Structure and thermal stability of toxic chromium(VI) species doped onto TiO2 powders through heat treatment

Chromium(VI)-containing sorbents in the form of sludge or solid residue from treatment processes are often landfilled or used as fill materials, therefore the long-term stability of metal binding is important. The reduction of Cr(VI)–Cr(III) through heat treatment may be a useful detoxification method. After heating at 500, 900, 1000, and 1100 °C for 4 h, the transformation of chemical states of chromium on 105 °C-dried, 7.9% Cr(VI)-doped TiO₂ powders was studied on the basis of surface area measurements, scanning electron microscopy (SEM) images, X-ray diffraction (XRD), and extended X-ray absorption fine structure (EXAFS) spectra. It was shown that Cr(VI) was reduced to Cr(III) in the Cr(VI)-doped samples after heating within 500–900 °C. The present results also suggested that the chromium octahedral was bridged to the titanium tetrahedral and was incorporated in TiO₂ minerals formed after 1000 °C treatment.     

Kinetic studies on the adsorption of phenol, 4-chlorophenol,and 2,4-dichlorophenol from water using activated carbons

This study uses rate parameters in pseudo-first-order (PFO) and pseudo-second-order (PSO) equations (k₁ and k₂q_e, respectively) to judge the extent for approaching equilibrium in an adsorption process. Out of fifty-six systems collected from the literature, the adsorption processes with a k₂q_e value between 0.1 and 0.8 min^?1 account for as much as 70% of the total. These are classified as fast processes. This work compares the validity of PFO and PSO equations for the adsorption of phenol, 4-chlorophenol (4-CP), and 2,4-dichlorophenol (2,4-DCP) on activated carbons prepared from pistachio shells at different NaOH/char ratios. The activated carbons, recognized as microporous materials, had a surface area ranging from 939 to 1936 m²/g. Findings show that the adsorption of phenol, 4-CP, and 2,4-DCP on activated carbons had a k₂q_e value of 0.15–0.58 min^?1, reflecting the fast process. Evaluating the operating time by rate parameters revealed that k₂q_e was 1.6–1.8 times larger than k₁. These findings demonstrate the significance of using an appropriate kinetic equation for adsorption process design.     

Effects of composing on sorption capacity of bagasse-based chars

A fresh bagasse sample (0-month) and two composted bagasse and pig manure mixed samples (1-month and 6-month) were used to produce carbon chars. Sample pyrolysis showed greater carbon char yields were obtained from the compost samples than from the bagasse sample. Fourier transform infrared spectra suggested that the chemical structures of the bagasse sample and the two compost samples were quite different, but that the three carbon chars obtained from those precursors were similar. Among the three pyrolyzed chars, the 0-month bagasse char displayed the largest sorption capacity of 3333 mg kg^?1 for the hydrophilic pollutant phenol, presumably resulting from its greater carbon content and O/C ratio. However, the sorption capacities for the hydrophobic pollutant naphthalene of the tow compost chars (3-month, 2001 mg kg^?1; 6-month, 1667 mg kg^?1) were greater than that of the 0-month bagasse char (1428 mg kg^?1). The results indicate that the compost chars had a greater preferential affinity for naphthalene than that in the bagasse char, suggesting that the compost chars possessed greater hydrophobicity.     

Site-specific phosphorus application based on the kriging fertilizer-phosphorus availability index of soils

Site-specific phosphorus management is done to optimize crop production and minimize P loss from soils. The spatial variability of the available P prior to fertilizer application and the P-fixation tendency of soil both need to be taken into account for variable-rate P application. The objectives of this research were to document the spatial variability of the fertilizer-P availability index, which shows the P-fixation tendency, and to develop a strategy that takes the spatial distribution of this index into account for site-specific phosphorus application. In this study, the spatial patterns of the fertilizer-P availability index were characterized by using geostatistics. The ordinary kriging was used for spatial interpolation of the fertilizer-P availability index. Because the fertilizer-P availability index of soil is related to oxalate-extractable Fe and Al and because measuring oxalate-extractable Fe and Al is much easier than directly determining the fertilizer-P availability index, the spatial distribution of the fertilizer-P availability index can be obtained using the oxalate-extractable Fe and Al data. The spatial distribution of Olsen-extractable P, which was used to measure the available-P status prior to fertilizer-P application, was also estimated by using ordinary kriging. The required fertilizer-P amounts were then determined using the kriging estimates of the fertilizer-P availability index and Olsen-extractable P. A fertilizer-P recommendation map for the 430-ha study site in Changhua county, Taiwan was generated by using this approach for illustration. The proposed method for generating fertilizer-P recommendation maps can be used for variable-rate application to maintain an adequate P status for crop production and to potentially reduce the P loss from soils.     

Study On the Hydraulic Characteristics of Taichung Harbour in Taiwan

For this study, field measurements of current profiles, buoy trajectories and the lag of two tidal stations were performed to explore the flow characteristics of Taichung Harbour. in order to distinguish the effects of wind drift current on circulation inside Taichung Harbour, field surveys during both summer and monsoon (winter) season were completed separately. the speed of the drift current was about 3.5% that of the, wind speed, based on the field data. the horizontal dispersion coefficients were close to Bowden's (1965) formula for the tidal current. the water temperature showed a two-layer profile, with the mixing thickness about 4 to 6 metres for the upper layer. the corresponding Richardson number was about 70. the tidal lag between the two tidal stations was 9.68 minutes. All the results agree well with the theoretical results.     

两相分配式生物反应器处理高盐废水中的苯酚

采用新型两相分配式生物反应器(TPPB)和前期研究得到的高效苯酚降解菌对高盐废水中苯酚的降解进行研究,研究中确定煤油为反应系统的最佳有机溶剂,并考察了废水苯酚含量、废水盐度以及搅拌器搅拌速度对苯酚降解的影响。结果表明,反应系统能正常降解苯酚含量为1 000～2 500 mg/L的高盐苯酚废水;反应系统在含盐量为100 g NaCl/L、搅拌速度为50 r/min的运行工况条件下,降解时间缩短为52 h,总酚去除率为20.58 mg/(L.h)。     

The structure of turbulence near a tall forest edge: the backward-facing step flow analogy revisited

Flow disturbances near tall forest edges are receiving significant attention in diverse disciplines including ecology, forest management, meteorology, and fluid mechanics. Current theories suggest that near a forest edge, when the flow originates from a forest into a large clearing, the flow retains its forest canopy turbulence structure at the exit point. Here, we propose that this framework is not sufficiently general for dense forested edges and suggest that the flow shares several attributes with backward-facing step (BFS) flow. Similar analogies, such as rotor-like circulations, have been proposed by a number of investigators, though the consequences of such circulations on the primary terms in the mean momentum balance at the forest clearing edge have rarely been studied in the field. Using an array of three triaxial sonic anemometers positioned to measure horizontal and vertical gradients of the velocity statistics near a forest edge, we show that the flow structure is more consistent with an intermittent recirculation pattern, rather than a continuous rotor, whose genesis resembles the BFS flow. We also show that the lateral velocity variance, v'2, is the moment that adjusts most slowly with downwind distance as the flow exits from the forest into the clearing. Surprisingly, the longitudinal and vertical velocity variances (u'2 and w'2) at the forest edge were comparable in magnitude to their respective values at the center of a large grass-covered forest clearing, suggesting rapid adjustment at the edge. Discussions on how the forest edge modifies the spectra and co-spectra of momentum fluxes, effective mixing length, and static pressure are also presented.     

Adsorption of phenol and its derivatives from water using synthetic resins and low-cost natural adsorbents: a review

In this article, the technical feasibility of the use of activated carbon, synthetic resins, and various low-cost natural adsorbents for the removal of phenol and its derivatives from contaminated water has been reviewed. Instead of using commercial activated carbon and synthetic resins, researchers have worked on inexpensive materials such as coal fly ash, sludge, biomass, zeolites, and other adsorbents, which have high adsorption capacity and are locally available. The comparison of their removal performance with that of activated carbon and synthetic resins is presented in this study. From our survey of about 100 papers, low-cost adsorbents have demonstrated outstanding removal capabilities for phenol and its derivatives compared to activated carbons. Adsorbents that stand out for high adsorption capacities are coal-reject, residual coal treated with H3PO4, dried activated sludge, red mud, and cetyltrimethylammonium bromide-modified montmorillonite. Of these synthetic resins, HiSiv 1000 and IRA-420 display high adsorption capacity of phenol and XAD-4 has good adsorption capability for 2-nitrophenol. These polymeric adsorbents are suitable for industrial effluents containing phenol and its derivatives as mentioned previously. It should be noted that the adsorption capacities of the adsorbents presented here vary significantly depending on the characteristics of the individual adsorbent, the extent of chemical modifications, and the concentrations of solutes.     

Using sequential indicator simulation to assess the uncertainty of delineating heavy-metal contaminated soils

Mapping the spatial distribution of soil pollutants is essential for delineating contaminated areas. Currently, geostatistical interpolation, kriging, is increasingly used to estimate pollutant concentrations in soils. The kriging-based approach, indicator kriging (IK), may be used to model the uncertainty of mapping. However, a smoothing effect is usually produced when using kriging in pollutant mapping. The detailed spatial patterns of pollutants could, therefore, be lost. The local uncertainty of mapping pollutants derived by the IK technique is referred to as the conditional cumulative distribution function (ccdf) for one specific location (i.e. single-location uncertainty). The local uncertainty information obtained by IK is not sufficient as the uncertainty of mapping at several locations simultaneously (i.e. multi-location uncertainty or spatial uncertainty) is required to assess the reliability of the delineation of contaminated areas. The simulation approach, sequential indicator simulation (SIS), which has the ability to model not only single, but also multi-location uncertainties, was used, in this study, to assess the uncertainty of the delineation of heavy metal contaminated soils. To illustrate this, a data set of Cu concentrations in soil from Taiwan was used. The results show that contour maps of Cu concentrations generated by the SIS realizations exhausted all the spatial patterns of Cu concentrations without the smoothing effect found when using the kriging method. Based on the SIS realizations, the local uncertainty of Cu concentrations at a specific location of x', refers to the probability of the Cu concentration z(x') being higher than the defined threshold level of contamination (z(c)). This can be written as Prob(SIS)[z(x')>z(c)], representing the probability of contamination. The probability map of Prob(SIS)[z(x')>z(c)] can then be used for delineating contaminated areas. In addition, the multi-location uncertainty of an area A,delineated as contaminated based on the probability map of Prob(SIS)[z(x')>z(c)], can be calculated to assess the reliability of delineation. Multi-location uncertainty refers to the probability of Cu concentrations in several locations, x'(1), x'(2), em leader, x'(m,) in the area A, being higher than the threshold (z(c)) as denoted by Prob(SIS)[z(x'(1))>z(c), z(x'(2))>z(c), em leader, andz(x'(m))>z(c)] or Prob(SIS)[z(A)>z(c)]. The multi-location uncertainty Prob(SIS)[z(A)>z(c)], obtained from the SIS, can be used to assess the reliability of delineation for regions suspected of contamination, (A), which has been delineated as contaminated. Reliance on this information facilitates the decision making process in determining which areas are contaminated and require cleanup action.