Effects of pH and competing anions on the speciation of arsenic in fixed ionic strength solutions by solid phase extraction cartridges

Anion exchange resins (AERs) separate As(V) and As(III) in solution by retaining As(V) and allowing As(III) to pass through. Anion exchange resins offer several advantages including cost, portability, and ease of use. The use of AERs for the instantaneous speciation of As minimizes the effects of preservatives on As species analysis. The aims of this study were to: (1) Examine the effects of pH and competing anions on the efficacy of solid phase extraction cartridges (SPECs) for speciation of As in a 0.01 molL(-1) NaNO(3) background electrolyte. (2) Identify optimal conditions (e.g. flow rates) for As speciation. (3) Calculate method detection limits (MDLs) from spiked background electrolyte and percent recoveries of As species from spiked extracts of mine wastes. The most effective SPEC retained As(V) through a range of environmentally relevant pH values (4-8). The mass loading capacity for As(V) was reduced in the background electrolyte (0.006 mg) compared with As(V) in deionized H(2)O (0.75 mg). Some retention (10-20%) of As(III) occurred on pre-wetted cartridges. Approximately 98% of spiked As(III) passed through dry cartridges. The recommended flow rate (0.5 mL min(-1)) was increased to 5 mL min(-1) without significant effect on As(V) retention. The presence of anions decreased the retention of As(V) with sulfate and phosphate having the greatest impact. MDLs were 0.004 mg L(-1) for both inorganic species. Spike recoveries in 0.01 M NaNO(3) mine waste extracts averaged 94% for As(III) and 107% for As(V).     

Effects of NOM properties on copper release from model solid phases

This study examined impacts of concentrations and properties of natural organic matter (NOM) on copper release from characteristic copper solid model phases such as tenorite CuO and malachite Cu₂(OH)₂CO₃. Unaltered Aldrich humic acid (AHA) and standard Suwannee River fulvic acid (SRFA) strongly increased copper release from the model phases but NOM alteration by chlorination or ozonation gradually suppressed or, at higher oxidant doses, eliminated these effects. The nature of NOM changes induced by chlorination and ozonation was examined using differential absorbance spectroscopy (DAS) and high-performance size-exclusion chromatography (HPSEC). The data of these methods show that NOM molecules with higher apparent molecular weight (AMW), higher aromaticities and contributions of protonation-active phenolic and carboxylic groups play a key role in adsorption and colloidal dispersion of the model solids. The data also show that metal release from model phases was well correlated with a number of spectroscopic parameters characterizing NOM properties, notably SUVA₂₅₄, spectral slopes of NOM absorbance, and differential absorbance at wavelength of 280 nm and 350 nm that is indicative of the contributions of carboxylic and phenolic functional groups. Changes of ζ-potential of the model solid phases were the strongest predictor of the enhancement of copper release especially in the system controlled by malachite. While effects of NOM on the ζ-potential of tenorite and malachite were prominent for unaltered NOM, its oxidation by chlorine and ozone was accompanied by a gradual decrease and ultimately disappearance of its surface activity.     

pH与Eh对郑州北郊水源地沉积物中砷溶出的影响

以郑州市北郊水源地富砷区域的地层沉积物(粗砂、细砂、粉土、黏土)为实验材料,研究了pH和氧化还原电位(Eh)对沉积物中砷溶出的影响规律,并分析了两个因素影响沉积物中砷溶出的原因.实验结果表明:碱性环境及还原环境有利于沉积物中砷的溶出.     

Evaluation of effect of leaching medium on the release of copper,chromium, and arsenic from treated wood

There is increasing public concern about environmental contamination from preservative treated wood due to release of toxic preservative components to the environment. Leaching of wood preservatives from treated wood in service can be affected by a number of factors such as wood and preservative treatment characteristics and properties of water and soil substrate in which treated wood is placed i.e. salinity, pH, and temperature. Laboratory leaching tests usually require distilled or deionized water for leaching procedure however treated wood is generally exposed to different types of water and soil conditions. This study evaluates the release of copper, chromium and arsenic elements from chromated copper arsenate (CCA)-treated wood exposed to either distilled water, tap water, sea water or humic acid. Leaching tests were conducted in laboratory conditions using wood blocks treated with CCA wood preservative at either low or high retention levels. Results showed that tap water resulted in less preservative release when compared to the other leaching media used in the study. Humic acid was the most effective medium causing more element leaching. The percentage of components leached was always higher in wood blocks treated at the high retention in comparison with the low retention level. Our results from the leaching tests can be important in developing more realistic standard leaching methods to evaluate preservative components to be released from treated wood.     

Effect of dry-wet cycles on leaching behavior of recovered soil collected from tsunami deposits containing geogenic arsenic

Geogenic contaminants, such as arsenic, are often found in soil recovered from coastal areas. These contaminants may leach out when the soil is used as embankment material. Moreover, the leaching of such contaminants might be influenced by environmental changes, such as dry-wet cycles, and higher environmental risks due to a larger amount of leaching are anticipated in some cases. In this study, therefore, soil recovered from tsunami deposits was subjected to dry-wet cycles under three different drying conditions to investigate how environmental changes affect the leaching behavior. To evaluate the physical and chemical changes in the soil surface, microscopic/spectroscopic studies were conducted. Batch leaching tests revealed that dry-wet cycles slightly alter the leaching behavior of most elements, such as Fe, Si, Na, Ca, etc. Arsenic leaching was seen to increase in certain dry-wet cycles before decreasing, and microscopic/spectroscopic confirmed that this increase was likely due to pyrite oxidation. These dry-wet cycles can disintegrate pyrite morphology and cause pyrite oxidation, leading to a more acidic leaching condition that accelerates arsenic leaching. After a certain oxidation procedure, the resulting ferric hydroxide may prevent the pyrite surfaces from further oxidation. The Fe oxides and hydroxides can also act as arsenic adsorbents, preventing the increase in arsenic concentration.     

Elucidating competitive adsorption mechanisms of atrazine and NOM using model compounds

Based on the relative adsorbability of natural organic matter (NOM) fractions with different molecular weights (MWs), two model compounds, poly(styrene sulfonate) (PSS) (nominal MW=1800 Dalton) and p-dichlorobenzene (DCB), were chosen to study the competitive effect of large and small NOM molecules on atrazine adsorption by two powdered activated carbons (PACs) with different pore size distributions. Both isotherm and kinetic tests of atrazine adsorption were conducted using fresh PAC and PAC preloaded with the model compounds. The model compounds were found to affect atrazine adsorption through two different mechanisms due to their size difference: direct competition for sites by p-DCB and pore constriction/blockage by PSS-1.8k. p-DCB was found to significantly reduce atrazine adsorption capacity but to have no effect on atrazine adsorption kinetics. In contrast, the effect of PSS-1.8k on atrazine adsorption capacity was very small. Furthermore, during simultaneous adsorption, PSS-1.8k had no effect on atrazine surface diffusion. However, preloading PAC with PSS-1.8k lowered the atrazine surface diffusion coefficient, D(s), by more than three orders of magnitude; D(s) decreased with increasing solid phase PSS-1.8k concentration. The pore size distribution of the PAC was found to play an important role in competitive adsorption. A high mesopore surface area could alleviate pore blockage significantly.     

Determination of arsenic leaching from glazed and non-glazed Turkish traditional earthenware

Glazed and non-glazed earthenware is traditionally and widely used in Turkey and most of the Mediterranean and the Middle East countries for cooking and conservation of foodstuff. Acid-leaching tests have been carried out to determine whether the use of glazed and non-glazed earthenware may constitute a human health hazard risk to the consumers. Earthenware was leached with 4% acetic acid and 1% citric acid solutions, and arsenic in the leachates was measured using hydride generation atomic absorption spectrometry. Arsenic concentrations in the leach solution of non-glazed potteries varied from 30.9 to 800 μg L^− 1, while the glazed potteries varied generally from below the limit of detection (0.5 μg L^− 1) to 30.6 μg L^− 1, but in one poorly glazed series it reached to 110 μg L^− 1. Therefore, the risk of arsenic poisoning by poorly glazed and non-glazed potteries is high enough to be of concern. It appears that this is the first study reporting arsenic release from earthenware into food.     

Determination of hydrophobicity of NOM by RP-HPLC,and the effect of pH and ionic strength

A reverse phase high performance liquid chromatography method for the determination of the hydrophobicity of natural organic matter (NOM) was developed by modification of an existing method based on elution with acetic acid/acetonitrile. The modified method separates the NOM into two well-defined groups according to their retention on a C18 column. The recovery was 101±11% for samples containing between 4 and 40 mg/L dissolved organic carbon (DOC). The method was tested for effects of ionic strength up to 0.8 eq. /L. Testing the method on eleven well-described NOM samples at pH 4.7 and 7.0 revealed the strong pH dependency of the hydrophobicity. The effect of pH on the hydrophobicity could be predicted from the proton binding properties of the NOM. Application of the method to NOM samples fractionated by HPSEC demonstrated considerable variations in hydrophobicity among the fractions, particularly at low pH.     

Effect of NOM on arsenic adsorption by TiO(2) in simulated As(III)-contaminated raw waters

The effect of natural organic matter (NOM) on arsenic adsorption by a commercial available TiO(2) (Degussa P25) in various simulated As(III)-contaminated raw waters was examined. Five types of NOM that represent different environmental origins were tested. Batch adsorption experiments were conducted under anaerobic conditions and in the absence of light. Either with or without the presence of NOM, the arsenic adsorption reached steady-state within 1h. The presence of 8 mg/L NOM as C in the simulated raw water, however, significantly reduced the amount of arsenic adsorbed at the steady-state. Without NOM, the arsenic adsorption increased with increasing solution pH within the pH range of 4.0-9.4. With four of the NOMs tested, the arsenic adsorption firstly increased with increasing pH and then decreased after the adsorption reached the maximum at pH 7.4-8.7. An appreciable amount of arsenate (As(V)) was detected in the filtrate after the TiO(2) adsorption in the simulated raw waters that contained NOM. The absolute amount of As(V) in the filtrate after TiO(2) adsorption was pH dependent: more As(V) was presented at pH>7 than that at pH<7. The arsenic adsorption in the simulated raw waters with and without NOM were modelled by both Langmuir and Frendlich adsorption equations, with Frendlich adsorption equation giving a better fit for the water without NOM and Langmuir adsorption equation giving a better fit for the waters with NOM. The modelling implies that NOM can occupy some available binding sites for arsenic adsorption on TiO(2) surface. This study suggests that in an As(III)-contaminated raw water, NOM can hinder the uptake of arsenic by TiO(2), but can facilitate the As(III) oxidation to As(V) at TiO(2) surface under alkaline conditions and in the absence of O(2) and light. TiO(2) thus can be used in situ to convert As(III) to the less toxic As(V) in NOM-rich groundwaters.     

Effect of NOM characteristics and membrane type on microfiltration performance

Efforts to understand and predict the role of different organic fractions in the fouling of low-pressure membranes are presented. Preliminary experiments with an experimental apparatus that incorporates automatic backwashing and filtration over several days has shown that microfiltration (MF) of the hydrophilic fractions leads to rapid flux decline and the formation of a cake or gel layer, while the hydrophobic fractions show a steady flux decline and no obvious formation of a gel or cake layer. The addition of calcium to the weakly hydrophobic acid (WHA) fraction led to the formation of a gel layer from associations between components of the WHA. The dominant foulants were found to be neutral and charged hydrophilic compounds, with hydrophobic and small pore size membranes being the most readily fouled. The findings suggest that surface analyses such as FTIR will preferentially identify hydrophilic compounds as the main foulants, as these components form a gel layer on the surface while the hydrophobic compounds adsorb within the membrane pores. Furthermore, coagulation pre-treatment is also likely to reduce fouling by reducing pore constriction rather than the formation of a gel layer, as coagulants remove the hydrophobic compounds to a large extent and very little of the hydrophilic neutral components.     

Effect of silica and pH on arsenic uptake by resin/iron oxide hybrid media

The recently imposed maximum contaminant level (MCL) of 10microg/L for arsenic has necessitated many water providers to implement efficient treatment systems to reduce the arsenic content in potable water supplies across the United States. A popular, cost-effective solution is to adsorb the arsenic onto hydrous iron oxide-based granular media. Hybrid media, consisting of hydrous iron oxides impregnated into a polymeric substrate in order to improve mechanical stability, have also been developed. The effective operational bed life of these adsorptive media is strongly dependent on the chemistry of the water being treated. High levels of silica combined with pH values greater than 8 have been shown to have a detrimental effect on the arsenic removal efficiency of all adsorptive media. Batch arsenate (arsenic(V)) adsorption experiments were performed to evaluate the effect of pH and silica on the static arsenic capacity of two iron oxide-based hybrid media, ArsenX(np) (a commercially available media) and npRio (a developmental media). From the data obtained, it was evident that the presence of increased levels of silica enhanced the detrimental effect of elevated pH on arsenic capacity, being most noticeable at pH 8 and above. In a solution containing 30ppm of SiO(2), a decrease in arsenic capacity as high as 71.8% was observed when the pH was increased from 7 to 9. Reducing the pH of the water prior to treatment may therefore be an economic option for improving media performance in drinking waters containing high concentrations of silica.     

Effect of NOM, turbidity and floc size on the PAC adsorption of MIB during alum coagulation

The effect of natural organic material (NOM) and turbidity on the powdered activated carbon (PAC) adsorption of the odour compound 2-methylisoborneol (MIB) was evaluated during alum coagulation. The character of the flocs, in terms of their size and fractal dimensions (Df), was used to interpret the observed adsorption behaviour of MIB during the coagulation process. As the alum dose was increased, the adsorption of MIB decreased. This was determined to be due to the size of the flocs, with larger flocs incorporating PAC into their structure, reducing the efficiency of mixing, and the bulk diffusion kinetics for the MIB molecule. The presence of turbidity also reduced MIB adsorption due to the formation of larger flocs. The character of NOM was found to have a greater influence on the adsorption of MIB than the floc structure.     

碳化对水泥制品中重金属元素溶出性能的影响研究

采用3种工业废弃物,配制水泥净浆试件,对比研究了标准养护和碳化作用条件下,水泥制品中重金属元素的溶出性能经时变化规律,分析了碳化作用对重金属溶出的影响机理。结果表明,重金属的溶出符合Fick扩散第二定律;溶出主要发生在前14 d,而后趋于平缓,21 d后溶出量极少;工业废弃物的重金属含量会显著影响其平均扩散系数和总溶出量。水泥基材料的高碱性环境、致密的孔隙结构以及稳定的水化产物形态是重金属元素稳定固化的重要保障,碳化由表及里地降低了材料的碱度和密实度,引起大部分水化产物分解,使得碳化作用后水泥试件的重金属溶出量和平均扩散系数增加。     

AFM study on the sorbed NOM and its fractions isolated from River Songhua

Natural organic matter (NOM) and its fractions from River Songhua were concentrated and fractionated with the reverse osmosis technology and XAD resin. With the purpose of exploring the adsorbed morphology of NOM and its fractions from a specific water source, the tapping-mode atomic force microscopy (TMAFM) was employed. The effect of solution properties (pH, Ca(2+)) on NOM microtopography was also verified. The results showed that NOM and its fractions displayed obviously diverse morphologies due to their different characteristics. The macromolecular compounds with large SUVA value were prone to adsorb on the mica surface. The particle-shaped NOM macromolecules were loosely adsorbed on the mica surface, and the molecular aggregation phenomena were proved to be ubiquitous in this experimental condition. With the increase of pH value, the surface coverage of mica decreased evidently. Spherical conformation with relatively smaller diameters was observed in the acidic condition compared with the neutral and basic condition. In the presence of 0.1 mol L(-1) NaCl, aggregation phenomena were observed in all pH conditions and obvious aggregates were presented with the addition of only 5 mmol L(-1) CaCl(2).     

Effect of NOM and biofilm on the removal of Cryptosporidium parvum oocysts in rapid filters

Laboratory experiments were performed to evaluate the effects of biofilm and natural organic matter (NOM) on removal of Cryptosporidium parvum oocysts from water by filtration. The bench-scale rapid filters consisted of 2.54 cm ID x 30.5 cm polycarbonate plastic columns packed with 0.55 mm spherical glass beads to a depth of 25 cm and a porosity of 40%. Calcium chloride (0.01 M) served as the coagulant in most of the experiments. The oocyst removal efficiency decreased from 51 +/- 6% for a clean bed to 23 +/- 3% for the biofilm-coated bed and to 14 +/- 1% in the presence of 5 ppm of NOM. The oocyst removal for an experiment with a combination of biofilm-coated filter media and NOM was similar to that for the experiment with NOM alone (15 +/- 1%). The zeta potential values for the oocysts pre-equilibrated with NOM were significantly more negative than those obtained for untreated oocysts. This suggests that NOM enhanced the electrostatic repulsion between the oocysts and the negatively charged glass beads. Fortunately, use of alum as coagulant at a dosage sufficient to neutralize the surface charge of the NOM-coated oocysts resulted in a high removal efficiency (73 +/- 6%). Pre-equilibration of the oocysts with NOM also increased the hydrophobicity of the oocysts, but this was deemed to have a negligible effect on deposition onto the glass beads. The results of these experiments suggest that water treatment facilities treating source waters with moderate organic matter concentrations and/or employing biologically active filters have a greater potential for oocyst breakthrough and proper coagulation is critical for effective removal of oocysts in the filters.     

Evaluating temperature effects on leaching behavior of geogenic arsenic and boron from crushed excavated rocks using shaking and nonshaking batch tests

The leaching behavior of arsenic and boron is evaluated in this work through two types of excavated rocks with geogenic contaminants under different temperatures. Excavated rocks with geogenic contaminants are expected to be used in embankments with appropriate countermeasures being taken against the risks brought about by geogenic contamination. The leaching behavior might change because of changes in the ground temperature. However, the effects of temperature on the leaching behavior of such rocks have not been well examined. Herein, batch leaching tests at temperatures between 5 and 60 °C were performed under shaking and nonshaking conditions. Mudstone and shale rock were crushed into particles smaller than 2 mm, which were required for the tests. The tests were carried out for durations ranging from 6 h to 15 days because changes in leaching kinetics also require careful evaluation. After conducting the nonshaking tests for 15 days at 40 °C, the mudstone sample leached arsenic and boron at concentrations of approximately 0.7 and 1.0 mg/L, respectively. The arsenic and boron concentrations were about 20 and 40% higher than those of the sample leached at a temperature of 20 °C. Elevated temperatures were seen to increase the leaching kinetics of the toxic elements. For the shale rock sample, the leaching rate for arsenic was 7.7 × 10^-2/h at 40 °C, which was about 2.5 times greater than the value at 30 °C. The nonshaking tests showed higher leaching amounts of arsenic and boron than the shaking tests, especially at elevated temperatures. As unrealistic estimations should be avoided, nonshaking tests are suggested. Moreover, nonshaking tests lasting longer than 6 h are necessary due to the relatively slow dissolution of minerals.     

松花江水中天然有机物及其分离组分的水处理性能和特性比较研究

采用反渗透和XAD大孔树脂提取分离技术进行NOM及其组分的浓缩和分离,结合一种商用腐殖酸(CHA)对几种有机物进行了臭氧氧化、混凝和吸附等水处理性能比较研究,采用多种表征技术,从特性比较分析的角度探讨了有机物特性与水处理性能之间的相互关系,并进一步考察了有机物的特性变化情况.结果表明,有机物的水处理性能与有机物的芳香性存在很强的相关性,依次以CHA＞HA＞FA=HyO=NOM＞HyI的顺序降低.然而,有机物的特性表征结果进一步证实,芳香性与分子质量之间缺乏必然的联系;E4/E6与芳香度SUVA和分子质量(Mw或Mn)之间缺乏联系;极性与有机物的芳香性存在良好的对应关系;官能团滴定结果与红外光谱分析结果具有一致性,因而多角度考察有机物的特性将有助于水处理工艺的优化.     

The influence of soluble organic matter from municipal solid waste compost on trace metal leaching in calcareous soils

The use of municipal solid waste (MSW) compost as fertilizer may cause increased leaching due to its high content of trace metals and thus pose a threat to groundwater quality. The effect of MSW compost application on trace metal leaching in calcareous soils has been studied in soil column experiments under laboratory conditions using three soils from the study area in the Gaza Strip and Israel. Higher levels of organic matter in solution (TOMS), nitrate, and the trace metals Cu, Ni and Zn were found in the leachates of a sandy soil and, to a lesser extent, a loamy soil, to which MSW compost had been applied at a rate of 65 Mg ha(-1) (dry weight basis). Nevertheless, the majority of water-soluble trace metal species from compost accumulated in the topsoil rather than washing out, with the exception of aqueous Ni species. Ni concentrations exceeded the maximum allowable limits for drinking water (in Germany: 50 microg l(-1)) at peak times in the leachates from sandy soil, while all other trace metals remained far below the corresponding limits. The highest absolute concentrations of trace metals were found for the leaching of Cu from compost-amended sandy soil (100 microg l(-1)). For Cd, Pb and Hg no evidence of downward movement was found in any assay. Gel filtration studies of the collected soil leachates showed that all trace metals encountered in the leachates existed mostly as organic complexes. In sandy soil most of the water-soluble organic matter added with the compost had leached from the rootzone after a year's equivalent of rainfall, while TOMS mobility was greatly reduced in the loamy soil. The makeup of the TOMS in the sandy soil and its metal-binding capacity was strongly influenced by compost-derived dissolved organic matter (DOM) as observed by FTIR spectrometry. Hence the vertical displacement of trace metals (Cu, Ni, Zn) in these calcareous soils seemed to result primarily from the presence of mobile metal-organic complexes in the soil solution after compost addition. Further studies are required to validate these findings in the field, especially to assess the risk of Cu and Ni leaching in sandy soil.     

嘉兴垃圾填埋场渗滤液的土柱淋滤实验研究

通过室内淋滤实验分析垃圾渗滤液-水-岩相互作用过程。实验发现Cl-的保守性是相对的,其中在粉砂土中Cl-存在吸附解吸现象,平衡浓度为4446mg/L时,分配系数Kd=0.18L/kg,而在壤土(亚粘土)中Cl-保持保守。SO42-和F-积极参与水岩相互作用,粉砂土和壤土对SO42-和F-均有较强的吸附作用。阴离子交换作用的结果使大量的NO 3-从粉砂土中解吸出来。     

Pore blockage effect of NOM on atrazine adsorption kinetics of PAC: the roles of PAC pore size distribution and NOM molecular weight

Natural organic matter (NOM) in natural water has been found to have negative effects on the adsorption of various trace organic compounds by activated carbon through two major mechanisms: direct competition for sites and pore blockage. In this study, the pore blockage effect of NOM on atrazine adsorption kinetics was investigated. Two types of powdered activated carbon (PAC) and three natural waters were tested to determine the roles of PAC pore size distribution and NOM molecular weight distribution in the pore blockage mechanism. When PAC was preloaded with natural water, the pore blockage effect of the NOM was found to cause a reduction of up to more than two orders of magnitude in the surface diffusion rate of atrazine compared to simultaneous adsorption of atrazine and NOM with fresh PAC. The surface diffusion coefficient of atrazine for preloaded PAC decreased with a decrease in PAC dose or an increase in NOM surface concentration. Because of the pore blockage effect of NOM, a 30% drop in atrazine removal was observed in a continuous flow PAC/microfiltration (MF) system after 7 days of contact compared to the removal predicted from the batch isotherm test. Large micropores and mesopores were found to play an important role in alleviating the effect of pore blockage. A PAC with a relatively large fraction of large micropore and mesopores was shown to suffer much less from the pore blockage effect compared with a PAC that had a much smaller fraction of large pores. Natural waters with different NOM molecular weight distribution caused different extent of pore blockage. The NOM molecules with molecular weight between 200 and 700 Dalton appeared to be responsible for the pore blockage effect.