Search

The effect of Cl^- on photocatalytic degradation (PCD) of pollutants is an important factor since it is ubiquitous in nature. In general, Cl^- showed an inhibition on photodegradation due to its scavenging HO^{·} radicals. In this paper, experiments were carried out to examine the effects of Cl^- on the PCD of Methylene Blue (MB) and Orange II (Oll) in aqueous TiO_2 suspensions under UV light illumination. It was found that low concentration of Cl^- (< 0.01 mol/L) showed little influence on both dyes, however, high concentration of Cl^- (> 0.10 mol/L) had a very different influence on the decolorization of dyes: a significant inhibition for MB but a great promotion for Oll. In the presence of 0.50 mol/L Cl^-, the rate decreased by 70% for MB while increased 7.5-fold for Oll. Furthermore, two bands in the ultraviolet region of Oll were rapidly broken down. The proposed mechanism was discussed in detail. [ABSTRACT FROM AUTHOR]

Phytoremediation has long been recognized as a cost-effective method for the removal of polycyclic aromatic hydrocarbons (PAHs) from soil. A study was conducted to investigate the uptake and accumulation of PAHs in root and shoot of Lolium perenne L. Pot experiments were conducted with series of concentrations of 3.31–378.37 mg/kg for phenanthrene and those of 4.22–365.38 mg/kg for pyrene in a greenhouse. The results showed that both ryegrass roots and shoots did take up PAHs from spiked soils, and generally increased with increasing concentrations of PAH in soil. Bioconcentration factors (BCFs) of phenanthrene by shoots and roots were 0.24–4.25 and 0.17–2.12 for the same treatment. BCFs of pyrene by shoots were 0.20–1.5, except for 4.06 in 4.32 mg/kg treatment, much lower than BCFs of pyrene by roots (0.58–2.28). BCFs of phenanthrene and pyrene tended to decrease with increasing concentrations of phenanthrene and pyrene in soil. Direct uptake and accumulation of these compounds by Lolium perenne L. was very low compared with the other loss pathways, which meant that plant-promoted microbial biodegradation might be the main contribution to plant-enhanced removal of phenanthrene and pyrene in soil. However, the presence of Lolium perenne L. significantly enhanced the removal of phenanthrene and pyrene in spiked soil. At the end of 60 d experiment, the extractable concentrations of phenanthrene and pyrene were lower in planted soil than in non-planted soil, about 83.24%–91.98% of phenanthrene and 68.53%–84.10% of pyrene were removed from soils, respectively. The results indicated that the removal of PAHs in contaminated soils was a feasible approach by using Lolium perenne L. [ABSTRACT FROM AUTHOR]

A greenhouse experiment was carried out to compare differences in potential activities of ammonification, nitrification and denitrification in rhizosphere and bulk soil in a heavy-metal-stressed system. Exchangeable fractions of Cd, Cu and Cr were all higher in the rhizosphere of maize than in bulk soil. Results showed that the mineralization of N in soil was stimulated by low concentration of Cd. Addition of Cd at low levels stimulated the ammonifying and nitrifying activity in soil, while inhibitory influences were shown at high levels. Nitrifying bacteria was proved to be the most sensitive one, whilst the effect on denitrifying bacteria was very limited. Comparing Cd, Cu and Cr(VI) at 20 mg/kg soil, Cd was the most effective inhibitor of ammonification and denitrification, while Cr(VI) had the strongest inhibitory influence on nitrifying activity. Root exudates played important roles on the different exchangeable metal fractions and bacterial activities between rhizosphere and non-rhizosphere. Nitrate was the main form of mineral N in soil, as well as the main form of N absorbed by plants, but the formation and relative absorption of ammonium were promoted in response to high Cd exposure. [ABSTRACT FROM AUTHOR]

The effect of elemental sulfur concentration on bioleaching of Cu, Zn and Pb and loss of fertilizer value from sewage sludge was investigated in flasks by batch experiments. The results showed that the ultimate pH of sludges with 3-5 g/L of sulfur added was about 1.3 and the production of SO42+ had good correlation with the elemental sulfur concentration. The sensitivity of removal efficiency of metals to sulfur concentration was: Pb > Cu > Zn. The sulfur concentration except for 3 - 5 g/L had significant effect on the solubilization of Cu, Pb and Zn. The highest solubilization efficiency for sludge with 3 g/L of sulfur was 87.86% for Cu, 32.72% for Pb and 92.14% for Zn which could make the treated sludge easily meet the metal limitations for land application. The sulfur concentration of 3 g/L was enough for the solubilization of all three heavy metals. The influence of sulfur concentration on solubilization of total nitrogen and potassium from sludge was negligible. but that on solublization of total phosphorus was of great importance. The loss of nitrogen phosphorus and potassium of sludge with 3 g/L of sulfur by bioleaching was 38.2%, 52.1% and 42.8% respectively, and the sludge still remained satisfactory fenilizer value after bioteaching. [ABSTRACT FROM AUTHOR]

The nuisance impact of air pollutant emissions from wastewater pumping stations is a major issue of concern to China. Hydrogen sulfide and ammonia are commonly the primary odor and are important targets for removal. An alternative control technology, biofiltration, was studied. The aim of this study is to investigate the potential of unit systems packed with compost in terms of ammonia and hydrogen sulfide emissions treatment, and to establish optimal operating conditions for a full-scale conceptual design. The laboratory scale biofilter packed with compost was continuously supplied with hydrogen sulfide and ammonia gas mixtures. A volumetric load of less than 150 gH2S/(m³ · d) and 230 gNH3/(m³ · d) was applied for about fifteen weeks. Hydrogen sulfide and ammonia elimination occurred in the biofilter simultaneously. The removal efficiency, removal capacity and removal kinetics in the biofilter were studied. The hydrogen sulfide removal efficiency reached was very high above 99% , and ammonia removal efficiency was about 80% . Hydrogen sulfide was oxidized into sulphate. The ammonia oxidation products were nitrite and nitrate. Ammonia in the biofilter was mainly removed by adsorption onto the carrier material and by absorption into the water fraction of the carrier material. High percentages of hydrogen sulfide or ammonia were oxidized in the first section of the column. Through kinetics analysis, the presence of ammonia did not hinder the hydrogen sulfide removal. According to the relationship between pressure drop and gas velocity for the biofilter and Reynolds number. non-Darcy flow can be assumed to represent the flow in the medium. [ABSTRACT FROM AUTHOR]

Activities at a former Chemistry Triangle in Bitterfeld, Germany. resulted in contamination of groundwater with a mixture of trichloroethylene (TCE) and monochlorobenzene(MCB). The objective of this study was to develop a barrier system, which includes an ORC(oxygen release compounds) and GAC (granular activated carbon) layer for adsorption of MCB and bioregeneration of GAC, a Fe0 layer tot chemical reductive dechlorination of TCE and other chlorinated hydrocarbon in situ. A laboratory=scale column experiment was conducted to evaluate the feasibility of this proposed system. This experiment was performed using a series of continuous flow Teflon columns including an ORC column, a GAC column, and a Fe0 column. Simulated MCB and TCE contaminated groundwater was pumped upflow into this system at a flow rate of 1.1ml/min. Results showed that 17%-50% of TCE and 28%-50% of MCB were dissipated in ORC column. Chloride ion, however, was not released, which suggest the dechlorination do not happen in ORC column. In GAC column, the adsorption of contaminants on activated carbon and their induced degradation by adapted microorganisms attached to the carbon surface were observed. Due to competitive exchange processes. TCE can be desorbed by MCB in GAC column and further degraded in iron column, The completely dechlorination rate of TCE was 0.16-0.18 cm-1, 1-4 magnitudes more than the formation rate of three dichloroethene isomers. Cis-DCE is the main chlorinated product, which can be cumulated in the system, not only depending on the formation rate and its decaying rate, but also the initial concentration of TCE. [ABSTRACT FROM AUTHOR]

Spatial distribution of heavy metals, arsenic and organic matter in recent sediments In the Hangzhou section of the Grand Canal and their relationships were analyzed. The results showed that the concentrations of heavy metals and organic matters varied widely along the canal, and the average geological accumulation factors decreased in the following orders: organic carbon (2.6). zinc (2.1). cadmium (2.0), copper (1.5), lead (1.1.), nitrogen (0.9), mercury (0.8), phosphorus (0.4), arsenic (0.2) and chromium (0). Content of heavy metals and organic carbon in the top 10 cm layer were lower than that of lower layers, except for mercury and organic carbon in the S9 section. Contents of organic carbon in the top 50 cm layer of the mud sediments are significantly higher than those underneath. In the bottom mud layer, there is a concentration peak of the pollutants. In the mud sediments of the canal, cadmium mainly occurred in the Fe and Mn oxide fraction, copper in the organic fraction, lead in the Fe and Mn oxide fraction, and zinc in the carbonate and the Fe and Mn oxide fraction. [ABSTRACT FROM AUTHOR]

The reduction of nitrate contaminant in groundwater has gained renewed and intensive attention due to the environmental problems and health risks. Catalytic denetrification presents one one of the most promising approaches for the removal of nitrate from water. Catalytic nitrate reduction from water by powder catalysts and catalytic membrane in a batch reactor was studied. And the effects of the initial concentration, the amounts of catalyst, and the flux H[sub2] on the nitrate reductiion were also discussed. The results demonstrated that nitrate reduction activity and the selectivity to nitrogen gas were mainly controlled by diffusion limitations and the mass transfer of the reactants. The selectivity can improved while retaining a high catalytic activity under conrolled diffusion condition or the intensification of the mass transfer, and a good reaction condition. The total nitrogen removal efficiency reached above 80%. Moreover, catalytic membrane can create a high effective gas/liquid/solid interface, and show a good selectivity to nitrogen in comparative with the power catalyst, the selectivity to nitrogen was improved from 73.4% to 89.4%. [ABSTRACT FROM AUTHOR]

Phytolacca acinosa Roxb. (P. acinosa) is a recently discovered manganese hyperaccumulator plant from southern China. It is a good candidate for phytoremediation of manganese(Mn) polluted soil for its high biomass and fast growth. Knowledge of the tissue localization and identification of heavy metals can provide essential information on metal toxicity and bioaccumulation mechanisms. Synchrotron radiation X-ray fluorescence spectroscopy (SRXRF) microprobe was used in this study to investigate the cellular distributions of Mn and other elements in root, stem, leaf, petiole and midrib ofP. acinosa. The highest Mn content was found in the vascular tissues of root, stem, petiole and midrib. Cortex in root played a key role in Mn absorption and Mn was limited in the vascular bundle during the process of transportation in stem. Moreover, Mn content in leaf epidermis was higher than that in mesophyll, which suggested that the sequestration of Mn in leaf epidermis might be one of the detoxification mechanisms of P. acinosa. The significance of other elemental (such as P, S, K, Ca, Fe, Zn and Cu) distribution patterns and the correlation with Mn were also discussed. [ABSTRACT FROM AUTHOR]

Humic substrates are a major fraction of sediment organic matters, and the sorption of hydrophobic organic chemicals by humic substrates influences their behavior and fate in sediment. In this paper, organic matters were divided into non-humic substrates and humic substrates. Non-humic substrates include acid leaching fraction, acid extracted fraction, and lipid; humic substrates were fractionated into Ca-binding-FA (fulvic acid), Ca-binding-HA (humic acid), oxide-FA, oxide-HA, and humin. To study the effect of organic fractions on sorption properties, sorption kinetic and equilibrium sorption experiments of phenanthrene and pentachlorophenol (PCP) in five sediments were carried out. The results showed that the contents of acid leaching fraction and oxide-binding-HA were the main fractions to affect the sorption rate constant, and for the sorption capacity of phenanthrene, humin was the major fraction, followed by oxide-binding-HA, oxide-binding-FA, and so on. While for PCP, the factors of influence on sorption capacity were mainly CEC, Ca-binding-FA, and Ca-binding-HA. [ABSTRACT FROM AUTHOR]

For TiO_2 heterogeneous reaction, the reaction site and the detailed mechanism are interesting and controversy topics. In this paper, effects of surface fluorination of TiO_2 on the photocatalytic degradation of an azo dye, Orange G(OG) under UV or visible light irradiation were investigated, and the possible reaction site and mechanism were elucidated. The adsorption of OG on TiO_2 was nearly inhibited by fluoride but its UV light induced photodegradation rate was greatly increased by a factor of about 2.7, which was due to the more generated free hydroxyl radicals. It supported the views that fluoride could desorb the oxidant species from surface and that the reaction sites could move to the bulk solution. In TiO_2/Vis system, the observed inhibition effects of fluorination could be interpreted by the competitive adsorption, which provided additional evidences that the visible light sensitized photodegradation of dye pollutants on the catalyst surface. [ABSTRACT FROM AUTHOR]