Bi2MoO6/AgBr的制备及其光催化活性增强机制

采用水热法合成了Z型异质结Bi₂MoO₆/Ag Br光催化剂,利用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、比表面积测试仪(BET)、稳态/瞬态荧光光谱仪等对其微观形貌、物相组成以及光电性能等特性进行表征;通过对目标污染物罗丹明B(Rh B)的降解分析该催化剂的活性和降解机理。结果表明,该催化剂由立方相的Bi₂Mo O₆纳米片堆叠而成的纳米微球和负载在其表面的Ag Br纳米花簇构成,异质结的形成使得比表面积增加了7.2 m²/g,光生电子对寿命延长。Bi₂Mo O₆与Ag Br复合后光催化活性明显提高,当Ag Br复合量为10%时效果最佳,光催化反应速率常数是Bi₂Mo O₆的1.6倍。当Rh B浓度为0.5×10^-5mol/L、Bi₂Mo O₆/Ag Br投加量为250 mg/L、p H值=7时,反应20 min后对Rh B的降解率可达到95.9%,且Bi₂Mo O₆/Ag Br经过5次循环实验后仍具有较高的光催化活性。自由基捕获实验结果表明,Bi₂MoO₆的主要活性基为·O₂^-,Bi₂Mo O₆/Ag Br的主要活性基团为·O₂^-和h⁺。根据以上实验结果,提出了一种由Ag⁰粒子为通道的Z型电荷转移机理。     

Effect of different catalysts in SO2 oxidation over polymeric concrete

Polymeric concrete performance in polluted environment has been studied in order to determine outdoor pollutant transfer process. SO₂ oxidation process over different building materials in laboratory-based atmospheric flow chambers is well known; however, the effect of NO_x is not very clear. In order to clarify this process, the effect of NO_x in SO₂ oxidation over the surface of a porcelain material was studied under wetted and unwetted conditions. In the chamber, NO_x can either catalyse SO₂ reaction or undergo oxidation to NO₃⁻. The main conclusion in this work is that for the porcelain samples under wetted conditions NO and NO₂ catalysed the reaction. But in unwetted conditions NO reacts with the sample instead of SO₂.     

Studies on marine biological filters: Model filters

Model systems of 401. capacity were used to study chemical changes which affected buffering in continuously recycled sea water and which restricted nitrification in percolating biological filters at 28°C.

Sustained hydrogen ion production during the microbial oxidation of ammonia to nitrite caused continuous carbon dioxide formation from carbonate and bicarbonate. The carbon dioxide was steadily lost to the air through vigorous aeration, leaving < 2 mg inorganic carbon 1⁻¹ in the sea water. Oxidation of nitrate to nitrate did not significantly reduce pH nor deplete buffer capacity.

Ammonia oxidation was severely inhibited by the combination of low pH and dissolved inorganic carbon levels, but similar low levels of pH produced when carbon dioxide was bubbled through the water had only a moderate effect. Inhibition could be rapidly overcome or prevented by additions of inorganic carbon, sodium hydroxide or sodium dihydrogen phosphate.

Values recorded for the maximum specific growth rate of Nitrosomonas and Nitrobacter were 0.53 and 0.81 d⁻¹ respectively. The corresponding generation or doubling times were calculated to be 31.4 and 20.5 h.

Some evidence was found for the uptake of phosphate and the formation of hydroxylamine during nitrification.     

Utilisation de l''algue oocystis sp. pour le traitement tertiaire des eaux usées—I. Culture en vrac de cellules préalablement conditionnées en cyclostat

With the aim of developing an efficient and economic method for the tertiary treatment of wastewater, a two-phased culture system of Oocystis alga is presented. During the first phase, a unialgal strain grows in a cyclostat supplied with secondary effluents diluted to a low concentration (50 μM NH₄⁺, i.e. 0.7 mg N 1⁻¹) of inorganic ions. Once the equilibrium is reached (i.e. the cell population is conditioned and the nutrient concentration is zero), in a second phase, the starved cells are mixed with a secondary effluent which has a higher nutrient content (200–400 μM NH₄⁺, i.e., 2.8–5.6 mg N 1⁻¹). Ion depletion (NH₄⁺, NO₃^-, NO₂^- and PO₄^3-) follows specific kinetics; successive identifiable stages related to photoperiod lead to a complete stripping of nutrients. In addition to ion concentrations, pH and cell population were determined every 2 h during the experiment. Results and conclusions are presented.     

A comparison of fenuron degradation by hydroxyl and carbonate radicals in aqueous solution

A comparative study of the transformation of the herbicide fenuron (1,1-dimethyl-3-phenylurea) by hydroxyl radicals and carbonate radicals in aqueous solution (pH 7.2-phosphate buffer) has been undertaken. Hydroxyl radical was generated by the well-known photolysis of hydrogen peroxide at 254 nm and carbonate radical was formed by photolysis of Co(NH₃)₅CO₃⁺ at 254 nm. Competitive kinetic experiments were performed with atrazine used as the main competitor for both processes. Accordingly, the second-order rate constant of reaction between fenuron and carbonate radical was found to be (7−12±3)×10⁶ M⁻¹ s⁻¹ [(7±1)×10⁹ M⁻¹ s⁻¹ for hydroxyl radical]. The formation of degradation products was studied by LC-MS in the two cases and a comparison has been performed. The reaction with carbonate radical leads to the formation of a quinone-imine derivative which appears as the major primary product together with ortho and para hydroxylated compounds. These two compounds represent the major products in the reaction with hydroxyl radicals. The reaction of both radicals also leads to the transformation of the dimethylurea moiety.     

The effect of different drinking water treatment processes on the rate of chloroform formation in the reactions of natural organic matter with hypochlorite

This study is concerned with the changes in the rate of chloroform formation during the reactions of groundwater natural organic matter (NOM) and sodium hypochlorite caused by different drinking water treatments schemes: coagulation with FeCl₃, Al₂(SO₄)₃ and polyaluminum chloride (PACl), filtration of the raw water through granular activated carbon (GAC) and filtration through the columns filled with strong base macroporous ion-exchange resins (Purolite A501P and A500P) with and without pretreatment by coagulation process. It was found that the change of the concentration of chloroform, within 2 h and c(Cl₂)=100 mg l⁻¹, can be described by a kinetic equation of the form [CHCl₃]=a+bt^c. On the basis of this equation rates of the reaction were calculated. All processes applied decreased the rate of chloroform formation (process of coagulation moderately decreased the rate of reactions, while GAC adsorption caused dramatically drop of the rate). Also, it was found that the resins have had a higher affinity towards slow-reacting chloroform precursors.

The value of the chloroform formation potential was conventionally determined after a 7-day reaction at pH 7. In addition, the same parameter was estimated with a satisfactory deviation for raw water and for treated water on the basis of the kinetic constant (k) or by determining the chloroform concentration after 2 h (ChFP₂) under rigourous chlorination conditions at pH 8.4.     

Accumulation of nitrous oxide in aerobic groundwaters

N₂O concentrations in the groundwaters collected in the Kanto District and Nagano Prefecture in Japan and five counties in New York State were determined. These N₂O data were obtained from the water samples from wells, springs and seepages from soils in forests and cropping fields. The N₂O concentrations in all samples greatly exceeded those of atmospheric equilibration. The average concentration of 690 nM N₂O is one order of magnitude larger than that in deep ocean. All groundwaters of the present study were aerobic with a high level of NO₃⁻, but with the absence of NO₂⁻ and NH₄⁺, and with a very low level of dissolved organic carbon. These characteristics suggest that the nitrate respiration in the aquifers is of little significance for the production of N₂O.

ΔN₂O/NO₃⁻ molar ratios in the groundwaters were between 10⁻⁴ and 10⁻² (Δ indicates the excess gas over that which would be in equilibrium). This supports the above view since the observed N₂O yield agrees with that reported for the production during an ammonia oxidation. If nitrification was indeed a major mechanism for the production of groundwater N₂O, subsequent release of N₂O from the aquifers that are polluted with nitrogen may deserve more close attention as a potential source of atmospheric N₂O via diffusion and discharge.     

惰性介质对铝粉抑爆效果的试验研究

基于siwek-20 L爆炸测试系统,在试验分析碳酸钙、碳酸氢钠和磷酸二氢铵这3种惰性介质的惰化性能的基础上,进一步研究其介质之间的协同增效效应。结果表明：对于浓度为300 g/m³的铝粉,惰性介质能使铝粉爆炸受到明显的抑制,且随着惰性介质含量的增加,铝粉爆炸强度不断下降;NH₄H₂PO₄的抑制效果优于CaCO₃,CaCO₃优于NaHCO₃;添加CaCO₃与NH₄H₂PO₄配比的复合惰性介质和NaHCO₃与NH₄H₂PO₄配比的复合惰性介质时,铝粉爆炸受到进一步的抑制,体现出惰性介质之间的协同增效效应,其中CaCO₃与NH₄H₂PO₄按照1∶1配比的复合惰性介质抑爆性能最佳。     

Catalytic wet oxidation of phenol over a Pt/TiO catalyst

Wet oxidation of phenol by air or oxygen over a Pt/TiO₂ catalyst is studied in a batch reactor in the temperature range 150–200°C, pressure range 34–82 atm, and a catalyst loading range of 0–4 g catalyst L⁻¹. The catalyst was powdered 4.45% Pt/TiO₂ with a maximum particle size of 105 μm. Results show complete oxidation of phenol and almost complete total organic carbon (TOC) removal. Small amounts of stable organic acids are formed in side reactions of the phenol degradation pathway and are not readily degraded. Experimental results show that the reaction rate decreases by increased oxygen concentration. Theoretical rate expressions are derived, based on postulated oxidation and TOC reduction mechanisms.     

生物炭混凝土生命周期CO2排放评价

为评价生物炭混凝土的CO₂排放量,采用生命周期评价技术构建了生物质热解生产生物炭过程的碳排放计算模型、生物炭混凝土从原材料生产到混凝土拆除废弃阶段CO₂排放量化模型和生物炭混凝土服役期碳化-吸收模型,同时研究了生物炭按质量比例取代水泥对混凝土力学性能的影响。在此基础上,计算了1 m³C30生物炭混凝土的CO₂排放量,并与普通C30混凝土CO₂排放量进行对比。结果表明:生物炭作为一种碳负性材料,其碳元素含量越高,CO₂减排效果越好; 当生物炭取代率小于5.0%时,研磨后的超细炭颗粒可以充分发挥填充和内固化效应,有效地提高混凝土的力学性能; 生物炭混凝土生命周期CO₂排放量随生物炭取代率的提高而降低,5%取代率的1 m³木屑生物炭混凝土相比普通C30混凝土,可减排CO₂66.5 kg,减排率为20.7%; 生物炭混凝土在服役期内因碳化吸收CO₂占总碳排放量的1.8%～2.5%,而拆除废弃阶段由于混凝土的比表面积呈指数增长,碳化吸收量需要进一步研究。     

A contribution to environmental risk assessment for transport of cadmium through groundwater layers. Case study of the Sava river (near Zagreb, Croatia) region

Adsorption capacities of cadmium on aquifer material of the Sava River alluvial sediment were determined as a function of flow rate, pH and presence of organic coating using laboratory column technique. In a permeameter with constant hydrostatic pressure, a laboratory coefficient of permeability, K_l, and a specific coefficient of permeability, K_s, have been determined. The value of 28.6 Darcy for specific permeability shows that the sediment belongs to a good aquifer (permeability >1 Darcy). The adsorption capacity of cadmium at the bottom of the breakthrough curve, C_sb, of a fresh sediment at pH 5.8 varied from 0.40 to 0.45 mg g⁻¹ at axial flow rate between 98 and 501 cm h⁻¹. Capacity values of maximum adsorption, C_s, were in the range from 0.67 to 0.72 mg g⁻¹. This implies a significance of C_sb values in risk assessment studies concerning a discharge of cadmium into rivers and lakes and its input to groundwater layers. Distribution coefficients, K_d, were between 26.3 and 28.2 ml g⁻¹. In order to create a more reproducible column, a fraction between 125 and 250 μm was used. In that case C_s values varied from 0.25 mg g⁻¹ at pH 2.5 (organic coating present) to 1.12 mg g⁻¹ at pH 5.8 (organic coating removed).     

Modes of operation and pH control as enhancement factors for partial nitrification with oxygen transport limitation

Sequencing batch (SBR) and continuous operation modes were applied using different pH control strategies to enhance partial nitrification in a biofilm rotating disk reactor. The pH control strategies were supervisory control in the range of 7.5–8.6 and fixed pH at 7.5 and 8.5, at dissolved oxygen (DO) concentrations in the range of 0.6–5.0 mg O₂/L. Supervisory pH control enabled operation at a free ammonia concentration inhibitory to the nitrite-oxidizing bacteria (NOB) and an optimum for the ammonia-oxidizing bacteria (AOB). The results indicate that both operation modes were simultaneously controlled by oxygen transport and micro-kinetics (influenced by pH and NH₃). The SBR mode with supervisory pH control presented more stable partial nitrification-nitrite accumulation >80% for 249 days than continuous operation. Molecular analyses showed that the SBR operation with supervisory pH control at low DO concentrations contributed to the enrichment of the AOB (>95%) over the NOB (<5%) populations. Therefore, it can be stated that a suitable pH control strategy can act as an enhancement factor of partial nitrification even under oxygen-transport-limiting conditions.     

Prediction on CO2 uptake of recycled aggregate concrete

Carbonation of concrete is a process which absorbs carbon dioxide (CO₂). Recycled aggregate concrete (RAC) may own greater potential in CO₂ uptake due to the faster carbonation rate than natural aggregate concrete (NAC). A quantitative model was employed to predict the CO₂ uptake of RAC in this study. The carbonation of RAC and the specific surface area of recycled coarse aggregates (RCAs) were tested to verify accuracy of the quantitative model. Based on the verified model, results show that the CO₂ uptake capacity increases with the increase of RCA replacement percentage. The CO₂ uptake amount of 1 m³ C30 RAC within 50 years is 10.6, 13.8, 17.2, and 22.4 kg when the RCA replacement percentage is 30%, 50%, 70%, and 100%, respectively. The CO₂ uptake by RCAs is remarkable and reaches 35.8%–64.3% of the total CO₂ uptake by RAC when the RCA storage time being 30 days. Considering the fact that the amount of old hardened cement paste in RCAs is limited, there is an upper limit for the CO₂ uptake of RCAs.     

Optimizing experimental design to estimate ammonia and nitrite oxidation biokinetic parameters from batch respirograms

Knowledge of relative NH₄⁺–N to NO₂⁻–N oxidation and NO₂⁻–N to NO₃⁻–N oxidation dynamics is essential before application of either single-step or two-step nitrification models to fit batch nitrification respirograms. We have previously shown that two step nitrification models based on respirometry permit the estimation of kinetic parameters for both nitrification steps from a single respirogram associated with NH₄⁺–N to NO₃⁻–N oxidation. However, two-step model parameter estimates are meaningful only under circumstances when the respirograms contain sufficient kinetic information pertaining to both steps. In this study, we present an operationally amenable extant batch nitrification respirometric assay to engender maximal information content in the resulting respirograms with respect to both constituent nitrification steps. The developed design consists of an initial NH₄⁺–N pulse to a nitrifying biomass sample followed by an additional NO₂⁻–N pulse at an optimal time point, which can be rigorously determined by maximizing the value of the determinant of the Fisher information matrix, Det(F) or, alternatively, by visually identifying the point of NH₄⁺–N depletion during the respirometric assay. The proposed design is applicable for accurate determination of the Monod kinetic parameter estimates for both nitrification steps from batch respirograms even when the pseudo-first order rate coefficients for the two nitrification steps are nearly equal; a condition under which standard NH₄⁺–N to NO₃⁻–N respirograms typically lack information with respect to NO₂⁻–N oxidation.     

Characterization of nitrifying granules produced in an aerobic upflow fluidized bed reactor

Since nitrification is the rate-determining step in the biological nitrogen removal from wastewater, many research studies have been conducted on the immobilization of nitrifying bacteria. In this research, granulation of nitrifying bacteria in an aerobic upflow fluidized bed (AUFB) reactor in a nitrification process for inorganic wastewater containing 500 g/m³ of NH₄⁺-N was investigated. It was observed that spherical, pseudocubic and elliptical granules with a diameter of 346 μm were produced at the bottom of the reactor after 300 days. Denaturing gradient gel electrophoresis analysis revealed that Nitrosomonas-like bacteria were the dominant ammonia-oxidizing species in the granules. Many colonies of Nitrosomonas-like bacteria were found in the outer part of the granules based on the spatial distribution analysis by fluorescence in situ hybridization. By stepwise reduction of the hydraulic retention time, the ammonia removal rate of the AUFB reactor containing these nitrifying granules finally reached 1.5 kg-N/m³/day. Results suggested that the use of granules realizes the retention of a large amount of nitrifying bacteria in the reactor, which guarantees a highly efficient nitrification.     

Etude de l'oxydation de chloroethanes en milieu aqueux dilue par H2O2/u.v.Degradation of chloroethanes in dilute aqueous solution by H2O2/u.v.

The destruction of organic pollutants in water can be achieved by the combination of oxidants or of oxidants with u.v. radiation (O₃/H₂O₂;; H₂O₂/u.v.; O₃/u.v.). The efficiency of these advanced oxidation processes is accounted for by the generation of very reactive free radicals such as hydroxyl radicals. In this paper, experimental data are presented to examine the effect of physico-chemical parameters on the efficiency of the H₂O₂/u.v. process for the degradation of chloroethanes in dilute aqueous solution and to test a kinetic model for this oxidation process. The model is based on known reactions of OH radicals in water and on kinetic results obtained in a previous work for the photodecomposition of hydrogen peroxide (Nicole et al., 1990).     

Studies on the persistence of some carbamate insecticides in the aquatic environment—I. Hydrolysis of sevin, baygon, pyrolan and dimetilan in waters

This paper describes the analysis and rates of hydrolysis of the monoalkyl carbamate insecticides Sevin and Baygon, and the dialkyl carbamates Pyrolan and Dimetilan in aqueous media. The rates of hydrolysis with different hydroxylion concentrations were measured. Second order rate constants for Sevin, Baygon, Pyrolan and Dimetilan at 20°C were found to be 2.04 x 10², 3.04 x 10, 7.0 x 10⁻¹ and 3.4 x 10⁻³ 1. mol⁻¹ min⁻¹, respectively, indicating that the dialkyl carbamates were more stable to alkaline hydrolysis than the monoalkyl carbamates. The rates of hydrolysis at different pH values, ranging from 4.0 to 10.0, were also studied. All the compounds were stable to hydrolysis within the acidic pH range. However, measurable hydrolysis was observed at pH 7.0 and 8.0 for sevin and baygon, respectively, and the rates of hydrolysis increased with the rise of the pH value. At pH 8.0 about 99 per cent of sevin was hydrolyzed in 9 days while baygon reached the same level of hydrolysis after 107 days. Pyrolan and Dimetilan, on the other hand, were stable towards hydrolysis within the investigated pH range. The effect of temperature on the rates of hydrolysis was also investigated. This study shows that the persistence of the carbamate pesticides in natural waters is greatly influenced by the pH value and temperature of the aquatic environment.     

Empirical rate equation for trihalomethane formation with chlorination of humic substances in water

Trihalomethane (THM) in drinking water is formed by chlorination of humic substances. In this study, the rates of THM formation in aqueous solution of humic acid were examined under various conditions. The following rate equation was obtained empirically. [THM] = k (pH − a)[TOC][Cl₂]₀^mtⁿ.

Here, [THM] is the concentration of total THM after t h, [TOC] and [Cl₂]₀ are the concentrations of total organic carbon and chlorine dose, k is the rate constant and a, m and n are parameters. The values of k, a, m and n for humic acid as reagent were obtained as 8.2 × 10⁻⁴ (l^mmg^−mh⁻ⁿ), 2.8, 0.25 and 0.36, respectively. The activation energy was obtained as 37 kJ mol⁻¹. Further, it was proved that the above equation could be applied to the rates of THM formation from precursors in actual river and lake waters.     

Electrochemical Treatment of Acidic Aqueous Ferrous Sulfate and Copper Sulfate as Models for Acid Mine Drainage

Acid mine drainage (AMD) is a serious environmental problem in the mining industry. The present work describes electrolytic reduction of solutions of synthetic AMD, comprising FeSO₄/H₂SO₄ and CuSO₄/H₂SO₄, in flow-through cells whose anode and cathode compartments were separated using ion exchange membranes. In the case of FeSO₄/H₂SO₄ at constant flow rate, the pH of the effluent from the catholyte increased progressively with current at a variety of cathodes, due to electrolytic reduction of H⁺ ions to elemental hydrogen. Near-quantitative removal of iron was achieved by sparging air into the catholyte effluent, thereby precipitating iron outside the electrochemical cell, and avoiding fouling of the electrodes. The anode reaction was the oxidation of water to O₂, a proton-releasing process. Using cation exchange membranes and sodium sulfate as the supporting electrolyte in the anode compartment, the efficiency of the process was compromised at high currents by transport of H⁺ competitively with Na⁺ from the anode to the cathode compartments. Higher efficiencies were obtained when anion exchange membranes were used, and in this case no additional supporting electrolyte other than dilute H₂SO₄ was needed, the net reaction being the electrochemically driven transfer of the elements of H₂SO₄ from the cathode to the anode compartments. Current efficiencies 50% were achieved, the loss of efficiency being accounted for by ohmic heating of the solutions. In the case of CuSO₄/H₂SO₄ and anion exchange membranes at high currents, reduction of Cu²⁺ and H⁺ ions and transport of SO₄²⁻ ions out of the catholyte caused unacceptably high potentials to be generated.     

Photodecomposition du bioxyde de chlore et des ions chlorite par irradiation U.V. en milieu aqueux—partie I. Sous-produits de reactionPhotodecomposition of chlorine dioxide and chlorite by U.V.-Irradiation—Part I. Photo-products

Literature data about the photochemistry of oxychlorine compounds in aqueous solutions (flash photolysis, pulse radiolysis, solar radiation) indicate that the products (ClO, Cl, O, O⁻,…) generated from the primary photochemical reactions of decomposition of chlorine dioxide and hypochlorite can then initiate complex reactions which lead to the formation of many secondary products (Cl₂O₂, Cl₂O₁, ClO⁻,…) and of chlorate, chloride and molecular oxygen as end-products (Table 1). The aim of this work was to study the photodecomposition of aqueous solutions of chlorine dioxide and chlorite in u.v. reactors equipped with low pressure mercury vapour lamps in order to show the effects of pH and of the initial concentrations on the nature of photoproducts and on the rate of photodecomposition of ClO₂ and ClO₂⁻. This paper presents the data obtained for the identification of photoproducts. The kinetics of photodecomposition will be presented in another paper (Part II).