Advanced oxidation of natural organic matter using hydrogen peroxide and iron-coated pumice particles

The oxidative removal of natural organic matter (NOM) from waters using hydrogen peroxide and iron-coated pumice particles as heterogeneous catalysts was investigated. Two NOM sources were tested: humic acid solution and a natural source water. Iron coated pumice removed about half of the dissolved organic carbon (DOC) concentration at a dose of 3000 mg l(-1) in 24 h by adsorption only. Original pumice and peroxide dosed together provided UV absorbance reductions as high as 49%, mainly due to the presence of metal oxides including Al(2)O(3), Fe(2)O(3) and TiO(2) in the natural pumice, which are known to catalyze the decomposition of peroxide forming strong oxidants. Coating the original pumice particles with iron oxides significantly enhanced the removal of NOM with peroxide. A strong linear correlation was found between iron contents of coated pumices and UV absorbance reductions. Peroxide consumption also correlated with UV absorbance reduction. Control experiments proved the effective coating and the stability of iron oxide species bound on pumice surfaces. Results overall indicated that in addition to adsorptive removal of NOM by metal oxides on pumice surfaces, surface reactions between iron oxides and peroxide result in the formation of strong oxidants, probably like hydroxyl radicals, which further oxidize both adsorbed NOM and remaining NOM in solution, similar to those in Fenton-like reactions.     

Natural organic matter (NOM) in roof runoff and its impact on the Fe0 treatment system of dissolved metals

The present work investigates the impacts and mechanisms associated with natural organic matter (NOM) in the Fe0 treatment system of Cu2+ and Zn2+ under roof runoff conditions. The NOM in runoff waters was characterized using XAD-4/8 adsorption resins, copper complexation, acidic capacity and liquid chromatography with online carbon detection. Batch kinetic experiments and flow-through configurations were performed and the results of metal removal were elucidated taking into account the characteristics of NOM. Based on the findings, it is shown that NOM influences the removal of metals through several complex pathways. At an un-favored condition for adsorption of metals, i.e., on iron corrosion products, at pH相似文献   

Molecular size distribution of natural organic matter in raw and drinking waters.

The purpose of this study was to compare the molecular size distribution (MSD) of natural organic matter (NOM) in raw waters (RW) and drinking waters (DW), and to find out the differences between MSD after different water treatment processes. The MSD of NOM of 34 RW and DW of Finnish waterworks were determined with high-performance size-exclusion chromatography (HPSEC). Six distinct fractions were generally separated from water samples with the TSK G3000SW column, using sodium acetate at pH 7 as an eluent. Large and intermediate humic fractions were the most dominant fractions in surface waters (lakes and rivers), while in artificially recharged groundwaters and natural groundwaters intermediate and small fractions predominated. Water treatment processes removed the two largest fractions almost completely shifting the MSD towards smaller molecular size in DW. Granular activated carbon (GAC) filtration, ozonation, and their combination reduced all humic fractions compared to the conventional treatment. Humic fractions correlated with total organic carbon (TOC) content and chemical oxygen demand, this being especially true in RW. The results demonstrate that the HPSEC method can be applied for a qualitative and also for rough estimate quantitative analyzes of NOM directly from RW and DW samples without sample pretreatment.     

Adsorption/desorption properties of copper ions on the surface of iron-coated sand using BET and EDAX analyses

This study was conducted to develop a heating process for coating hydrated iron oxide on the sand surface to utilise the adsorbent properties of the coating and the filtration properties of the sand. BET and scanning electron microscope (SEM) analyses were used to investigate the surface properties of the coated layer. An energy dispersive X-ray (EDAX) technique of analysis was used for characterising metal adsorption sites on the iron-coated sand surface. The results indicated that the iron-coated sand had more micropores and higher specific surface area because of the attachment of iron oxide. Copper ions could penetrate into the micropores and mesopores of iron oxide on sand surface, and the regeneration of the iron-coated sand could be achieved by soaking with pH = 3.0 acid solution. Besides, the results of EDAX analysis showed that copper ions were chemisorbed on the surface of iron-coated sand. Results of the study developed an innovative technology for coating iron oxide on sand surface for the treatment of heavy metal in water.     

Iron oxide-loaded slag for arsenic removal from aqueous system

An effective adsorbent for arsenic removal from aqueous system was synthesized by loading iron(III) oxide on municipal solid waste incinerator melted slag. The loading was accomplished via chemical processes and thermal coating technique. The key point of the technique was the simultaneous generation of amorphous FeOOH sol and silica sol in-situ and eventually led to the formation of Fe-Si surface complexes which combined the iron oxide with the melted slag tightly. The surface morphology of the iron oxide-loaded slag was examined and the loading mechanisms were discussed in detail. The adsorbent was effective for both arsenate and arsenite removal and its removal capabilities for As(V) and As(III) were 2.5 and 3 times of those of FeOOH, respectively. Both affinity adsorption and chemical reactions contributed to arsenic removal. The effects of solution pH, contact time, arsenic concentration and adsorbent dosage on arsenic removal were examined and the optimum removal conditions were established. Furthermore, leaching of hazardous elements such as Cr(VI), As, Se, Cd and Pb from the adsorbent at a pH range of 2.5-12.5 was below the regulation values. Accordingly, it is believed that the iron oxide-loaded slag developed in this study is environmentally acceptable and industrially applicable for wastewater treatment.     

铁和铝氧化物涂层砂的过滤与吸附性能评价

总结性地对3种不同氧化物涂层砂和未涂层砂的表面特性、过滤和吸附性能进行了比较与分析,明确了适用范围。改性滤料的高温加热和碱性沉积两种制备方法中,涂铁宜选前者,涂铝宜用后者。涂层砂的比表面积增大,吸附容量增加,使石英砂表面电荷的带电性质改变,有利于水中杂质的去除。涂铁砂适合于除氟和除砷及除有机物;涂铝砂适合于除浊、除有机物和除锌。     

Removal of metal ions and humic acid from water by iron-coated filter media

Iron oxide is an excellent, regenerable adsorbent, and often controls free metals through adsorption reaction. The utilization of heating process for coating iron oxide on sand surface allowed the media to be used in a packed column. Iron-coated sand was investigated for adsorbing metal ions and natural organic matter from water by batch and column experiments. Chemical analysis (energy dispersive analysis of X-ray, EDAX) was used for characterizing the copper and lead adsorption sites on iron-coated sand. From the batch experiment results, the copper and lead ions could be removed simultaneously by the iron-coated sand in the competition adsorption system. The interaction between copper, lead ions and iron oxide on sand surface was primarily the chemical bonds. The maximum adsorption capacities of iron-coated sand for copper and lead were 0.259 mg Cu/g-sand and 1.211 mg Pb/g-sand, respectively. The presence of humic acid led to increase the adsorption of copper and lead. Results from column experiments indicated that the copper ions, lead ions and humic acid could be removed completely before the breakpoint. Consequently, the iron-coated sand may be applied for the adsorption/filtration of metal ions and natural organic matters from water.     

Effective adsorbent for arsenic removal: core/shell structural nano zero-valent iron/manganese oxide

Recently, nano zero-valent iron (nZVI) has emerged as an effective adsorbent for the removal of arsenic from aqueous solutions. However, its use in various applications has suffered from reactivity loss resulting in a decreased efficiency. Thus, the aim of this study was to develop an effective arsenic adsorbent as a core/shell structural nZVI/manganese oxide (or nZVI/Mn oxide) to minimize the reactivity loss of the nZVI. As the major result, the arsenic adsorption capacities of the nZVI/Mn oxide for As(V) and As(III) were approximately two and three times higher than that of the nZVI, respectively. In addition, the As(V) removal efficiency of the nZVI/Mn oxide was maintained through 4 cycles of regeneration whereas that of the nZVI was decreased significantly. The enhanced reactivity and reusability of the nZVI/Mn oxide can be successfully explained by the synergistic interaction of the nZVI core and manganese oxide shell, in which the manganese oxides participate in oxidation reactions with corroded Fe²⁺ and subsequently retard the release of aqueous iron providing additional surface sites for arsenic adsorption. In summary, this study reports the successful fabrication of a core/shell nZVI/Mn oxide as an effective adsorbent for the removal of arsenic from aqueous solutions.     

An overview of the methods used in the characterisation of natural organic matter (NOM) in relation to drinking water treatment

Natural organic matter (NOM) is found in all surface, ground and soil waters. During recent decades, reports worldwide show a continuing increase in the color and NOM of the surface water, which has an adverse affect on drinking water purification. For several practical and hygienic reasons, the presence of NOM is undesirable in drinking water. Various technologies have been proposed for NOM removal with varying degrees of success. The properties and amount of NOM, however, can significantly affect the process efficiency. In order to improve and optimise these processes, the characterisation and quantification of NOM at different purification and treatment processes stages is important. It is also important to be able to understand and predict the reactivity of NOM or its fractions in different steps of the treatment. Methods used in the characterisation of NOM include resin adsorption, size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) spectroscopy, and fluorescence spectroscopy. The amount of NOM in water has been predicted with parameters including UV-Vis, total organic carbon (TOC), and specific UV-absorbance (SUVA). Recently, methods by which NOM structures can be more precisely determined have been developed; pyrolysis gas chromatography-mass spectrometry (Py-GC-MS), multidimensional NMR techniques, and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). The present review focuses on the methods used for characterisation and quantification of NOM in relation to drinking water treatment.     

Characterizing dissolved organic matter and evaluating associated nanofiltration membrane fouling

Natural organic matter (NOM) characteristics were determined for three ground waters exhibiting different water quality conditions. The water quality of the three feed waters collected at various water table depths was characterized by XAD-8/-4 resin adsorption, high performance size exclusion chromatography with ultraviolet and dissolved organic carbon (DOC) detections, and Fourier transform infrared spectroscopy (FTIR) to determine NOM fractionation, molecular weight, and NOM functional groups, respectively. Systematic studies were conducted to identify potential NOM foulants in ground water for nanofiltration (NF) membrane fouling. The results show that the hydrophobic fraction of NOM in all of the samples was significantly high (71-93%) compared to the hydrophilic (1.7-22.6%) and transphilic (5.3-6.6%) fractions. However, insignificant flux-decline (less than 5%) was observed for the highest DOC (36.9 mg l(-1)) and hydrophobic NOM (93%) containing groundwater compared to the other lesser DOC and hydrophobic NOM containing ground waters. This is presumably due to either higher fractions of hydrophilic and transphilic NOM or inorganic interactions that may be major foulants. Based on FTIR, aromatic foulants were observed at 1662 cm(-1) (CO-NH2 or CO conjugated with aromatic rings) for the fouled NF membrane with the relatively low DOC source waters. The contact angle of the clean membrane (52 degrees ) decreased with fouling up to 42-47 degrees for fouled membranes with the various samples.     

Synthesis and characterisation of Pd-modified N-doped TiO2 for photocatalytic degradation of natural organic matter (NOM) fractions

Introduction

The removal of natural organic matter (NOM) from water is becoming increasingly important in order to prevent the formation of carcinogenic disinfection by-products. The inadequate removal of NOM has a bearing on the capacity of the other treatment processes to remove organic micro-pollutants or inorganic species that may be present in the water. New methods are therefore currently being sought to effectively characterise NOM and also to ensure that it is sufficiently removed from drinking water sources.

Methodology

Nitrogen- and palladium-co-doped TiO₂ was synthesised by a modified sol?Cgel method and evaluated for its photocatalytic degradation activity on NOM fractions under simulated solar radiation. The photocatalyst was characterised by FT-IR, Raman, XRD, DRUV?Cvis, SEM, TEM, EDS, XPS and TGA. FT-IR confirmed the presence of OH groups on thermally stable, nearly spherical anatase nanoparticles with an average diameter of 20?nm. PdO species appeared on the surface of the TiO₂ as small uniformly dispersed particles (2 to 3?nm). A red shift in the absorption edge compared to commercial anatase TiO₂ was confirmed by DRUV?Cvis. In order to gain a better insight into the response of NOM to photodegradation, the NOM was divided into three different fractions based on its chemical nature.

Results and discussion

Photodegradation efficiencies of 96, 38 and 15?% were realised for the hydrophobic, hydrophilic and transphilic NOM fractions, respectively. A reasonable mechanism was proposed to explain the photocatalytic degradation of the NOM fractions. The high photocatalytic activity could be attributed to the larger surface area, smaller crystalline size and synergistic effects of the co-dopants N and Pd in the TiO₂ crystal.     

Coagulation of colloidal material in surface waters: the role of natural organic matter

Organic matter has a great influence over the fate of inorganic colloids in surface waters. The chemical nature and structure of natural organic matter (NOM) will be an important factor in determining whether colloids will be stabilised or destabilised by NOM. Under environmentally relevant conditions, the ubiquitous fulvic acids are likely to be responsible for coating and imparting a negative charge to colloids. If the adsorbed polyelectrolyte coating produces an increase in absolute surface potential, it will act to stabilise colloids in the water column. On the other hand, colloidal organic carbon, especially chain-like structures, has been shown to be involved in the aggregation of inorganic colloids through the formation of bridges. It is highly probable that both adsorption and bridging flocculation are occurring simultaneously in the natural aquatic environment. The importance of each process depends directly on the nature and concentration of organic matter in the system and indirectly on the productivity of the lake, its hydrological pathways, temporal variations, temperature, etc. The present paper reports such results and emphasises the need to discriminate the different kinds of NOM.     

Effect of copper(II) on natural organic matter removal during drinking water coagulation using aluminum-based coagulants.

Coagulation has been proposed as a best available technology for controlling natural organic matter (NOM) during drinking water treatment. The presence of heavy metals such as copper(II) in source water, which may form copper-NOM complexes and/or interact with a coagulant, may pose a potential challenge on the coagulation of NOM. In this work, the effect of copper(II) on NOM removal by coagulation using alum or PAX-18 (a commercial polymerized aluminum chloride from Kemiron Inc., Bartow, Florida) was examined. The results show that the presence of 1 to 10 mg/L of copper(H) in the simulated waters improved the total organic carbon (TOC) removal by up to 25% for alum coagulation and by up to 22% for PAX-18 coagulation. The increased NOM removal with the presence of copper(II) in the waters can most likely be ascribed to the formation copper-NOM complexes that may be more adsorbable on aluminum precipitates and to the formation of copper(II) co-precipitates that may also adsorb NOM. The presence of 1 to 5 mg/L of copper(I) in the waters containing 3 mg/L NOM as carbon was reduced below the maximum contaminant level goal (1.3 mg/L as copper) using either coagulant. The results suggest that the presence of copper(H) in source water may not adversely affect the NOM removal by coagulation. A good linear correlation was observed between the TOC removal efficiency and the log-total moles of the precipitated metals, which include the metal ion from a coagulant and the divalent metal ion(s) in source water.     

Regeneration of iron for trichloroethylene reduction by Shewanella alga BrY

Zero valent iron (ZVI), the primary reactive material in several permeable reactive barriers, is often oxidized to ferrous or ferric iron, resulting in decreased reactivity with time. Iron reducing bacteria can reconvert the ferric iron to its ferrous form, prolonging the reduction of chlorinated organic contaminants. In this study, the reduction of Fe(II,III) oxide and Fe(III) oxide by a strain of iron reducing bacteria of the group Shewanella alga BrY(S. alga BrY) was observed in both aqueous and solid phases. S. alga BrY preferentially reduced dissolved ferric iron over the solid ferric iron. In the presence of iron oxide the Fe(II) ions reduced by S. alga BrY efficiently reduced trichloroethylene (TCE). On the other hand, Fe(II) produced by S. alga BrY covered the reactive surfaces of ZVI iron filings and inhibited the reduction of TCE by ZVI. The formation of precipitates on the iron oxide or Fe0 surface was confirmed by scanning electron microscopy. The results suggest that iron-reducing bacteria in the oxidized Fe0 barriers can enhance the removal rate of chlorinated organic compounds and influence on the long-term performance of Fe0 reactive barriers.     

Enhanced coagulation with polyaluminum chlorides: role of pH/alkalinity and speciation

Enhanced coagulation is considered to be among the best available techniques (BAT) for disinfection by-product (DBP) precursor removal in water treatment. Improving existing understanding requires further consideration of nuances of chemical speciation relative to source water chemistry. In this paper, the effect of alkalinity/pH and speciation on inorganic polymer flocculants, polyaluminum chlorides (PACls) for enhanced particle and natural organic matter (NOM) removal was investigated. Three kinds of well-characterized typical source waters in China with low, moderate, and high alkalinity were selected. Performance of coagulants is controlled not only by preformed species but also by those formed in situ. At neutral and basic pH values, PACls with higher basicity (ratio of OH(-)/Al), which have more stable preformed Alb (the rapid reacted species as in ferron assay), are more efficient for turbidity and NOM removal. At slightly acidic pH, PACls with lower basicity are more efficient since more Alb can be formed in situ. Optimal NOM removal was achieved at pH 5.5-6.5 for all PACls. Basicity, speciation, and dosage of coagulant should be optimized based on raw water alkalinity to enhance the removal efficiency of NOM.     

Manganese and iron oxide immobilized activated carbons precursor to dead biomasses in the remediation of cadmium-contaminated waters

The aim of the present investigation was to exploit the high specific surface area of activated carbons in immobilizing the manganese and iron oxides as to obtain a suitable, efficient and cost effective and environment benign wastewater treatment process in the remediation of cadmium-contaminated waters. The manganese and iron oxides were impregnated in situ onto the surface and pores of the activated carbons precursors to the rice hulls and areca nut wastes. The solids were characterized with the help of Fourier transform infrared spectroscopy and X-ray diffraction analytical data, and the BET specific surface area as obtained. The surface morphology of these solids was discussed with the help of scanning electron microscopic images. The activated carbon samples along with the manganese and iron immobilized activated carbons were further employed in the batch and column reactor operations in the remediation of cadmium-contaminated waters. The batch data showed that an increase in sorptive pH from 2.0 to 10.0 and concentration from 1.0 to 20 mg/L favoured the uptake of cadmium by these solids. Moreover, the 1,000 times increase in background electrolyte concentrations NaNO₃ caused an insignificant decrease in cadmium uptake by these solids, which inferred that sorbing ions/species were sorbed specifically and forming ‘inner-sphere’ complexes onto the solid surface. The concentration dependence data were utilized to model various adsorption isotherms and indicated that Freundlich adsorption isotherm was reasonably fitted well. The kinetic data was fitted well to the pseudo-second-order rate equations; hence, the equilibrium sorption capacity was estimated. Furthermore, the dynamic experiments carried out by the column experiments and the breakthrough data were fitted well to the non-linear Thomas equations; accordingly, the loading capacity of the column was estimated. Iron or manganese immobilized activated carbons showed relatively higher loading capacity compared to its precursor activated carbons hence showing its possible implication in the remediation processes. Moreover, among these modified ACs, IIAC showed higher removal capacity than the MIAC solid.     

5种铁氧化物去除As(V)性能的比较研究

为了从铁氧化物中筛选得到潜在经济有效的除砷材料,对5种铁氧化物去除As(V)的性能进行了比较研究。吸附实验结果表明,其吸附容量依次为施氏矿物四方纤铁矿水铁矿赤铁矿针铁矿,其吸附过程均符合准二级动力学,约24 h时吸附达到平衡。其中,pH=5时,施氏矿物的吸附容量达到83 mg/g。分别投加500 mg/L和300 mg/L的施氏矿物,可将含砷1.484 mg/L和0.850 mg/L、高TOC含量和高pH特征的模拟配水砷浓度降至0.01 mg/L以下。鉴于施氏矿物良好的吸附除砷性能,进一步通过SEM、FTIR和电位滴定对其表面特性进行了深入研究,结果显示,本研究中制备的施氏矿物存在结构性或表面吸附的SO42-,其(质子)表面位密度约为4.32个/nm2,表面质子化常数pK1为4.60,pK2为-8.98。     

Arsenic sorption by red mud-modified biochar produced from rice straw

Red mud-modified biochar (RM-BC) has been produced to be utilized as a novel adsorbent to remove As because it can effectively combine the beneficial features of red mud (rich metal oxide composition and porous structure) and biochar (large surface area and porous structure properties). SEM-EDS and XRD analyses demonstrated that red mud had loaded successfully on the surface of biochar. With the increasing of pH in solution, arsenate (As(V)) adsorption on RM-BC decreased while arsenite (As(III)) increased. Arsenate adsorption kinetics process on RM-BC fitted the pseudo-second-order model, while that of As(III) favored the Elovich model. All sorption isotherms produced superior fits with the Langmuir model. RM-BC exhibited improved As removal capabilities, with a maximum adsorption capacity (Q_max) for As(V) of 5923 μg g^?1, approximately ten times greater than that of the untreated BC (552.0 μg g^?1). Furthermore, it has been indicated that the adsorption of As(V) on RM-BC may be strongly associated with iron oxides (hematite and magnetite) and aluminum oxides (gibbsite) by X-ray absorption near-edge spectroscopy (XANES), which was possibly because of surface complexation and electrostatic interactions. RM-BC may be used as a valuable adsorbent for removing As in the environment due to the waste materials being relatively abundant.     

Sorption and reduction of tetrachloroethylene with zero valent iron and amphiphilic molecules

Effects of surfactants and natural organic matter (NOM) on the sorption and reduction of tetrachloroethylene (PCE) with zero valent iron (ZVI) were examined in this study. PCE reduction by ZVI depended on the ionic type of the surfactants. The removal of PCE and production of TCE with non-ionic Triton X-100 and cationic hexadecyltrimethyl-ammonium (HDTMA) at one-half and two times the critical micelle concentration (CMC) were 1.2-1.8 times higher than without surfactants because of the enhanced PCE partitioning and surface concentration by the sorbed surfactants. When anionic sodium dodecyl benzene sulfonate (SDDBS) at one-half and two times CMC and NOM at 20 mg l(-1) and 50 mg l(-1) concentrations were used, the removal of PCE doubled and TCE production decreased. In the presence of SDDBS, TCE production by ZVI was lower than with HDTMA and Triton X-100 while PCE removal was higher than with the other surfactants.     

Powdered activated carbon coupled with enhanced coagulation for natural organic matter removal and disinfection by-product control: application in a Western Australian water treatment plant

The removal of organic precursors of disinfection by-products (DBPs), i.e. natural organic matter (NOM), prior to disinfection and distribution is considered as the most effective approach to minimise the formation of DBPs. This study investigated the impact of the addition of powdered activated carbon (PAC) to an enhanced coagulation treatment process at an existing water treatment plant on the efficiency of NOM removal, the disinfection behaviour of the treated water, and the water quality in the distribution system. This is the first comprehensive assessment of the efficacy of plant-scale application of PAC combined with enhanced coagulation on an Australian source water. As a result of the PAC addition, the removal of NOM improved by 70%, which led to a significant reduction (80-95%) in the formation of DBPs. The water quality in the distribution system also improved, indicated by lower concentrations of DBPs in the distribution system and better maintenance of disinfectant residual at the extremities of the distribution system. The efficacy of the PAC treatment for NOM removal was shown to be a function of the characteristics of the NOM and the quality of the source water, as well as the PAC dose. PAC treatment did not have the capacity to remove bromide ion, resulting in the formation of more brominated DBPs. Since brominated DBPs have been found to be more toxic than their chlorinated analogues, their preferential formation upon PAC addition must be considered, especially in source waters containing high concentrations of bromide.