the highest sediment concentration worldwide. This study assessed the spatiotemporal variation in water quality of the Yellow River's main channel in the spring and autumn of 2019. The WQI was calculated based on 15 water parameters determined at 44 sampling points from 26 river sections and six reservoirs. A heavy metal evaluation index (HEI) was used to gauge the pollution level of eight heavy metals. Despite no distinct seasonal variation, the WQI values decreased from the Yellow River's source region to its estuary, and higher values were observed in most reservoirs than in adjacent natural river sections. Values for WQI (>50) were mainly classified as being at "good" and "moderate" water quality levels, while the HEI values (<10) indicated a low pollution level. Four weighted and four non-weighted WQI_(min) models were developed using stepwise regression. A model consisting of six parameters-total suspended solids, ammonia-nitrogen, permanganate index, electrical conductivity, dissolved oxygen, and nitrate-nitrogen-had the best modeling performance. Both the prediction accuracy and goodness-of-fit of the WQI_(min) model were improved after adding parameter weights. Our study provides support data for water resource management in the Yellow River Basin, and contributes to the development of a robust WQI_(min) in sediment-laden rivers.
查看更多>>摘要：Nitrogen (N) and phosphorus (P) species in wastewater treatment plants (WWTPs) effluents are important sources of nutrient input to water bodies, resulting in deteriorated eutrophication. The combination of electrochemical technology and constructed wetland provides emerging prospects for tertiary treatment of WWTPs effluents. In this work, three bench-scale electrochemically integrated vertical flow constructed wetlands (E-VFCWs) were established in parallel with different inoculated sources. Among them, the E-VFCW inoculated with anaerobic sludge (AN) of a swine wastewater treatment plant exhibited significantly shorter start-up period (9 d), followed by anoxic sludge (A) from a municipal WWTP (18 d), and no inoculum (NI) exhibited the longest startup duration (30 d). In addition, AN group allowed the highest removal efficiencies (NO3-N (97.0 ±1.6 %), TN (83.3 ± 4.6 %), and PO4-P (93.3 ± 3.3 %)) in tertiary wastewater treatment, and lower concentrations of SO4~(2-)-S and total Fe in effluents. Results of microbial structure and Tax4Fun suggested that multi-path metabolisms including H_(2-), Fe(II)-, and FemSn-dependent denitrification might facilitate NO3-N reduction in E-VFCWs. The microbial mechanisms that AN exhibited the highest denitrification efficiency in the E-VFCWs may include the highest bacterial copies number and the more abundant denitrifying genes. Moreover, it should be noted that electron transfers mediated by sulfur (S) cycle might significantly enhance NO3-N reduction in E-VFCWs, especially in AN group. To conclude, the study offers new microbial insights into N conversion and S cycling patterns in electrochemically integrated systems in response to inoculated source.
查看更多>>摘要：A numerical model is developed for the minimum ignition energy (MIE) calculation of pure and mixture dust clouds, considering the influence of particle size distribution. The original particle number based size distribution is approximated with median sizes (number d_(50)) of the subdivisions obtained by dividing the original distribution range. The MIE is calculated for 5 pure dusts, 2 mixtures of combustible dusts and 2 mixtures of combustible & inert dusts. For pure dust clouds, as the number of subdivisions and hence d_(50)s increases, variation trend of the MIE as a function of dust concentration (MIE(conc)) gradually shifts from a "V" to a "U" or "bathtub" shape, along with an increase in the concentration where the dust cloud MIE (minimum MIE(conc) value) is reached. Furthermore, the calculated MIE fluctuates at lower number of d_(50)s but gradually stabilizes as the d_(50) number further increases. The calculated MIE variation trends correspond well witii the experimental data. However, due to uncertainties in the dust cloud formation and spark release in the experimental tests, differences in the definitions of the d_(50) in different studies and high idealization of the numerical model, there are deviations between the absolute experimental and calculated MIE values.
查看更多>>摘要：The dynamic mechanisms of self-ignition and flame propagation during high-pressure hydrogen release through a rectangular tube were experimentally investigated using pressure records, flame detection and high-speed photographs. Experimental results show that the minimum burst pressure for self-ignition decreases with an increase in axial distance to the diaphragm and then remains at an almost constant value. The self-ignition onset at the same location of the tube exhibits a certain randomness even if the intensity of the shock wave produced in the tube is similar. Multiple ignitions were observed at the early stage of hydrogen release. They usually had difficulty to sustainably develop and were extinguished owing to oxygen deficiency. At a subsequent stage, the ignition kernel appears again and grows rapidly in the axial and radial directions, finally converging to a complete flame across the tube width. It was found that the radial growth rate of the flame was lower than the axial growth rate.
查看更多>>摘要：The eye-glass polishing wastewater (EGPW) is an increasingly noteworthy problem because of its high chemical oxygen demand (COD), high turbidity and abundant microplastics (MPs), which threatens the aquatic environment as well as human life. In this study, we analyzed the separation performance of MPs from EGPW using sec-octyl alcohol and diesel oil as frother and collector, respectively. The experimental results demonstrated that the removal rate of MPs, COD and turbidity could reach to 93.9 %, 80.4 %, 83.8 %, respectively. The measurement of induction time, Fourier-transform infrared and X-ray photoelectron spectroscopy were measured to explain flotation mechanism of MPs. Sec-octyl alcohol has little effect on the functional groups of MPs and it mainly reduces the surface tension of gas-liquid interface and improves the stability of bubble. Diesel oil increases the C-C/C-H content of MPs, illustrating that it could absorb on the surface of MPs and improve the hydrophobicity of MPs. The induction time decreases with the increasing dosage of both sec-octyl alcohol and diesel oil, thus improving the separation rate of MPs from the EGPW. These results indicate that bubble flotation exhibits great potential to effectively remove MPs and purify the EGPW, anticipating to facilitate the municipal wastewater management.
查看更多>>摘要：Gamma irradiation has received increasing attention due to its high potential in the degradation of recalcitrant pollutants. Thus, in the present study, gamma irradiation was used for the degradation of bromuconazole with the presence of hydrogen peroxide (H2O2) as a source of *OH and humic acid as natural organic matter. The effects of initial concentration, irradiation doses and pH were examined. A kinetic study was performed, and the by-products were identified by HPLC-QTOF-MS/MS. Results showed that the degradation process of bromuconazole was pseudo-first-order and 99.9% of bromuconazole was decomposed under an absorbed dose of 1 kGy. The percentage of removal increased with doses and the degradation process was accelerated under neutral conditions. The addition of H2O2 showed a synergistic effect on the decomposition of bromuconazole and the degradation efficiency increased with the increase of H2O2 concentration. Humic acid indicated a negative influence on the degradation efficiency, which decreased from 99.6% to 70.365% at a dose of 0.8 kGy when the humic acid concentration was 20 mg/L. Six degradation products were identified and the kinetic rates of three intermediate compounds were calculated using a Himmelblau-Jones-Bischoff numerical analysis technique. A study conducted by ~1H NMR indicated a complete mineralization at 1.2 kGy.
查看更多>>摘要：Bisphenol analogues (BPs) have been widely used in industrial production, and caused harmful effects on biological reproduction and development. The occurrence characteristics of six BPs in multi-matrices, including truly dissolved phase, colloids, suspended particulate matter (SPM), sediment and fish samples from urban river were investigated. Bisphenol A (BPA) and bisphenol S (BPS) were the mostly detected in six BPs in the Yangtze River (Nanjing section). The total average concentration of BPs was 393.8 ng/L in truly dissolved phase, 57.4 ng/ L in colloids, 255.2 ng/g in SPM and 34.5 ng/g in sediment. The adsorption capacity of SPM and sediment to BPs were weaker than that of colloids. For the spatial variation, the concentrations of BPs in the surface water of the downstream of urban rivers were 1.3-1.6 times higher than that of the upstream, and the BPs concentrations in the sediments downstream of the sewage treatment plant were significantly higher than that in other sites. In wild fish, muscle has a high accumulative potential for BPs, followed by brain and liver tissues, and BPA was the dominant BPs in brain tissues. Furthermore, BPs concentration in muscle of wild fish with different feeding habits was in the following order: filter-feeding fish > omnivorous fish > herbivorous fish, and which was significantly positively correlated with BPs concentration in traditionally dissolved phase and colloidal phase. Meanwhile, BPs concentration in benthic herbivorous fish might be also controlled by the BPs adsorbed in the sediment. Ecological risk assessment was conducted and demonstrated that BPs might pose a moderate risk to fish, a low risk to algae and daphnias. The detected BPs does not pose a health risk to human trough drinking water and eating fish alone.
查看更多>>摘要：Optimizing the tunnel ventilation scheme is one of the main ways to achieve safe production in coal mines. Based on the actual production situation, computational fluid dynamics technology was used to study the distribution characteristics of an airflow-dust mixture for different air-absorption volumes (Qe) of the ventilation system during sub-regional coal cutting. According to the dust concentration values registered at different locations, the entropy weight method was applied to quantitatively analyze the dust absorption effect of the fan. The research results showed that: the dust distribution was jointly affected by the cutting unit and the completed cutting zone;; moreover, the dust control effect was better in the middle cutting zones than in the others. Under the ventilation system, the overall distribution of dust in the tunnel could be roughly divided into three sections: the dust removal section (I), the dust blocking section (II), and the gentle section (III). The optimal Qe (575 m~3/min) was determined based on the weight of the different zones. Finally, the entropy weight method was applied for determining the ideal mine ventilation system scheme and, hence, improve safety production in coal mines during sub-regional cutting dust production.
查看更多>>摘要：The electrostatic precipitator (ESP) is widely used in the purification of oil mist particles in the industrial workshops. Different from the solid particles, the deposition of oil mist particles in the ESP can reach a steady state and form a saturated oil film on the electrode plate. Based on the deposition experiment data, this paper has established the oil film flow model in ESP coupled with the corona discharge, the gas flow and the oil mist particle deposition model. The characteristics of oil mist particles deposition and the oil film flow were studied. The results show that the oil film is thin in the electrode plate where the current density is high. The oil film is thick at the inlet of ESP and the corresponding collection plate in the middle of the adjacent electrode wires. The peak value appears at the corresponding plate in the middle of the first two electrode wires, which is more man 50 μm. The average oil film thickness is about 9 μm in the current study. As the inlet velocity increases or the applied voltage decreases, the oil film distribution becomes more uniform, and the oil holding capacity of the electrode plate increases.
查看更多>>摘要：In order to achieve considerable generation of free radicals during electro-coagulation (EC) process, EC with air breathing cathode (EC-ABC) was designed to allow for the coexistence of electro-Fenton (EF) and EC functions. This EC-EF-ABC synergetic system allows for both in-situ free radicals and adsorptive flocs generation in an undivided electrolytic cell. The yield of hydroxyl radicals and adsorptive flocs were quantified for accurate mechanism analysis. The control mechanism of the transition from EF to EC function during EC-ABC system was investigated. The air cathode material was studied and optimized to obtain high hydroxyl radical generation. The influences of both dissolved oxygen (DO) and pH condition on hydroxyl radical and flocs generation were studied. Whiles the latter was found to dominate the successive EF and EC functions, and further controls the hydroxyl radicals and flocs yield, the former only has a dominant effect on the hydroxyl radical yield. The adsorptive iron (oxy)hydroxide flocs' structure was also found to be fully depend on the DO condition. The control mechanism of initial pH and DO condition on radical and flocs generation was simplified as a 'Sudoku-like' relationship. The optimized initial pH and DO condition was studied to maximize the generation of hydroxyl radicals and adsorptive flocs. The design of EC-ABC process could have both advanced oxidation and adsorption abilities for wastewater pollutant removal.
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