Degradation of parathion and the reduction of acute toxicity in TiO2 photocatalysis.

Photocatalytic degradation of methyl parathion was done using a circulating TiO2/UV and TiO2/solar reactor. Indoor experimental results showed that, under the photocatalysis conditions, parathion was more effectively degraded than under the photolysis and TiO2 only conditions. Parathion (38 microM) was completely degraded under photocatalysis within 90 min, and more than 80% TOC decrease after 150 minutes. The main ionic byproducts during the photocatalysis were measured, and almost complete nitrogen recovery was achieved as mainly NO3- NO2-, and NH4+, and 80% of sulfur as recovered as SO4(2)-. Organic intermediates such as nitrophenol and methyl paraoxon were also identified during the photocatalysis of parathion, and these were further degraded after 90 minutes. Microtox bioassay using Vibrio fischeri was used in evaluating the toxicity of solutions treated by photocatalysis and photolysis of parathion. The results showed that the acute toxicity expressed as EC50 almost reduced after 90 min under the photocatalysis condition whereas only 40% reduction of toxicity as EC50 was achieved in photolysis condition. The outdoor results using a TiO2/solar system were similar to the TiO2 indoor system, indicating the possibility of applying TiO2/solar system for the treatment of parathion-contaminated water.     

A bifunctionalized dye-sensitized TiO(2) film for efficient degradation of methyl orange under visible light irradiation

A new bifunctionalized TiO(2) film containing a dye-sensitized region and a degradation region was described. A similar structure of dye-sensitized solar cell (DSSC) was fabricated in the dye-sensitized region to accomplish separation of electrons from positive charges, and separation of dye from pollutants to avoid dye decomposition. The bifunctionalized TiO(2) film electrode and anode electrode can degrade methyl orange (MO) in reactors A and B, respectively. The degradation efficiency was enhanced remarkably by an external electrical potential. The decolorization of MO reaches as high as 95% after 2 h visible light irradiation at an external potential of 0.5 V along with a loss of 41% total organic carbon (TOC). The possible reason for the improvement of degradation by external DC potential was discussed. Effects of pH and inorganic salts on the decolorization are present.     

Catalytic action of goethite in the oxidation of 2-chlorophenols with hydrogen peroxide.

The use of goethite and hydrogen peroxide was recently found to effectively oxidise organic compounds. This research was to investigate the effect of adsorption, pH, Fe2+ and Fe3+ on 2-CP oxidation. Results indicated that 2-CP can be decomposed with hydrogen peroxide catalysed by goethite and the oxidation rate increased with decreasing goethite particle size. The optimum oxidation rate was observed at the pH below 3.0. Addition of Fe2+ and Fe3+ can enhance the catalytic oxidation rate of 2-CP very efficiently. The main mechanism of goethite catalysing hydrogen peroxide to oxidise 2-CP may be due to the catalysis of ferrous ions and goethite surface.     

纳米TiO2光催化氧化降解水中有机磷农药的研究

用负载在玻璃纤维布上的锐钛型纳米TiO2作为光催化剂,对水中低浓度的有机磷农药敌敌畏(DDVP)的降解进行了研究.结果表明TiO2浸涂面密度和DDVP的降解效果有很大的关系,当TiO2浸涂面密度为17.5 g/m2时,经210 min催化反应,效果最好,其降解率达到85.22%,而通过在纳米TiO2/UV系统中投加氧化剂H2O2 9 mol/L和O32.52 g/L,在60 min内DDVP降解率分别达到73%和67%,比不投加氧化剂时的DDVP降解率有显著提高.说明该方法对降解有机磷农药具有较好的效果.     

负载型纳米TiO2光催化降解罗丹明B动力学与机理研究

采用负载型纳米TiO2/AC在流化床反应器中降解罗丹明B染料废水。研究了罗丹明B的光催化降解反应动力学与降解机理。结果表明,负载型纳米TiO2光催化降解罗丹明B过程符合一级动力学方程,降解机理首先是罗丹明B分子发色基团苯氨基、羰基键被破坏,然后是无色中间产物的逐渐降解。     

Heterogeneous photocatalytic ozonation of 2,4-D in dilute aqueous solution with TiO2 fiber

Photocatalytic ozonation (O(3)/UV/TiO2) is an emerging oxidation method for recalcitrant organic contaminants in water. However, immobilised TiO2 catalysts suffer from reduced photonic efficiency. Therefore, TiO2 catalysts with excellent mechanical and thermal properties and enhanced photonic efficiencies are sought. This paper aimed to elucidate the mineralisation of low concentration 2,4-D (45.0 microM) by O(3)/UV/TiO2 using the world's first high-strength TiO2 fibre in laboratory batch experiments. 2,4-D degradation and TOC removal followed pseudo first-order reaction kinetic. The removal rates for 2,4-D and TOC in O(3)/UV/TiO2 were 1.5 and 2.4-fold larger than the summation of the values for ozonation (O3)) and photocatalysis (UV/TiO2), respectively. O(3)/UV/TiO2 was characterised by few aromatic intermediates with low abundance, fast degradations of aliphatic intermediates and dechlorination as a major step. The significantly enhanced 2,4-D mineralisation in O(3)/UV/TiO2 was attributed to increased ozone dissolution and decomposition, and reduced electron-hole recombination resulting in large number of hydroxyl radical (*OH) formation from more than one parallel path. The discrepancies in the organic carbon mass budget were attributed to few apparently major unidentified intermediates, while chlorine mass balance was reasonably acceptable. The mineralisation efficiency of O(3)/UV/TiO2 with the TiO2 fibre can further be enhanced by optimisation of experimental design parameters. The new TiO2 fibre is very promising to overcome the problem of reduced efficiency of TiO2 catalyst in an immobilised state.     

Photocatalytic oxidation of methyl ethyl ketone over sol-gel and commercial TiO2 for the improvement of indoor air.

This work focuses on the photocatalytic oxidation of gaseous methyl ethyl ketone chosen as a typical indoor air pollutant. Two types of TiO coatings were prepared and deposited on glass plates: one using the commercial Degussa P25 TiO2 and the other one by sol-gel method. The first objective of this study was to compare different ways of preparing thin films of sol-gel TiO2 coated on glass plates, taking into account their general aspect and their photocatalytic efficiency. Several parameters were tested, such as the stabilising agent, the glass type of the support, the number of coatings and the calcination temperature. One of the synthesised materials was then kept to carry out the following study. The study aimed to assess the influence of TiO2 coating types on the effect of water vapour. This was achieved by performing MEK photocatalytic degradation kinetics under two levels of humidity at a fixed temperature. Experimental results were then modelled by the Langmuir-Hinshelwood equation. The obtained parameters gave specific trends in function of the considered catalyst. The second part of this work was to identify MEK degradation byproducts during its photocatalytic oxidation. The main detected intermediate was acetaldehyde, followed by methyl formate. A MEK degradation pathway was then proposed.     

pH和过氧化氢对水臭氧化生成醛类的影响

本研究提出了饮用水臭氧化过程中作为副产物之一的醛类生成的台架试验结果。研究目的是调查臭氧化对醛类产生的影响。试验结果认为醛类是通过直接途径所形成。用臭氧化法处理时,高的pH值和/或加添过氧化氢可降低醛类生成量。     

Photodegradation of aqueous reactive dye using TiO(2)/zeolite admixtures in a continuous flow reactor

The photocatalytic degradation of an organic dye, i.e. reactive blue 19 (RB19), was studied by employing different TiO(2)/zeolite (TZ) photocatalysts, which have TiO(2)/(TiO(2) + zeolite) weight ratios ranging from 20 to 80%, in a continuous flow system. Three light sources including two UV lights (i.e. λ(max,254 nm) and λ(max,365 nm)) and natural sunlight were used. The results showed that the decoloring rate of RB19 increased as the amount of TiO(2) in the TZ catalyst increased. The photodegradation of RB19 exhibited pseudo-first-order kinetics with respect to the concentration of RB19. Almost 100% of initial RB19 was mineralized under the controlled conditions in this study. And the activities of the prepared photocatalysts were retained after long-term durability experiments. Compared with UV lights (i.e. λ(max,254 nm) and λ(max,365 nm)), the decoloring efficiency of RB19 was significantly increased under natural sunlight illumination, which is likely due to the long-wavelength incident light that photoexcited RB19 and accelerated the degradation rate of RB19 radicals by the UV fraction of sunlight.     

Photocatalytic oxidation of low concentration 2,4-D solution with new TiO2 fiber catalyst in a continuous flow reactor.

Environmental pollution by low concentrations of 2,4-Dichlorophenoxyacetic acid (2,4-D) is a concern these days due to ever increasingly stringent regulations. Photocatalysis with immobilized TiO2 fiber is a promising oxidation method. Laboratory experiments on photocatalytic degradation of 0.045 mmol l(-1) 2,4-D with the world's first high-strength TiO2 fiber catalyst were carried out in a continuous flow reactor in which the degradations were, in general, similar to those with high 2,4-D concentrations investigated elsewhere. Degradation and mineralization of 2,4-D were significantly enhanced with no initial pH adjustments. The rate constants for total organic carbon (TOC) without pH adjustment were about two-fold bigger than the pH adjustment cases. CO2 gas measurement and carbon mass-balance were carried out for the first time, where about 34% organic carbon converted into CO2 gas during four-hour oxidation. 2,4-Dichlorophenol (2,4-DCP), phenol, benzyl alcohol and two unknowns (RT = 2.65 and 3.78 min.) were detected as aromatic intermediates while Phenol was the new aromatic in HPLC analysis. Dechlorination efficiencies were high (> 70%) in all the cases, and more than 90% efficiencies were observed in chloride mass balance. Bigger flow rates and solution temperature fixed at 20 degrees C without pH adjustment greatly enhanced 2,4-D mineralization. These results can be an important basis in applying the treatment method for dioxin-contaminated water and wastewater.     

Effects and mechanism of ozonation for degradation of sodium acetate in aqueous solution

The degradation efficiencies and mechanism of ozonation for the degradation of sodium acetate in aqueous solution were investigated under atmospheric pressure at room temperature (293 K). The effects of the initial pH value, reaction time, and concentrations of HCO3-, CO32-, CaCl2, and Ca(OH)2 on the removal rate of chemical oxygen demand (COD) were studied. The results indicated that ozonation obviously improved the degradation rate of sodium acetate when the pH value of the solution was not less than 8.5. A suitable long reaction time may be helpful in increasing the COD removal rate, and a removal rate of 36.36% can be obtained after a 30-minute treatment. The COD removal rate increased firstly and decreased subsequently with the increase of the HCO3- concentration (from 0 to 200 mg/L), and under the same experimental condition it reached the optimum 34.66% at the HCO3- concentration of 100 mg/L. The COD removal rate was 5.26% lower when the concentration of was 200 mg/L than when there was no HCO3-. The COD removal rate decreased by 15.68% when the CO32- concentration increased from 0 to CO32- 200 mg/L. has a more obvious scavenging effect in inhibiting the formation of hydroxyl radicals than HCO3-. CaCl2 and Ca(OH)2 could increase the degradation efficiency of sodium acetate greatly, and the COD removal rates reached 65.73% and 83.46%, respectively, after a 30-minute treatment, 29.37% and 47.10% higher, respectively, than with single ozone oxidation. It was proved that the degradation of sodium acetate in the ozonation process followed the mechanism of oxidization with hydroxyl free radicals (·OH).     

Advanced H2O2 oxidation for diethyl phthalate degradation in treated effluents: effect of nitrate on oxidation and a pilot-scale AOP operation

One of the objectives of this study was to delineate the effect of nitrate on diethyl phthalate (DEP) oxidation by conducting a bench-scale ultraviolet (UV)/H2O2 and O3/H2O2 operations as suggested in a previous study. We also aim to investigate DEP oxidation at various UV doses and H2O2 concentrations by performing a pilot-scale advanced oxidation processes (AOP) system, into which a portion of the effluent from a pilot-scale membrane bioreactor (MBR) plant was pumped. In the bench-scale AOP operation, the O3 oxidation alone as well as the UV irradiation without H2O2 addition could be among the desirable alternatives for the efficient removal of DEP dissolved in aqueous solutions at a low DEP concentration range of 85+/-15 microg/L. The adverse effect in the UV/H2O2 process was significantly greater than that in the UV oxidation alone, and its oxidation was almost halved by the nitrate. However, the nitrate clearly enhanced the DEP oxidation in the O3 oxidation and O3/H2O2 process. Especially, the addition of nitrate almost doubled the DEP oxidation efficiency in the O3/H2O2 process. The series of pilot-scale AOP operations confirmed that about 30-50% of DEP dissolved in the treated MBR effluent streams was, at least, oxidized by the O3 oxidation alone as well as the UV irradiation without H2O2 addition. The UV photolysis of H2O2 was most effective for DEP degradation with an H2O2 concentration of 40 mg/L at a UV dose of 500 mJ/cm2.     

Effect of ozone, chlorine and hydrogen peroxide on the elimination of colour in treated textile wastewater by MBR.

In treating textile wastewater, the application of membrane bioreactor (MBR) technology showed high efficiency in COD and BOD5 removal. However, insufficient colour removal was achieved for possible reuse. The aim of the work presented in this paper was to test the performance of chemical advanced oxidation on the elimination of the colour downstream of an MBR. To improve the quality of the membrane bioreactor effluent three different oxidation treatments were tested at lab-scale: ozonation, chlorination and hydrogen peroxide oxidation. Colour, COD and BOD5 were controlled in order to assess the effectiveness of each process. For chlorination, even with 250 mg/L (active chlorine) only 80% colour removal (SACin = 14; SACout = 2.8) was achieved which is considered unsatisfactory. For hydrogen peroxide, the colour removal was even poorer; it was just 10% at a concentration of 250 mg/L. In contrast, good results were obtained by ozonation. By using only 38 mg/L within 20 minutes, it was possible to achieve the reuse recommendation with a satisfactory colour removal of 93% (SACin = 14; SACout = 0.98). The results showed that ozonation was the most promising method.     

The denitration pathway of p-nitrophenol in the hydrogen peroxide catalytic oxidation with an Fe(III)-resin catalyst

The liquid-phase hydrogen peroxide catalytic oxidation of p-nitrophenol was performed with an Fe(III)-resin catalyst. The conversion and mineralization of p-nitrophenol was effectively achieved at mild reaction conditions with the Fe(III)-resin catalyst. It was found that the oxidant concentration, pH, and temperature dominated the degradation rate of p-nitrophenol. The denitration pathway of p-nitrophenol was proposed, in which the concentration of H(2)O(2) and temperature showed strong influence on the conversion of nitrite to nitrate. To study the factors influencing the denitration of p-nitrophenol, a comparable kinetic study was attempted to know the possible denitration pathway of p-nitrophenol. The results of this investigation indicated that denitration was the possible step occurring with the decomposition of p-nitrophenol.     

Photocatalytic inactivation of Flavobacterium and E. coli in water by a continuous stirred tank reactor (CSTR) fed with suspended/immobilised TiO2 medium

A photocatalytic continuous stirred tank reactor (CSTR) was built at laboratory scale to inactivate two environmental bacteria strains (Flavobacterium and E. coli) in tap water. Several parameters were found to impact reactor efficiency. Bacterial initial concentration is an important factor in inactivation rate. After 30 minutes of irradiation at 10(8)-10(9) CFU mL(-1) starting concentration, a >5 log reduction was achieved while at 10(4)-10(6) CFU mL(-1) only a 2 log reduction was observed. Water hardness and pH have an important influence on the photocatalytic inactivation process. Soft water, with low Ca(+2) and Mg(+2) at low pH approximately 5.3 resulted in increased inactivation of Flavobacterium reaching >6 orders of magnitude reduction. E. coli and Flavobacterium at pH 5 were inactivated by 3 logs more as compared to pH 7 under similar conditions. pH below TiO2 isoelectric point (approximately 5.6) supports better contact between bacteria and anatase particles resulting in superior inactivation. TiO2 powder suspension was compared with immobilised powder in sol-gel coated glass beads in order to exclude the need for particles separation from the treated water. TiO2 suspension was more effective by 3 orders of magnitude when compared to coated glass beads. An interesting observation was found between the two bacterial strains based on their hydrophobicity/hydrophilicity balance. The more hydrophobic Flavobacterium compared to E. coli was inactivated photocatalytically by >3 logs more then E. coli in the first 30 minutes of irradiation interval. The results indicate the importance of the parameters involved in the contact between TiO2 particles and microorganisms that govern the successful inactivation rate in CSTR.     

Effect of support and second metal in catalytic in-situ generation of hydrogen peroxide by Pd-supported catalysts: application in the removal of organic pollutants by means of the Fenton process

A catalytic system for the generation of H2O2 from formic acid and oxygen at ambient conditions has been developed. Pd-supported catalysts (Pd/C, Pd/TiO2 and Pd/Al2O3) have been tested, showing that for bulk purposes Pd/Al2O3 is more favourable while for in-situ applications Pd/TiO2 seems to be preferable. However, when these catalysts were tested in the in-situ H2O2 generation for the oxidation of phenol by means of the Fenton process (in the presence of ferrous ion), Pd/TiO2 did not demonstrate the expected results, whereas Pd/Al2O3 showed to be an efficient catalyst. Therefore, Pd/Al2O3 is offered as a good catalyst for Fenton's reactions with in-situ generated H2O2. In order to optimize the operating cost of the process, different initial concentrations of formic acid have been tested with Pd/Al2O3, and it has been seen that lowering the initial amount of formic acid favours the efficiency of the process. The effect of the addition of a second metallic (Pt, Au, Fe, Cu) active phase was studied. Concerning H2O2 generation, best results were obtained with a Pd-Au catalyst for bulk production (long time) while for in-situ application Pd-Fe showed interesting results. The Pd-Fe catalyst also performed similarly to the semi-heterogeneous Fenton system involving Pd/Al2O3 and ferrous ion in the degradation of phenol. Therefore, Pd-Fe catalyst offered an interesting prospect for making a full heterogeneous catalyst for Fenton reaction involving in-situ generation of H2O2.     

混凝土中硫酸根离子扩散系数劣化效应研究

鉴于硫酸根离子在扩散过程中会与混凝土材料的水化产物发生化学反应,在扩散方程中引入关于扩散系数的化学反应劣化效应系数,建立了考虑化学反应因素影响的混凝土硫酸根粒子扩散确定性理论模型。该模型解决了Fick第二定理在混凝土中的适应性问题,通过与实验结果进行比较,验证了确定性理论模型可以较好地预测硫酸根离子浓度均值。考虑到混凝土材料在其形成之初的微孔洞、微裂缝等初始缺陷具有随机性,采用高斯随机分布来描述初始扩散系数,研究建立了考虑化学反应因素影响的混凝土硫酸根离子扩散随机性理论模型。通过与实验值对比,验证了随机性理论模型能够较好地预测出硫酸根离子浓度的分布范围。     

Photocatalytic oxidation of humic acid and its effect on haloacetic acid formation potential: a fluorescence spectrometry study

By fluorescence spectrometry method, molecular conformation changes of humic acid (HA) during the photocatalytic oxidation process were studied. Haloacetic acids formation potential (HAAFP) changes during the oxidation process were also measured. The results indicated that aromatic rings of HA decreased and conjugated double bonds were destroyed at the beginning of the process. Meanwhile, organic matter with large molecular weight decomposed into intermediates with smaller molecular weight, such as tryptophan and tyrosine. HA can be degraded almost completely, but not be mineralized thoroughly. Structures of the intermediates were changing during the oxidation process. Molecular structure transformation of HA led to the fluctuation tendency of the HAAFP changes during the photocatalytic oxidation process. HAAFP increased to 1.22 times that in raw water after 30 min of ultraviolet (UV) radiation, and decreased to 0.66 times that in raw water after 60 min of photocatalytic oxidation.     

The adsorption and photodegradation of oxalic acid at the TiO2 surface.

ATR-FTIR measurements in combination with quantum chemical calculations were performed to study chemical reactions taking place at the surface of a thin TiO2 layer immersed in an aqueous oxalic acid solution under UV(A) illumination. It was found that the adsorption of oxalic acid on TiO2 in the dark can be explained in terms of two surface complexes for the anatase phase. Under UV(A) illumination, one of the adsorbed species on the anatase phase preferably undergoes photo-degradation and at the same time more molecules of oxalic acid are adsorbed at the TiO2 surface which is thus enriched in the second complexation mode. The spectral changes observed under UV(A) illumination are explained in the light of different theories: photo-desorption of water molecules as a thermal mechanism induced by the absorption of photons, surface reconstruction, and newly exposed surface area provided by the de-aggregation of the TiO2 particles.     

从1998年洪水看三峡水库的防洪作用

在三峡水库建成后，防洪库容可达２２１．５亿ｍ＾３。若遇１９９８年洪水，利用三峡水库，进行简单的防洪补偿调度，合理利用防洪库容１９０亿ｍ＾３，即可达控制沙市水位不超４５．００ｍ，城陵矶（莲花塘）水位一超３４．４０ｍ的目标，从而极大地减轻长江中下游的防洪压力，若充分发挥水文预报的作用，加强科学预报，防洪效果则更佳。