Adsorption of natural organic matter from waters by iron coated pumice

Natural pumice particles were used as granular support media and coated with iron oxides to investigate their adsorptive natural organic matter (NOM) removal from waters. The impacts of natural pumice source, particle size fraction, pumice dose, pumice surface chemistry and specific surface area, and NOM source on the ultimate extent and rate of NOM removal were studied. All adsorption isotherm experiments were conducted employing the variable-dose completely mixed batch reactor bottle-point method. Iron oxide coating overwhelmed the surface electrical properties of the underlying pumice particles. Surface areas as high as 20.6m(2)g(-1) were achieved after iron coating of pumice samples, which are above than those of iron coated sand samples reported in the literature. For all particle size fractions, iron coating of natural pumices significantly increased their NOM uptakes both on an adsorbent mass- and surface area-basis. The smallest size fractions (<63 microm) of coated pumices generally exhibited the highest NOM uptakes. A strong linear correlation between the iron contents of coated pumices and their Freundlich affinity parameters (K(F)) indicated that the enhanced NOM uptake is due to iron oxides bound on pumice surfaces. Iron oxide coated pumice surfaces preferentially removed high UV-absorbing fractions of NOM, with UV absorbance reductions up to 90%. Control experiments indicated that iron oxide species bound on pumice surfaces are stable, and potential iron release to the solution is not a concern at pH values of typical natural waters. Based on high NOM adsorption capacities, iron oxide coated pumice may be a promising novel adsorbent in removing NOM from waters. Furthermore, due to preferential removal of high UV-absorbing NOM fractions, iron oxide coated pumice may also be effective in controlling the formation of disinfection by-products in drinking water treatment.     

An investigation into reservoir NOM reduction by UV photolysis and advanced oxidation processes

A comparison of four treatment technologies for reduction of natural organic matter (NOM) in a reservoir water was made. The work presented here is a laboratory based evaluation of NOM treatment by UV-C photolysis, UV/H(2)O(2), Fenton's reagent (FR) and photo-Fenton's reagent (PFR). The work investigated ways of reducing the organic load on water treatment works (WTWs) with a view to treating 'in-reservoir' or 'in-pipe' before the water reaches the WTW. The efficiency of each process in terms of NOM removal was determined by measuring UV absorbance at 254 nm (UV(254)) and dissolved organic carbon (DOC). In terms of DOC reduction PFR was the most effective (88% removal after 1 min) however there were interferences when measuring UV(254) which was reduced to a lesser extent (31% after 1 min). In the literature, pH 3 is reported to be the optimal pH for oxidation with FR but here the reduction of UV(254) and DOC was found to be insensitive to pH in the range 3-7. The treatment that was identified as the most effective in terms of NOM reduction and cost effectiveness was PFR.     

Pulsed discharge plasma induced Fenton-like reactions for the enhancement of the degradation of 4-chlorophenol in water

To sufficiently utilize chemically active species and enhance the degradation rate and removal efficiency of toxic and biorefractory organic pollutant para-chlorophenol (para-CP), the introductions of iron metal ions (Fe²⁺/Fe³⁺) into either pulsed discharge plasma (PDP) process or the PDP process with TiO₂ photo-catalyst were tentatively performed. The experimental results showed that under the same experimental condition, the degradation rate and removal efficiency of para-CP were greatly enhanced by the introduction of iron ions (Fe²⁺/Fe³⁺) into the PDP process. Moreover, when iron ions and TiO₂ were added together in the PDP process, the degradation rate and removal energy of para-CP further improved. The possible mechanism was discussed that the obvious promoting effects were attributed to ferrous ions via plasma induced Fenton-like reactions by UV light irradiation excited and hydrogen peroxide formed in pulsed electrical discharge, resulting in a larger amount of hydroxyl radicals produced from the residual hydrogen peroxide. In addition, the regeneration of ferric ions to ferrous ions facilitates the progress of plasma induced Fenton-like reactions by photo-catalytic reduction of UV light, photo-catalytic reduction on TiO₂ surface and electron transfer of quinone intermediates, i.e. 1,4-hydroquinone and 1,4-benzoquinone.     

Removal of NOM from drinking water: Fenton's and photo-Fenton's processes

The control of disinfection by-products during water treatment is primarily undertaken by reducing the levels of precursor species prior to chlorination. As many waters contain natural organic matter at levels of up to 15 mgl(-1) there is a need for a range of control methods to support conventional coagulation. Two such processes are the Fenton and photo-Fenton's processes and in this paper they are assessed for their potential to remove NOM from organic rich waters. The performance of both processes is shown to be depentent on pH, Fe: H2O2 ratio as well as Fe2+ dose. Under optimum conditions both processes achieved greater than 90% removal of DOC and UV254 absorbance. This removal lead to the trihalomethane formation potential of the water being reduced from 140 to below 10 microgl(-1), well below UK and US standards.     

Formation of hazardous by-products resulting from the irradiation of natural organic matter: comparison between UV and VUV irradiation

The use of ultraviolet (UV) or vacuum ultraviolet (VUV) photo-oxidation followed by biological treatment for the removal of natural organic matter (NOM) in drinking water is a potential water treatment technique under investigation. This paper reports on the trihalomethane formation potential (THMFP), the haloacetic acid formation potential (HAAFP), and formation of nitrite and peroxide following both UV and VUV irradiation of NOM prior to biological treatment. The total THMFP was found to decrease with increasing UV and VUV irradiation dose, although there was a linear increase in bromoform formation. Determination of the THMFP of NOM fractions obtained after irradiation, showed that the hydrophobic fraction was dominated by chlorinated species which accounted for the majority of the total THMFP, while bromoform was observed only in the hydrophilic fraction of NOM. VUV irradiation reduced the HAAFP with increasing dose, in contrast, UV irradiation had a limited effect on the overall HAAFP. Following UV or VUV irradiation, the chlorinated species accounted for the majority of HAAFP; however, significant formation of brominated haloacetic acid (HAA) was observed. The nitrate concentration of the untreated water directly influenced the concentration of nitrite produced as a consequence of UV and VUV irradiation. Hydrogen peroxide formation was greater during VUV irradiation than during UV irradiation. Samples exposed to various doses of UV or VUV irradiation (up to 138 J cm(-2)) were deemed non-cytotoxic (African green monkey kidney cells) and non-mutagenic (Ames test).     

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   

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.     

Studies of metal-binding sites in natural organic matter and their role in the generation of disinfection by-products using lanthanide ion probes

In this study, the complexation of Tb3+ with natural organic matter (NOM) was studied by the method of time-resolved fluorescence spectroscopy. In the presence of NOM, the excitation of Tb3+ was observed in a wide range of wavelengths, for which virtually no excitation of free Tb3+ took place. The pseudo-quantum yield spectra (excitation intensity normalized by corresponding light absorbance values) had a maximum at 282 nm. This indicated that the excitation of NOM-bound Tb3+ proceeds through energy transfer from aromatic groups in NOM. The concentration of the metal-binding sites (C(L)) was determined by titration with Tb3+ and was found to range from 0.21% to 0.83% of total moles of organic carbon. The actual number of the carbon atoms that comprise these functionalities was hypothesized to be at least seven times higher. The C(L) values were well correlated with the reactivity of NOM with chlorine quantified by total organic halogen formation potential and with the contribution of polyhydroxyaromatic moieties determined by pyrolysis-GC/MS method. The correlation of C(L) with the contributions of aromatic and carboxylic moieties in NOM determined by 13C NMR was poor. Based on the data, it was concluded that the metal binding functionalities in NOM are closely associated with halogen attack sites.     

Ligand exchange rate of metal-nom complexes by EDTA

Metal complexation by natural ligands is important for metal transport and distribution in surface and ground water. The goal of the work was to study the ligand exchange rate for two important metal ions in natural aquatic systems (Al, Fe) was determined using EDTA and natural organic matter (NOM) of humic type as ligands. After adding EDTA to a solution containing metal-NOM complexes, these complexes dissociated and metal-EDTA complexes were formed. Metal-NOM complexes were separated from metal-EDTA complexes with the help of size-exclusion chromatography and detected by on-line inductively coupled plasma-mass spectrometry (ICP-MS). Injecting the samples into the system over time after addition of EDTA allowed us to measure the rate of the exchange of NOM by EDTA. The experiments could be well described with a first-order rate law assuming that the dissociation of the metal-NOM complexes is the rate-determining step. The exchange rate of Fe was found to be faster than that of Al. This corresponds well with the exchange rate of water molecules from the coordination sphere of the metal ions, which is also faster for Fe than for Al. Furthermore, the UV and the fluorescence signal of the chromatograms were measured. The results indicate that no disaggregation of NOM molecules took place, although about 75-85% of the aggregate-forming metal ions exchanged NOM by EDTA in their coordination sphere. This suggests clearly the fundamental role of NOM in colloidal transport of metals and in their bioavailability.     

Catalytic degradation of chlorothalonil in water using bimetallic iron-based systems

Modified zero valent iron (MZVI) was used to study the transformation of a chlorothalonil (CLT) solution and the variation of the observed degradation rate of the reduction reactions. This was carried out when transition metals e.g. Pd, Cu and Co plated on the surface of micrometric iron particles (< 150 microm) were used as reducing catalytic agents for pesticide removal. Reactions were undertaken under both oxic and anoxic conditions in the presence and the absence of a phosphate buffer solution (PBS). Results of batch studies in nitrogen sparged solutions revealed that incomplete slow dechlorination merely occurred with zero valent iron (ZVI), however, complete rapid dechlorination reactions took place with MZVI especially Fe/Pd. Dechlorination was depicted by studying UV absorbance and MS spectra of CLT and all corresponding by-products. Typical blue shifts (deltalambda = 4-6 nm/chlorine atom) were observed at the same time as chlorine cluster isotopes disappeared. After the plating process, metal loading was controlled by analyzing the remaining metal in the solution by atomic absorption spectroscopy. Experiments showed that CLT degradation mechanism is faster in nitrogen sparged solutions in the absence of PBS. Time needed for complete removal of 2.08 +/- 0.19 microM CLT solution was about 2 h when experiments were conducted with ZVI (t1/2 = 15.0 min) and about 10 min when the reaction was carried out under the same conditions with Fe/Pd 1% (t1/2 = 1.0 min). Degradation rates for all bimetallic systems were determined showing that Pd is the more exciting catalytic transition metal followed by Cu and Co. Furthermore, MZVI method showed obvious advantage to traditional CLT treatment methods.     

Influences of redox transformation, metal complexation and aggregation of fulvic acid and humic acid on Cr(VI) and As(V) removal by zero-valent iron

This study investigated the removal kinetics and mechanisms of Cr(VI) and As(V) by Fe(0) in the presence of fulvic acid (FA) and humic acid (HA) by means of batch experiments. The focus was on the involvements of FA and HA in redox reactions, metal complexation, and iron corrosion product aggregation in the removal of Cr(VI) and As(V) removal by Fe(0). Synthetic groundwater was used as the background electrolyte to simulate typical groundwater. The results showed faster Cr(VI) removal in the presence of HA compared to FA. Fluorescence spectroscopy revealed that no redox reaction occurred in the FA and HA. The results of the speciation modeling indicate that the free Fe(II) concentration was higher in the presence of HA, resulting in a higher removal rate of Cr(VI). However, the removal of As(V) was inhibited in the HA solution. Speciation modeling showed that the concentration of dissolved metal-natural organic matter (metal-NOM) complexes significantly affected the aggregation of the iron corrosion products which in turn affected the removal of As(V). The aggregation was found to be induced by gel-bridging of metal-NOM with the iron corrosion products. The effects of metal-NOM on the aggregation of the iron corrosion products were further confirmed by TEM studies. Larger sizes of iron corrosion products were formed in the FA solution compared to HA solution. This study can shed light on understanding the relationships between the properties of NOM (especially the content of metal-binding sites) and the removal of Cr(VI) and As(V) by Fe(0).     

Enhanced chemical oxidation of aromatic hydrocarbons in soil systems

Fenton's destruction of benzene, toluene, ethylbenzene, and xylene (BTEX) was investigated in soil slurry batch reactors. The purpose of the investigation was to quantify the enhancement of oxidation rates and efficiency by varying process conditions such as iron catalyst (Fe(II) or Fe(III); 2, 5, and 10mM), hydrogen peroxide (H2O2; 30, 150, 300 mM), and metal chelating agents (l-ascorbic acid, gallic acid, or N-(2-hydroxyethyl)iminodiacetic acid). Rapid contaminant mass destruction (97% after 3h) occurred in the presence of 300 mM H2O2 and 10 mM Fe(III). An enhanced removal rate (>90% removal after 15 min and 95% removal after 3h) was also observed by combining Fe(III), N-(2-hydroxyethyl)iminodiacetic acid and 300 mM H2O2. The observed BTEX mass removal rate constants (3.6-7.8 x 10(-4)s(-1)) were compared to the estimated rate constants (4.1-10.1 x 10(-3)s(-1)). The influence of non-specific oxidants loss (by reaction with iron hydroxides and soil organic matter) was also explored.     

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.     

Comparative kinetic desorption of 60Co, 85Sr and 134Cs from a contaminated natural silica sand column: influence of varying physicochemical conditions and dissolved organic matter

In order to determine the mechanisms of the retention of 60Co, 85Sr and 134Cs in natural silica sand columns, desorption experiments were performed by changes of pH and ionic strength and by injection of natural organic matter (NOM). Injection of KCl (0.1 M) resulted in a high release of 60Co (60-100%) and 85Sr (72-100%) but a smaller release of 134Cs (31-66%). Only limited release of 60Co (66%) and 85Sr (71%) and no release of 134Cs were observed by injection of NOM. The different percentages of desorption were related to the chemical characteristics of the organic colloids previously retained in columns before the desorption step. The results evidenced different sorption processes on energetically heterogeneous surface sites. According to the initial conditions, the binding of the radionuclides to the solid phase resulted from weak and easily reversible sorption processes to strong association probably by inner sphere complexes. The rather weak release of 134Cs by KCl was attributed to the strong retention of 134Cs by clay coatings on the natural silica sand surfaces.     

Sorption and desorption hysteresis of organic contaminants by kerogen in a sandy aquifer material

Sorption and desorption hysteresis of 1,2-dichlorobenzene, 1,3,5-trichlorobenzene, naphthalene, and phenanthrene were investigated for the Borden aquifer material with total organic carbon of 0.021% and the isolated natural organic matter (NOM). The isolated NOM is a kerogen type of organic matter with relatively low maturation degree and contained many different types of organic matters including vitrinite particles. The modified Freundlich sorption capacities (logK^′_f and logK^′_foc) are very close for the sorption of the four solutes by the isolated NOM and the original sand, respectively. Isotherm non-linearity (n value) and hysteric behaviors are related to solute molecular properties (e.g. K_ow and molecular size). Kerogen encapsulated by inorganic matrices in the original aquifer may not be accessed fully by solutes. The larger the hydrophobic organic chemical (HOC) (hydrophobic organic contaminant) molecule is, the lower accessibility of the HOC to kerogen. This study disputes widely held hypothesis that sorption to mineral surfaces may play a major role in the overall sorption by low TOC (e.g. 0.1% by mass) geomaterials such as Borden sand. It also demonstrates the importance of the condensed NOM domain, even at very low contents, in the sorption and desorption hysteresis of HOCs in groundwater systems.     

Sorption of phenanthrene by nanosized alumina coated with sequentially extracted humic acids

Background, aim, and scope  

Sorption of hydrophobic organic compounds (HOCs) to natural organic matter (NOM) is an important process that affects the transport, transformation, bioavailability, and fate of HOCs in the environment. Manufactured nanoparticles (NPs) such as nano-oxides will inevitably enter the environment in the processes of their production, transfer, and use and could be coated by the ubiquitous NOM. Thus, sorption of HOCs to NOM in the environment could be affected by the NP interactions with NOM. Furthermore, the toxicity of nano-oxides could be increased due to the adsorbed HOCs. Therefore, sorption of phenanthrene by nano-Al₂O₃ coated with humic acid (HA) was examined in this study to explore the possible effect of nanoparticles (NPs) on the environmental behavior of HOCs and the potential environmental and health risks of NPs.     

Effect of pre-ozonation on optimized coagulation of a typical North-China source water

Although ozone is widely used as a pre-oxidant before coagulation in water treatment, the effect of pre-ozonation on optimized coagulation for removal of particle and natural organic matter (NOM) is still not fully understood. In this paper, pilot-scale investigation was conducted to examine the impact of pre-ozonation on coagulation for particle and NOM removal. Changes in the particle and NOM distributions were characterized by various methods, including laser light granularity system, particle counter, ultrafiltration, and resin absorbent fractionation. A novel composite flocculant–HPAC was compared with the traditional ferric chloride coagulant in terms of coagulation efficiency under the influence of pre-ozonation. Typical micro-polluted North China surface water was used for pilot coagulation tests. The results show that the effect of pre-ozonation on coagulation is associated with the dosage of ozone, coagulant type, and water contamination characteristics. For FeCl₃, pre-ozonation acts as a coagulation aid at low dosage (1.0 mg L⁻¹ O₃) for turbidity and UV₂₅₄ removal; while at higher dosage (2.0 mg L⁻¹ O₃), pre-ozonation is detrimental to UV₂₅₄ removal although it is still beneficial for turbidity removal. In the case of composite flocculant–HPAC, pre-ozonation demonstrates negligible influence on both turbidity and UV₂₅₄ removal. Ozone can simultaneously aggregate fine particles and break down large ones, making them more mineralized and easier to remove. NOM with intermediate molecular weight and hydrophobic neutral property increases at lower ozone dosage, favoring removal by coagulation. At higher ozone dosages, NOM becomes more hydrophilic and its molecular weight becomes smaller, decreasing NOM removal.     

臭氧光催化降解地下水中天然有机物的研究

在现场开展了中试规模的臭氧光催化降解天然有机物的研究.研究表明,对大分子天然有机物占很大比例且重碳酸盐含量较高的地下水,臭氧投加量10 mg/L和反应时间10 min条件下,TOC的去除率不到20%,但UV254和三卤甲烷生成潜力(THMFP)去除率分别达到近60%和33.5%.臭氧光催化与活性炭吸附相连,能显著提高UV254的THMFP的去除率,但TOC去除率并不明显高于单独活性炭吸附.臭氧光催化使大分子有机物转化为小分子有机物,后者在活性炭上的吸附性提高且生化性改善,可望在生物活性炭上更有效地去除.     

Atrazine removal by ozonation processes in surface waters

Atrazine (6-chloro-N-ethyl-N'-isopropyl-1,3,5-triazinedyl-2,4-diamine) was treated with ozone alone and in combination with hydrogen peroxide or UV radiation in three surface waters. Experiments were carried out in two bubble reactors operated continuously. Variables investigated were the ozone partial pressure, temperature, pH, mass flow ratio of oxidants fed: hydrogen peroxide and ozone and the type of oxidation including UV radiation alone. Residence time for the aqueous phase was kept at 10 min. Concentrations of some intermediates, including deethylatrazine, deisopropylatrazine and deethyldeisopropylatrazine, were also followed. The nature of water, specifically the alkalinity and pH were found to be important variables that affected atrazine (ATZ) removal. Surface waters with low alkalinity and high pH allowed the highest removal of ATZ to be reached. There was an optimum hydrogen peroxide to ozone mass flow ratio that resulted in the highest ATZ removal in each surface water treated. This optimum was above the theoretical stoichiometry of the process. Therefore, to reach the maximum removal of ATZ in a O3/H2O2 process, more hydrogen peroxide was needed in the surface waters treated than in ultrapure water under similar experimental conditions. In some cases, UV radiation alone resulted in the removal of ATZ higher than ozonation alone. This was likely due to the alkalinity of the surface water. Ozonation and UV radiation processes yield different amounts of hydrogen peroxide. Combined ozonations (O3/H2O2 and O3/UV) lead to ATZ removals higher than single ozonation or UV radiation but the formation of intermediates was higher.     

Contribution of free radicals to chlorophenols decomposition by several advanced oxidation processes

The chemical decomposition of aqueous solutions of various chlorophenols (4-chlorophenol (4-CP), 2,4-dichlorophenol (2-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP)), which are environmental priority pollutants, is studied by means of single oxidants (hydrogen peroxide, UV radiation, Fenton's reagent and ozone at pH 2 and 9), and by the Advanced Oxidation Processes (AOPs) constituted by combinations of these oxidants (UV/H2O2 UV/Fenton's reagent and O3/UV). For all these reactions the degradation rates are evaluated by determining their first-order rate constants and the half-life times. Ozone is more reactive with higher substituted CPs while OH* radicals react faster with those chlorophenols having lower number of chlorine atoms. The improvement in the decomposition levels reached by the combined processes, due to the generation of the very reactive hydroxyl radicals. in relation to the single oxidants is clearly demonstrated and evaluated by kinetic modeling.