查看更多>>摘要：Volt-Amp profiles are used to describe electrodialysis (ED) dynamics when the concentration of the diluate is equal to the concentration of the concentrate and both are at high concentration. A standard electronic model that treats the ED process as a series of resistors failed to describe the performance of a 10-cell pair, 200 cm(2) per membrane pilot electrodialysis unit treating 0.5-6% NaCl. The standard electronic model resulted in a regression coefficient of R-2 < 0.76 and underestimated the observed system resistance by 0.54 to 1.1 Ohms depending on the conductivity of the test water. However, if the overall process was treated as a saturated chemical reaction, such as a modified Michaelis-Menten function, the regression exceeded R-2 > 0.999. The current was plotted as a function of the conductivity of the salt at a constant conductivity of electrode rinse solution. Each curve was a function of the applied voltage. The value of the saturation coefficient for the system plots as {D-sat} similar to 22.1 mS/cm (2.21 S/m). The kinetic coefficient i mAx plotted as a linear function of the effective voltage at 25 degrees C (298 degrees K). More importantly, a series of tests with a constant feed conductivity and with varied electrode rinse solution conductivity also plotted as Michaelis-Menten type curves. The saturation coefficient for the electrode rinse solution also fitted well to {E-sat} similar to 22.1 mS/cm (2.21 S/m) and the values for i( MAX) were also linear with respect to applied voltage. Overall, the results from 12 data sets follow the formula i = alpha beta i( MAX) where alpha and beta are the ratios of the conductivity of the fluid divided by the sum of the conductivity plus the saturation, e.g., for electrode rinse solution alpha = {E}/({E} + {E-sat}) and for the electrode rinse beta = {D}/({D} + (D-sat}), indicating the co-dependence of the feedstock and electrode rinse in the overall process dynamics. This interpretation is in opposition to the standard modeling of ED where the process is viewed as a series of resistances and the electrode rinse resistance is usually determined to be negligible. These data suggest that the effects of saturated feedstock and saturated rinse solution, measured as current or ion transport, are inextricably co-dependent. Three full-batch test runs of between 7.2 and 9-hr duration using different initial feedstock and electrode rinse water conditions were analyzed to estimate the relative effects of diluate and concentrate concentration on the test results. A third saturation coefficient was introduced, gamma = {C}/({C} + {C-sat}) where the terms {C} and {C-sat} represent the conductivity and the saturation coefficient of the concentrate. The model for long duration batch tests, including the different effects of the concentrate and diluate, is well represented by i = (alpha beta(0.)(8) gamma (0.2) i (MAX)). The empirical power coefficients, beta(0.)(8)and gamma(0.2), indicate that the diluate conductivity carries more influence on the rate of the process than does the conductivity of the concentrate. The model has the potential to allow for the scale-up of the ED process using at most one adjustable parameter (the saturation coefficient of the membrane measured as mS/cm or S/cm). Michaelis-Menten kinetics and the modifications by others represent a rich literature on the modeling of different types of inhibition, topics of concern for membrane transport phenomenon.
查看更多>>摘要：This study gathers the results of the operation and optimization of the thickening of microalgal biomass produced at demonstrative scale in photobioreactors fed with agricultural runoff and domestic wastewater. The optimization was conducted during two months. The system consisted in two gravity thickeners connected in series in a multi-stage approach. The objective of thickening was to concentrate the microalgae grown in photobioreactors (total solids (TS) concentration of 0.1-1 g/L) into a biomass with 20 g/L of TS, which was considered optimal for the subsequent anaerobic digestion process. First, the utilization of one single thickener alone allowed to achieve a concentration factor (CF) of 1.9 and recovery efficiency (RE) of 28%. However, the final concentration of TS in the thickened biomass (6.4 g/L) was still much lower than the target concentration. The installation of the second thickener connected in series with the first one significantly improved the overall performance. Indeed, a TS concentration of 26.5 g/L was finally achieved, with an overall CF of 3.6. The results of the study suggest that the multi-stage thickening process is a suitable strategy and it is highly advisable to achieve a successful microalgal biomass thickening at full-scale. In addition, other three points have been identified as key factors to be taken into account for biomass tickening: proper adjustment of the purge flowrate, coordination between purges times and volumes in the different stages, and proper adjustment of the operation of the scrapers.
查看更多>>摘要：This work presents a novel electro-electrodialysis (EED) system for laboratory-scale uranium electrowinning based on a simple process of reactive electmdialysis of solutions of uranium (VI) oxide (UO3) dissolved in aqueous hydrofluoric acid (HF), leading to the formation of deposits of uranium tetrafluoride (UF4). For stainless steel cathodes, the best operating conditions for a concentration of 25 g/L for uranium were i = 40 A/m(2), T = 40 degrees C and 18 L/h electrolyte recirculation flowrate. The specific energy consumption (W) and current efficiency (p) for tetra uranium fluoride electrowinning was 4500 kWh/kg and 10.15%. When the cathodic metal was changed from stainless steel to aluminium, seeking to optimize the system, improved values of W and rho were achieved (645 kWh/kg and 68%, respectively). In the EED cells, the release of gaseous hydrogen is significantly lower for aluminum, due to its lower exchange current density (i(0)), with a magnitude of 10(-7) A/m(2). On the contrary, a considerable release of gaseous hydrogen is observed when the stainless-steel cathode is used, mainly due to the H+/H-2 reaction being catalysed by the stainless steel, inducing an increase in the acid consumption rate, devoting most of the energy consumed by the system in the proton reduction reaction. Polarization cathodic curves indicate that uranium has an estimate resting potential close to that of aluminium, which is -0.89 V. Finally, by chemical analysis (X-ray mass diffraction), UF4 and hydrated UF4 were identified as the main components of the electrodeposited product.
查看更多>>摘要：Because of the stability of its production and cost-effectiveness, coal is expected to be a primary energy source in near future. However, SO2 and NOx emissions from the coal combustion have been considered a serious environmental issue in the last few decades; they react with water vapor and ammonia (NH3) in the atmosphere to form secondary aerosols. In this study, ozone (O-3) was injected to oxidize NO into NO2. Thereafter, NH3 was injected to convert SO2 into (NH4)(2)SO3 particles, which further reacted with NO2 to produce N-2 and (NH4)(2)SO4 particles. These reaction mechanisms were discussed employing different chemical analyses of the products. Moreover, the size of the product particles was analyzed by online particle size analysis and the scanning electron microscopy images. Further, the quantitative analysis of the product was performed by ion chromatography, and the atomic balance of sulfur was verified by gas analysis. A higher SO2 concentration increased the NOx removal efficiency because the product ((NH4)(2)SO3), which was obtained from SO2 removal, acted as a reactant for the removal of NOx. Therefore, a higher concentration of O-3 favored the improvement of the NOx removal efficiency since O-3 oxidizes NO into NO2, which reacts with (NH4)(2)SO3. Thus, the SO2 and NOx removal efficiencies were 93.6% and 69.6%, respectively, at SO2, NO, and O-3 concentrations of 900, 30, and 30 ppm, respectively.
Mbaye, MoussaDiaw, Pape AbdoulayeMbaye, Olivier Maurice AlyOturan, Nihal...
9页
查看更多>>摘要：The electro-Fenton (EF) process was used to assess the electrochemical degradation of the fungicide thiram and its complete removal from water using an undivided electrolytic cell equipped with Pt or BDD anode and carbon felt cathode. Hydroxyl radicals, produced homogeneously in bulk solution from electrochemically generated Fenton's reagent (center dot OH) and heterogeneously on the anode surface (MCOH)) from oxidation of water, reacted with thiram leading to its fast oxidation. Oxidative degradation and mineralization kinetics were monitored by chromatographic analysis (HPLC) and total organic carbon (TOC) measurements. The electrochemical degradation of thiram by hydroxyl radicals followed a pseudo-first-order reaction kinetics with an absolute rate constant k(abs(Thir)) of 5.54 (+0.03) x 10(9) M s(-1), determined by competition kinetics method. The TOC removal rate values were found significantly higher with BDD anode than Pt anode. Thus, almost complete mineralization (92%) of thiram solution was obtained when using BDD anode. These results highlight the major role of heterogeneous BDD(center dot OH) formed in the mineralization of thiram. The contribution of homogeneous center dot OH in mineralization of thiram was found relatively low due to its specific aliphatic structure. The efficiency of the EF process was evaluated by determining mineralization current efficiency and energy consumption per gram of TOC removed. Degradation by-products and inorganic ions, such as nitrate (NO3-), nitrite (NO2-), ammonium (NH4+) and sulfate (SO42-) formed during mineralization process, were identified by GC-MS and ionic chromatography analyses and a plausible mineralization pathway was proposed.
查看更多>>摘要：Sulfanilic acid (SA) is an important organic compound with numerous applications in industrial production, while the organic wastewater with high salinity is inevitably generated. In this work, desalination strategy of hypersaline SA wastewater was proposed by using bipolar membrane electrodialysis (BMED), which can realize the separation of SA and NaCl in wastewater and the conversion of NaCl into HCl and NaOH simultaneously. The influences of current density, initial concentrations of acid, base, SA and salt were investigated. The results showed that current efficiency decreased and energy consumption increased with an increase in current density. Higher initial concentrations of acid and base were favor to reduce energy consumption but current efficiency was low. At the current density of 40 mA/cm(2), the initial acid and base concentrations of 0.10 mol/L, the highest concentrations of HCl and NaOH with initial salt concentration in the simulated feed solution of 80 g/L NaCl was 1.17 mol/L and 1.18 mol/L, respectively. Moreover, the total process cost of BMED process was estimated at $1.68/kg HCl and $1.52/kg NaOH respectively under the optimal experimental conditions. These findings confirmed that BMED may be an alternative and cost-effective strategy for treating high salinity SA wastewater.
查看更多>>摘要：An amidoxime modified carbon cloth electrode (CC-AO) was applied for uranium electrosorption at low pH value of 2. Experiments using other carbon-based electrodes were also carried out for comparison. The kinetics, isotherm, selectivity, reusability and power consumption during the uranyl ions (UO22+) electrosorption were studied in-depth. The effects of voltage and frequency on UO22+ selectivity among coexisting ions were investigated. The results showed that UO22+ (20 mg/L), removal by CC-AO was 94.3% at pH = 2 with a high electrosorption capacity of 989.5 mg/g (within 12.5 h). The electric field drove UO22+ to move to the cathode surface and produced UO3.2H(2)O on CC-AO. Under the optimal electric field (- 2.5 V, 800 Hz), CC-AO achieved the highest UO22+ selectivity in the simulated acidic uranium mine wastewater, and the frequency was the main factor. The CC-AO can be effectively used for seven UO22+ electrosorption-desorption cycles. Moreover, a new index of "unit power consumption for half amount uptake" (PC1/2) was proposed to quantify the power consumption during UO22+ uptake by different electrodes. In electrosorption system, the available area of CC-AO is larger than that of CF-AO, so its electrosorption efficiency for UO22+ is much higher than the latter. The current CC-AO showed clear advantages in terms of electrochemical features, adsorption capacity, selectivity, and power consumption at such low pH condition, indicating an application potential for uranium recovery from acidic uranium mine wastewaters.
查看更多>>摘要：Nitrogen-doped carbon materials can effectively activate peroxymonosulfate (PMS) to degrade organic pollutants. In this study, one or more of the following raw ingredients, ferric nitrate, dopamine hydrochloride and melamine, were used as raw materials to prepare different carbon-based catalysts. The different effects of each raw ingredient on the performance of the catalyst were studied. Characterization by X-ray diffract grams spectra, Raman spectroscopy and X-ray photoelectron spectroscopy found that Fe(NO3)(3)center dot 9H(2)O in the catalyst is beneficial to promote the degree of graphitization, and melamine can increase the nitrogen content in the catalyst. The prepared Fe-DA-CN catalyst, prepared with three materials has the highest activity. When the catalyst dose was 50 mg/L and the PMS concentration was 0.25 mM, the removal rate of 5 mg/L sulfamethoxazole (SMX) reached more than 99% after 30 mM of reaction; furthermore, the pH, presence of inorganic anions (HPO42-, NO3, CO32-, Cl-) and presence of humic acid had little effect on the SMX removal rate. Repeated use experiments show that the catalyst has good stability. Through electron paramagnetic resonance and quenching tests, it is found that the main active substances that activate PMS to degrade SMX are free radicals (center dot OH, SO4-) bound on the catalyst surface and a small part of singlet oxygen (O-1(2)).
查看更多>>摘要：Through the purification technology of flue gas desulfurization, ultralow emissions of SO2 flue gas in industrial flue gas can be achieved. This article involves dry desulfurization, semi-dry desulfurization, and wet desulfurization technologies. The research progress of these technologies since they were first proposed is summarized, and the problems existing in these desulfurization technologies are analyzed. The theory of mass transfer and absorption in flue gas desulfurization is summarized, and the optimal desulfurization process parameters for the operation of desulfurization technology are obtained. A high added value production of desulfurization technology can be realized by studying the recycling of desulfurization products. This paper summarizes the characteristics and the latest research progress of various desulfurization technologies, and aims to provide help for the better development of desulfurization technologies. It also provides suggestions for the future research direction of desulfurization technology.
查看更多>>摘要：As one of the high-efficiency triazole fungicides, diniconazole (DIN) has been used on a large scale in agricultural production. Due to its high stability and toxicity, DIN is usually persisted in soil and water and has been demonstrated to be a potential threat to environment and humans. In this study, the degradation kinetics, mechanisms, and degradation products of DIN by peroxymonosulfate (PMS) activated with alpha-MnO2 were systematically studied. The results showed that DIN was rapidly degraded in alpha-MnO2 activated PMS system, and the degradation kinetics of DIN in this reaction system could be described by the pseudo-first-order kinetic model. The degradation of DIN was affected by environmental conditions. Acidic condition was beneficial to the degradation of DIN, whereas co-existing anions (HPO42-, Cl- and HCO3-) and humic acid inhibited the degradation of DIN in MnO2 activated PMS system. SO4 center dot- and HO center dot generating from PMS activated by alpha-MnO2 were confirmed as the major active species in degradation of DIN. The potential sites attacked in the DIN structure might be 11Cl, 10Cl, 14C and 17C based on the DFT calculation. Moreover, the degradation pathways of DIN were proposed, including hydroxylation, hydroxyl addition, cleavage of 14C-15N and intramolecular cyclization.
NSTL
Elsevier