Photooxidation of azo dye reactive black 5 using a novel supported iron oxide: heterogeneous and homogeneous approach.

Photooxidation of azo dye Reactive Black 5 (RB5) by H202 was performed with a novel supported iron oxide in a batch reactor in the range of pH 2.5-6.0. The iron oxide was prepared through a fluidized-bed reactor (FBR) and much cheaper than the Nafion-based catalysts. Experimental results indicate that the iron oxide can significantly accelerate the degradation of RB5 under the irradiation of UVA light (wavelength = 365 nm). An advantage of the catalyst is its long-term stability, which was confirmed through using the catalyst for multiple runs in the degradation of RB5. In addition, this study focused mainly on determining the proportions of homogeneous catalysis and heterogeneous catalysis in the batch reactor. Conclusively, although heterogeneous catalysis contributes primarily to the oxidation of RB5 during pH 4.5-6.0, the homogeneous catalysis is of increasing importance below pH 4.0 because of the Fe ions leaching from the catalyst to solution.     

Hydraulic performance of a modified constructed wetland system through a CFD-based approach

Low-cost household technologies, as horizontal subsurface flow constructed wetlands, are important to address water and sanitation needs in the Asia-Pacific region in a more integrated and sustainable manner, and a better understanding of these technologies would benefit their engineering design. Computational Fluid Dynamics (CFD) simulations of a modified constructed wetland system (EvaTAC) were undertaken to determine empirical effects of geometric and flow parameters on the hydraulic performance and the effluent pollutant fraction. The CFD model was validated by comparing the computed residence time distribution (RTD) with experimental results. RTD functions were then used to quantify hydraulic indexes: short-circuiting, mixing, and moment. The EvaTAC is composed of an evapotranspiration and treatment chamber (CEvaT) and a horizontal subsurface flow constructed wetland (HSSF-CW). For the CEvaT, length and the interaction between length and flow rate were the most important factors for the hydraulic efficiency. For the effluent pollutant fraction, the most important factor was flow rate. For the HSSF-CW, the strongest influence on the hydraulic efficiency was the length. Baffles and the interaction between length and baffles also had significant statistical influence on the hydraulic efficiency. Furthermore, the results showed that flow rate, length, and the interaction between flow rate and length influenced the effluent pollutant fraction significantly. Finally, a poor correlation between hydraulic indexes and effluent pollutant fraction was obtained, indicating that the hydraulic indexes are not good predictors of the effluent pollutant fraction.     

On a QSAR approach for the prediction of priority compound degradation by water treatment processes

Emerging (chemical) substances are increasingly found in water sources and must be removed by water treatment systems. However, the treatment efficiency regarding these substances is often unknown. A promising approach is using QSARs (quantitative structure activity relationships) or QSPRs (quantitative structure property relationships) to correlate the existing knowledge of a compound's chemical structure to water treatment process properties, such as a biological activity or physico-chemical property. As UV/H(2)O(2) treatment of water is an important barrier against priority pollutants, a QSAR model has been developed for the prediction of a typical physico-chemical property: i.e. hydroxyl radical reaction constants. Hydroxyl radicals are highly reactive and therefore largely responsible for a compound's degradation during UV/H(2)O(2) treatment. A good correlation is found for the training data set. Chemical parameters that were related to charge on C atoms and topology of the compound were found to be important for the hydroxyl radical rate constants. So far, these results look promising, but further research is still required to increase the predictability of the model and to develop QSAR models for other physico-chemical properties.     

改性花生壳和木屑对水中活性艳红的吸附研究

用经过磷酸改性的花生壳和木屑制成混合吸附剂对水中活性艳红K-2BP进行吸附研究,通过静态试验系统地考察了混合吸附剂中改性花生壳和木屑的质量比、混合吸附剂的投加量、p H、温度和振荡速率等重要因素对K-2BP吸附效果的影响,并对吸附机理进行了探讨。研究结果表明:改性花生壳和木屑对10 mg/L K-2BP吸附的最佳条件为:改性花生壳和木屑的质量比1∶3.5,混合吸附剂的投加量0.9 g,温度328 K,p H值14,振荡速率120r/min,水中K-2BP的去除率可达98.6%,影响因素中p H值的影响最大。Langmuir吸附模型和伪二级动力学模型能较好地描述混合吸附剂对水中K-2BP的吸附过程,理论的最大吸附量为10.83 mg/g,吸附过程为吸热反应,可自发进行,因此改性花生壳和木屑吸附K-2BP技术在实际污染处理中具有良好的应用前景。     

改性玉米芯吸附水中重金属离子的实验研究

以玉米芯做原料,用酒石酸改性,利用改性玉米芯吸附水中的Cu2＋ 和Pb2＋实验结果表明,实验中改性玉米芯吸附水中的Cu2＋ 和Pb2＋的吸附条件为：pH为5,吸附时间为120min,初始浓度为50mg／L,投加量为0．5g,在此条件下,改性玉米芯对Cu2＋ 和Pb2＋的吸附去除率分别为68％和94％,普通玉米芯对Cu2＋和 Pb2＋的吸附去除率分别为25％和65％。吸附过程更加能够符合准二级动力学方程,吸附规律能够更好地用Freundlieh方程所描述。改性玉米芯对重金属离子有选择吸附的能力,Pb2＋更加容易被吸附。本实验对于重金属的去除具有一定的参考价值。     

Heterogeneous photo-catalysis system for the degradation of azo dye Reactive Black 5 (RB5)

This study investigated a heterogeneous photo-catalysis system by introducing a novel brick supported iron oxide (denoted as B1) for the heterogeneous photoassisted degradation of Reactive Black 5 (RB5) at pH value from 3 to 7 in a three-phase (gas-liquid-solid) fluidized bed reactor (3P-FBR). Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD) and N(2) adsorption/desorption were used to characterize the B1 catalyst. The in situ formation of hydrogen peroxide and the depletion of oxalic acid by photochemical cycle of Fe(III)-oxalate complex under UVA light (λ = 365 nm) were studied. The effects of the solution pH and the concentration of oxalic acid on the degradation of RB5 are elucidated. About 90% decolourization was measured and 80% of the total organic carbon (TOC) was eliminated at pH 5.0 after 120 min for 20 mg/L RB5 in presence of 10 g/L B1 catalyst, 30 mg/L oxalic acid under 15 W UVA light. A mechanism for the photocatalytic degradation of RB5 over B1 catalyst is proposed.     

氧化钴修饰活性炭微波催化降解染料废水的工艺研究

经预处理、超声浸渍、焙烧制备出载钴活性炭.采用热重分析,载钴活性炭的失重温度为410℃,较活性炭提高了30℃;X-射线衍射分析,载钴活性炭在2θ为20.9°、37.1°、43.0°时出现吸收峰,活性炭表面晶型出现了掺杂的CoO立方晶系的衍射峰.经电镜扫描分析,CoO颗粒的存在导致载钴活性炭表面缺陷增多.在所定工艺参数下,载钴活性炭催化微波降解染料水溶液10 min,酸性染料及阳离子染料水溶液的脱色率87.95％ ～ 96.18％,CODcr去除率78.31％～89.70％,降解过程可用一级化学反应动力学方程拟合.实验表明:氧化钴修饰活性炭在微波催化作用下对染料废水具有良好的降解效果.     

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.     

新型功能化改性生物质吸附剂的制备及其对重金属铜的吸附性能研究

为有效解决自然水体中重金属污染的问题,以来源广泛、成本低廉、可再生的废弃生物质材料(花生壳、玉米芯、白果壳、树皮等)为基体,通过表面预处理、高温炭化以及后功能化改性(包括硫酸、硝酸、柠檬酸、高锰酸钾活化)等工艺制备了一系列高效多孔生物吸附剂材料.结果表明,经过高锰酸钾氧化改性的生物吸附剂(花生壳、玉米芯、白果壳、树皮)...     

Photodegradation of 4-chloronitrobenzene in the presence of aqueous titania suspensions in different gas atmospheres

The photocatalytic degradation of 4-chloronitrobenzene (4-CNB) was carried out using Degussa P25 TiO(2) as photocatalyst in three different gas atmospheres: nitrogen, oxygen, and ozone. The total organic carbon (TOC) and inorganic anions including chloride, nitrite, and nitrate anions were measured to monitor the mineralization processes, while the degradation of 4-CNB and the formation of intermediates were followed by liquid chromatography-mass spectrometry (LC/MS). Results showed that the photocatalytic efficiency followed the order of TiO(2)/UV/N(2) < TiO(2)/UV/O(2) < TiO(2)/UV/O(3), which was further proved by evaluating the reaction activities using electron paramagnetic resonance (EPR) spin trapping technique. Chlorine atom, nitro group and hydrogen atom of the benzene ring could be displaced by hydroxyl radical (?OH) leading to the formation of chloride, nitrite (III) anions and a variety of phenols, then the nitrite (III) anions were further oxidized to nitrate (V) anions. 4-Nitrophenol and 5-chloro-2-nitrophenol were identified and quantified in both of the TiO(2)/UV/N(2) and TiO(2)/UV/O(2) processes while no aromatic intermediates were monitored in the process of TiO(2)/UV/O(3).     

小水电工程:新思路与新方法,对其未来至关重要吗?

一直以来。小水电工程就不是一项简单或琐碎的工作。实现经济指标、解决技术问题是其发展的主要动力。由于生态的制约。至少在未来若干个20a里。小水电不断增加的发展需求将不再与先前制定的战略相适应。就小水电设计、建设过程、理念、所有权和定位而论。新的挑战需要新的思路。有时寻找新的思路仅仅需要对一些想当然的概念进行批判性反思。人们必须超越技术能力和传统思想的束缚。最终目标是进一步开发水电资源。本文是根据作者2005年在挪威斯塔万格的一次大会主旨发言撰写的。[编者按]     

Mobile-bed aggradation and degradation in a narrow flume: Laboratory experiments and numerical simulations

Aggradation and degradation phenomena in fluvial beds having uniform sediments are explored experimentally and simulated numerically. Laboratory experiments were conducted in a narrow mobile-bed flume for different sediment sizes, flow discharges and bed slopes. The flume had a cross-section of curved wall and flat bed, where the shear stress distribution is not same on the bed and the walls. Tests were carried out in two conditions: (1) equilibrium condition, where, once the steady and uniform flow conditions were achieved for a given slope and discharge, the channel was fed with variable sediment discharges until the bed-load sediment transport achieved an equilibrium condition; and (2) non-equilibrium condition, where the sediment feeding was instantaneously stopped (degradation tests) or increased (aggradation tests) and the bed levels were measured over time. Experimental results enabled assessing the deposition and erosion rates and determining the empirical power law for the bed-load discharge. Numerical simulations were then performed with the Double Order Approximation (DORA) model, which solves the one-dimensional shallow water equations governing a free surface gradually varied unsteady flow on mobile beds. As closure relationship, three bed-load formulae were implemented in the numerical code: the Ackers, P. [1984. Sediment transport in sewers and the design implications. In: Proceedings of the International Conference on Planning, Construction, Maintenance and Operation of Sewerage Systems, Reading, England, BHRA (Cranfield), pp. 215–230.] and Meyer-Peter, E., Müller, R. [1948. Formulas for Bed-Load Transport. Report on the Second IAHR Meeting, Stockholm, Sweden, pp. 39–64.] ones and a formula empirically derived at equilibrium in the laboratory tests. The results show that the DORA model can reproduce the bed profiles over time except the local scouring at the transition between fixed and mobile bed. In particular, in the best simulations obtained by using the empirical bed-load power law, the time evolution of bed profiles is in good agreement with the measured data of aggradation and degradation tests, having small average relative errors.     

Diphasic transfer of oxygen in vertical flow filters: a modelling approach

Oxygen renewal, as a prominent phenomenon for aerobic bacterial activity, deeply impacts vertical flow constructed wetland (VFCW) treatment efficiency. The authors introduce a multiphase model able to simulate oxygen transfer in VFCWs. It is based on a two-phase flow module, and a transport module. The transport module is able to deal with convection/diffusion phenomena, inter-phase (air-water) mass exchange, and first-order kinetics. The first results displayed for the air phase allow us to draw the following ideas on the design of vertical filters. The ponding phenomenon is more efficient for oxygen renewal than non-ponding batch loading: it provides a higher value, sooner, and deeper in the filter. In non-colonised filters and for standard batch loading, oxygen convection in the air phase is predominant for oxygen renewal. The seepage front limits oxygen renewal through the bottom of the filter and leads to an insufficient oxygen concentration on the lowest part of the filter.     

Isolation and screening of heavy metal resistant bacteria from wastewater: a study of heavy metal co-resistance and antibiotics resistance

The uncontrolled discharges of wastes containing a large quantity of heavy metal create huge economical and healthcare burdens particularly for people living near that area. However, the bioremediation of metal pollutants from wastewater using metal-resistant bacteria is a very important aspect of environmental biotechnology. In this study, 13 heavy metal resistant bacteria were isolated from the wastewater of wadi El Harrach in the east of Algiers and characterized. These include zinc-, lead-, chromium- and cadmium-resistant bacteria. The metal-resistant isolates characterized include both Gram-negative (77%) and Gram-positive (23%) bacteria. The Minimum Inhibitory Concentration (MIC) of wastewater isolates against the four heavy metals was determined in solid media and ranged from 100 to 1,500 μg/ml. All the isolates showed co-resistance to other heavy metals and antibiotic resistance of which 15% were resistant to one antibiotic and 85% were multi- and bi-antibiotics resistant. The zinc-resistant species Micrococcus luteus was the much more heavy metal resistant. The results of toxicity tests on Vibrio fischeri showed that the DI(50) (5 min) as low as 0.1 carried away luminescence inhibition greater than 50%.     

Estimation of kinetic parameters of a model for deammonification in biofilms and evaluation of the model.

A systematic approach to estimate and evaluate parameters for deammonification in biofilms from available experimental data was evaluated. Parameter estimation was based on a regional steady state sensitivity analysis to select relevant parameters and design of experiments based on a local identifiability analysis. The calibrated model was evaluated under different experimental conditions. Nine of the 16 kinetic and stoichiometric parameters had a significant influence on model predictions. Of these nine parameters only six kinetic parameters were identifiable from batch experiments regardless of the experimental design. More parameters were not identifiable due to high correlations between growth rates and the corresponding affinity constant for oxygen. Data from a batch experiment at 2 mg/L dissolved oxygen (DO) were used to estimate inactivation rates and affinity constants for oxygen for ammonium oxidisers (AO), nitrite oxidisers (NO) and anaerobic ammonium oxidisers (AN). In addition, it was found that not only kinetic and stoichiometric parameters but also the external mass transfer resistance significantly affected model predictions. The resulting model was able to reproduce batch test and continuous reactor operation where DO concentrations were similar to those in the batch experiment used for parameter estimation. However, the model overestimated deammonification for a batch experiment at a much higher DO concentration (5 mg/L). Thus, parameter values that are identifiable and are estimated for given environmental conditions may not necessarily be valid for significantly different experimental conditions.     

Effects of in-sewer processes: a stochastic model approach.

Transformations of organic matter, nitrogen and sulfur in sewers can be simulated taking into account the relevant transformation and transport processes. One objective of such simulation is the assessment and management of hydrogen sulfide formation and corrosion. Sulfide is formed in the biofilms and sediments of the water phase, but corrosion occurs on the moist surfaces of the sewer gas phase. Consequently, both phases and the transport of volatile substances between these phases must be included. Furthermore, wastewater composition and transformations in sewers are complex and subject to high, natural variability. This paper presents the latest developments of the WATS model concept, allowing integrated aerobic, anoxic and anaerobic simulation of the water phase and of gas phase processes. The resulting model is complex and with high parameter variability. An example applying stochastic modeling shows how this complexity and variability can be taken into account.     

Iron cycling in a littoral freshwater beach: Implications for floc trace metal dynamics

This field-based study demonstrates that highly dynamic trace metal (Ag, Co, Cu and Pb) behavior in suspended floc and the sediment surface fine-grained lamina (SFGL) is linked specifically to Fe mineral cycling between these two compartments driven by rapidly fluctuating energy regimes in a shallow, littoral beach of Lake Ontario. Results reveal distinct, Fe mineral controls on trace metal sequestration patterns under quiescent conditions. Higher metal sequestration occurred in floc associated with amorphous Fe oxyhydroxides (FeOOH), while less reactive crystalline Fe oxides (FeOx) dominated bed metal sequestration. Spatial shifts in energy regime governing floc settling and sediment erosion controlled the mixing of FeOOH and FeOx, resulting in discernible, hydrodynamic-dependent floc and SFGL trace metal associations. Low turbulence offshore limited compartment mixing, resulting in enrichment of FeOOH and metals in floc and SFGL over bulk bed sediments. In contrast, higher turbulence nearshore increased bed erosion resulting in less distinct floc and SFGL-FeOOH/metal abundances and partitioning. Diurnal shifts in energy regime impacting floc and SFGL geochemistry were observed nearshore. Accumulation of FeOOH and trace metals occurred in the SFGL under calm morning conditions, while diurnal wind-induced waves rapidly re-cycled the SFGL back into the overlying water-column. Post mixing, re-suspended FeOOH and smaller floc particulates entrained within a higher photosynthetically-induced pH water-column increased overall floc trace metal uptake. Taken together, these findings demonstrate highly dynamic linkages between energy regime and physico-chemistry impacted Fe mineral cycling resulting in observable compartment-specific trace metal partitioning patterns for littoral floc and surficial sediments in beach environments.     

Hydrogen sulfide emission in sewer networks: a two-phase modeling approach to the sulfur cycle.

Wherever transport of anaerobic wastewater occurs, potential problems associated with hydrogen sulfide in relation to odor nuisance, health risk and corrosion exist. Improved understanding of prediction of hydrogen sulfide emission into the sewer atmosphere is needed for better evaluation of such problems in sewer networks. A two-phase model for emission of hydrogen sulfide along stretches of gravity sewers is presented to estimate the occurrence of both sulfide in the water phase and hydrogen sulfide in the sewer atmosphere. The model takes into account air-water mass transfer of hydrogen sulfide and interactions with other processes in the sulfur cycle. Various emission scenarios are simulated to illustrate the release characteristics of hydrogen sulfide.     

Effects of benthic algae on release of soluble reactive phosphorus from sediments: a radioisotope tracing study

To evaluate the effect of benthic algae on soluble reactive phosphorus(SRP) release from sediments in shallow lakes, experiments on SRP release with and without benthic algae in sediment cores and an experiment on SRP uptake by benthic algae were conducted using the radioisotope(32P) tracing method. The dissolved oxygen(DO) concentration in sediment cores was also investigated. The results show that benthic algae effectively reduce the release of SRP from sediments to overlying water. The uptake of SRP by benthic algae, which is the direct way in which benthic algae affect the SRP release from sediments, is low in filtered water and increases with the SRP concentration. However, in the experiment, the increased uptake rate lasted for a short time(in one hour), and after that it returned to a low rate. Benthic algae make the DO concentration and the oxic layer thickness increased, which can indirectly reduce the SRP release from sediments. These findings indicate that benthic algae can reduce the SRP release from sediments in both direct and indirect ways. It seems that the indirect way also plays an important role in reducing the SRP release from sediments.