Removal of arsenic by bead cellulose loaded with iron oxyhydroxide from groundwater

A new adsorbent, bead cellulose loaded with iron oxyhydroxide (BCF), was prepared and applied for the adsorption and removal of arsenate and arsenite from aqueous systems. The continuing loading process of Fe in the cellulose beads was realized through hydrolization of ferric salts when alkaline solution was added dropwise. Spherical BCF had excellent mechanical and hydraulic properties. Akaganeite (beta-FeOOH), the reactive center of BCF that was stably loaded into the cellulose, had a high sensitivity to arsenite as well as arsenate. The maximum content of Fe in BCF reached 50% (w/w). In this study we investigated the adsorption behavior of arsenite and arsenate on BCF, including adsorption isotherms, adsorption kinetics, the influence of pH and competing anions on adsorption, and column experiments. The adsorption data accorded with both Freundlich and Langmuir isotherms. The adsorption capacity for arsenite and arsenate was 99.6 and 33.2 mg/g BCF at pH 7.0 with an Fe content of 220 mg/ mL. Kinetic data fitted well to the pseudo-second-order reaction model. Arsenate elimination was favored at acidic pH, whereas the adsorption of arsenite by BCF was found to be effective in a wide pH range of 5-11. Under the experimental conditions, the addition of sulfate had no effect on arsenic adsorption, whereas phosphate greatly influenced the elimination of both arsenite and aresenate. Silicate moderately decreased the adsorption of arsenite, but not arsenate. Both batch experiments and column experiments indicated that BCF had higher removal efficiency for arsenite than for arsenate. While the influent contaminant concentration was 500 microg/L in groundwater and the empty-bed contact time (EBCT) for arsenite and arsenate was 4.2 and 5.9 min, breakthrough empty-bed volumes at the WHO provisional guideline value of 10 microg/L were 2200 and 5000, respectively. BCF can be effectively regenerated when elution is done with 2 M NaOH solution. The column experiments for four cycles showed that stable and high removal efficiency of arsenic was sustained by BCF after regeneration.     

An investigation of the adsorption of C5-C12 hydrocarbons in the ppmv and ppbv ranges on Carbotrap B

The effects of concentration and temperature on the breakthrough volumes (Vb) of 23 volatile organic compounds on Carbotrap B have been determined using the frontal chromatography method. From the measured Vb, original isotherms have been produced and adsorption parameters based on the Langmuir, Freundlich, and Dubinin-Polyani adsorption models have been calculated. The calculated adsorption parameters describe the behavior of these VOC on Carbotrap B under the experimental conditions and are useful data for VOC sampling applications including adsorption modeling of pumped and diffusive sampling. Each of the adsorption models give similar results and are in good agreement with the experimental data in the ppmv concentration range. It will be shown that contrary to previous assumptions the Langmuir adsorption parameters obtained at ppmv concentrations cannot be used to predict Vb at ppbv concentrations and the calculated parameter mmax does not represent the maximum adsorbent capacity. The Freundlich and Dubinin-Polyani models are shown to be more successful in describing the adsorption behavior of the VOC at ppbv levels where Vb is independent of concentration. The isosteric heats of adsorption (-delta Hst) for some of the compounds have been determined using the Van't Hoff equation which can be used to predict the effect of temperature on Vb.     

Preparation of Lignin Based Anion Exchanger for Nitrate and Phosphate Removal

Tertiary amino alkali lignin (TA-AL) was successfully synthesized by a two-step approach;its application as an adsorbent for nitrate and phosphate ions in effluents was investigated.TA-AL was characterized by FT-IR,zeta potential,SEM,and elemental analysis.Kinetic and equilibrium adsorption isotherms were determined to investigate the adsorption capacity of TAAL.The results revealed that TA-AL had a very strong adsorption capacity towards anions;the value of pHPZC (PZC,point of zero charge) was about 9.2.The adsorption of nitrate and phosphate ions was related to effluent pH and initial anion concentration.The maximum absorption of nitrate and phosphate ions was about 26.9 and 18.4 mg/g when the initial concentration of the ions was 50 mg/L.The adsorption kinetics conformed to the pseudo-second-order kinetic equation,and the equilibrium data were suitably expressed by the Freundlich model.The regeneration studies confirmed that the lignin-based material was a promising adsorbent for nitrate and phosphate ions in water.     

枇杷叶多糖酶法提取工艺优化及其离子交换层析纯化

单因素试验和响应面试验得到酶法提取枇杷叶多糖最佳条件为提取时间2.95 h、提取温度41 ℃、酶用量15.6 mg/g,多糖提取率为8.03%。研究枇杷叶多糖在离子交换填料DEAE Sepharose CL-6B上的吸附行为,考察缓冲液pH值和离子强度对吸附等温线的影响。结果表明,在实验范围内,吸附平衡数据符合单分子层吸附的Langmuir方程,枇杷叶多糖在DEAE-Sepharose CL-6B上的吸附量随着缓冲液pH值的上升而增加,低离子强度的缓冲液有利于多糖的吸附。实验确定枇杷叶多糖离子交换柱层析进样条件为pH 8.0条件下,选取不含NaCl的缓冲液,通过离子交换柱层析后枇杷叶多糖被分为3 个组分,得率分别为32.66%、1.22%和3.12%。     

Effects of dissolved carbonate on arsenic adsorption and mobility

The effects of high aqueous carbonate concentrations on arsenic mobility and transport in the subsurface were studied in synthetic iron oxide-coated sand column experiments. Elevated aqueous carbonate concentrations in groundwater have been studied and linked, by some authors, to increased aqueous As concentrations in natural waters. This study found that increasing carbonate concentrations had relatively little effect on As(V) adsorption to the iron oxide-coated sand surface at pH 7. The adsorption of As(V) decreased marginally when the CO2(g) partial pressure increased from 10(-3.5) to 10(-1.8) atm, despite a 50-fold increase in total dissolved carbonate (0.072 to 3.58 mM). Increasing the CO2(g) partial pressure to 10(-10) atm resulted in only a slight decrease in As(V) adsorption and increase in mobility, despite a >300-fold increase in total dissolved carbonate (to 22.7 mM). When compared to phosphate, a known competitive anion, carbonate mobilized less adsorbed As(V) than was mobilized by phosphate, even when present in much higher concentrations than phosphate. This was also true for an experiment with lower pore water velocity and an experiment where As(II) was introduced instead of As(V). Our experiments conclude that while carbonate anions do compete with As for adsorption to iron oxide-coated sand, the competitive effect is relatively small with regard to the total concentration of adsorbed As and the potential competitive effects of phosphate.     

Removal of Cr(VI) from aqueous solutions by modified walnut shells

Walnut shell (WNS) (Juglans regia) has been utilised as an adsorbent for the removal of Cr(VI) ions from aqueous solutions after treatment with citric acid. The modification reaction variables, such as citric acid level (5-10 g), reaction time (0-24 h), and temperature (110-130 °C) were studied in batch experiments. The rate of adsorption was studied under a variety of conditions, including initial Cr(VI) concentration (0.1-1.0 mM), amount of adsorbent (0.02-0.20 g), pH (2-9), temperature and contact time (10-240 min). Adsorption of Cr(VI) is in all cases pH-dependent showing a maximum at equilibrium pH values between 2.0 and 3.0 for citric acid modified walnut shell (CA-WNS). The applicability of the Langmuir, Freundlich and D-R adsorption isotherms has been tested for the equilibrium. Maximum adsorption capacities of CA-WNS and untreated WNS under experimental conditions were 0.596 and 0.154 mmol/g for Cr(VI) ions, respectively.     

Observation of surface precipitation of arsenate on ferrihydrite

X-ray diffraction and Raman spectroscopy were used in this study to characterize arsenate phases in the arsenate-ferrihydrite sorption system. Evidence has been obtained for surface precipitation of ferric arsenate on synthetic ferrihydrite at acidic pH (3-5) underthe following experimental conditions: sorption density of As/Fe approximately 0.125-0.49 and arsenic equilibrium concentration of <0.02-440 mg/L. Surface precipitation occurred under apparently undersaturated (in the bulk solution phase) conditions, and probably involved initial uptake of arsenate by surface complexation followed by transition to ferric arsenate formation on the surface as indicated by XRD analysis. At basic pH (i.e., pH 8), however, no ferric arsenate was observed in arsenate-ferrihydrite samples at a sorption density of As/Fe approximately 0.125-0.30 and an arsenic equilibrium concentration of 2.0-1100 mg/ L. At pH 8, arsenate is sorbed on ferrihydrite predominantly via surface adsorption, and the XRD patterns resemble basically that of ferrihydrite.     

Individual and competitive adsorption of arsenate and phosphate to a high-surface-area iron oxide-based sorbent

Individual and competitive adsorption of arsenate and phosphate were studied on a high-surface-area Fe/Mn-(hydr)oxide sorbent with surface and bulk properties similar to those of two-line ferrihydrite. It has maximum adsorption densities of 0.42 micromol As m(-2) at neutral pH and 1.24 micromol As m(-2) at pH 3. A surface complexation model (SCM) that used the diffuse double layer model was developed that could simulate single and binary sorbate adsorption over pH 4-9. The predominant adsorbed arsenate and phosphate species were modeled as bidentate binuclear surface complexes at low pH and as monodentate complexes at high pH. The model initially overpredicted the inhibition of arsenate adsorption by the presence of phosphate. The overprediction was resolved by separating surface sites into two types: ones to which both arsenate and phosphate bind and a smaller number to which only phosphate binds. The modified model predicted the competitive adsorption of arsenate and phosphate over pH 4-9 at total As concentrations of 6.67 and 80.1 microM and a total P concentration of 129 and 323 microM. The model may be used to predict arsenic adsorption to the sorbent for a given water source based on solution chemistry.     

草鱼鱼鳞对对苯二酚的吸附特性及其机理

以草鱼鱼鳞为原料制备生物吸附剂,通过静态吸附实验研究其对水溶液中对苯二酚的吸附性能,系统地考察pH值、吸附剂用量、对苯二酚初始质量浓度、吸附时间、吸附温度对鱼鳞吸附效果的影响,并通过吸附动力学和热力学分析,探讨鱼鳞吸附对苯二酚的吸附机理。结果表明,鱼鳞吸附剂对对苯二酚具良好的吸附效果,其最佳吸附条件为：当温度为25℃、吸附剂用量0.5g/L、对苯二酚溶液初始质量浓度为100mg/L、溶液体系pH7、吸附时间8h时,鱼鳞吸附剂的吸附容量可达到76.71mg/g。吸附热力学和动力学分析表明,鱼鳞对对苯二酚的吸附是以物理吸附为主的多层吸附,准二级动力学模型可以较好地反映这种吸附动力学行为,Freundlich等温吸附方程能较好地描述其等温吸附行为。     

阳离子交换树脂静态吸附法特异性分离乳清中乳铁蛋白的关键技术

乳铁蛋白(lactoferrin,Lf)是一种对婴幼儿有重要生理功能的活性乳蛋白,掌握Lf特异性分离技术对打破国外技术垄断、降低成本、促进我国婴幼儿配方奶粉发展具有重要意义.该研究以乳清为原料,基于最大吸附量、吸附率、特异吸附为指标,对不同吸附剂做了筛选,探讨了工艺参数对吸附效果的影响及洗脱液离子浓度对洗脱效果的影响,...     

Influence of food matrix on inactivation of Bacillus cereus by combinations of nisin, pulsed electric field treatment, and carvacrol.

Carvacrol was used as a third preservative factor to enhance further the synergy between nisin and pulsed electric field (PEF) treatment against vegetative cells of Bacillus cereus. When applied simultaneously with nisin (0.04 microg/ml), carvacrol (0.5 mM) enhanced the synergy found between nisin and PEF treatment (16.7 kV/cm, 30 pulses) in potassium-N-2-hydroxyethylpiperazine-N-ethanesulfonic acid (HEPES) buffer. The influence of food ingredients on bactericidal activity was tested using skimmed milk that was diluted to 20% with sterile demineralized water. The efficacy of PEF treatment was not affected by the presence of proteins, and results found in HEPES buffer correlated well with results in milk (20%). Nisin showed less activity against B. cereus in milk. Carvacrol was not able to enhance the synergy between nisin and PEF treatment in milk, unless used in high concentrations (1.2 mM). This concentration in itself did not influence the viable count. Carvacrol did act synergistically with PEF treatment in milk, however not in HEPES buffer. This synergy was not influenced by proteins in milk, as 5% milk still allows synergy between carvacrol and PEF treatment to the same extent as 20% milk.     

Effects of dissolved carbonate on arsenate adsorption and surface speciation at the hematite--water interface

Effects of dissolved carbonate on arsenate [As(V)] reactivity and surface speciation at the hematite-water interface were studied as a function of pH and two different partial pressures of carbon dioxide gas [P(CO2) = 10(-3.5) atm and approximately 0; CO2-free argon (Ar)] using adsorption kinetics, pseudo-equilibrium adsorption/titration experiments, extended X-ray absorption fine structure spectroscopic (EXAFS) analyses, and surface complexation modeling. Different adsorbed carbonate concentrations, due to the two different atmospheric systems, resulted in an enhanced and/or suppressed extent of As(V) adsorption. As(V) adsorption kinetics [4 g L(-1), [As(V)]0 = 1.5 mM and I = 0.01 M NaCl] showed carbonate-enhanced As(V) uptake in the air-equilibrated systems at pH 4 and 6 and at pH 8 after 3 h of reaction. Suppressed As(V) adsorption was observed in the air-equilibrated system in the early stages of the reaction at pH 8. In the pseudo-equilibrium adsorption experiments [1 g L(-1), [As(V)]0 = 0.5 mM and I = 0.01 M NaCI], in which each pH value was held constant by a pH-stat apparatus, effects of dissolved carbonate on As(V) uptake were almost negligible at equilibrium, but titrant (0.1 M HCl) consumption was greater in the air-equilibrated systems (P(CO2) = 10(-3.5) atm) than in the CO2-free argon system at pH 4-7.75. The EXAFS analyses indicated that As(V) tetrahedral molecules were coordinated on iron octahedral via bidentate mononuclear ( 2.8 A) and bidentate binuclear (approximately equal to 3.3 A) bonding at pH 4.5-8 and loading levels of 0.46-3.10 microM m(-2). Using the results of the pseudo-equilibrium adsorption data and the XAS analyses, the pH-dependent As(V) adsorption under the P(CO2) = 10(-3.5) atm and the CO2-free argon system was modeled using surface complexation modeling, and the results are consistent with the formation of nonprotonated bidentate surface species at the hematite surfaces. The results also suggest that the acid titrant consumption was strongly affected by changes to electrical double-layer potentials caused by the adsorption of carbonate in the air-equilibrated system. Overall results suggest that the effects of dissolved carbonate on As(V) adsorption were influenced by the reaction conditions [e.g., available surface sites, initial As(V) concentrations, and reaction times]. Quantifying the effects of adsorbed carbonate may be important in predicting As(V) transport processes in groundwater, where iron oxide-coated aquifer materials are exposed to seasonally fluctuating partial pressures of CO2(g).     

Mechanisms of arsenate adsorption by highly-ordered nano-structured silicate media impregnated with metal oxides

The highly ordered mesoporous silica media, SBA-15, was synthesized and incorporated with iron, aluminum, and zinc oxides using an incipientwetness impregnation technique. Adsorption capacities and kinetics of metal-impregnated SBA-15 were compared with activated alumina which is widely used for arsenic removal. Media impregnated with 10% of aluminum by weight (designated to Al10SBA-15) had 1.9-2.7 times greater arsenate adsorption capacities in a wide range of initial arsenate concentrations and a 15 times greater initial sorption rate at pH 7.2 than activated alumina. By employing one- and two-site models, surface complexation modeling was conducted to investigate the relationship between the aluminum oxidation states in different media and adsorption behaviors shown by adsorption isotherms and kinetics since the oxidation phase of aluminum incorporated onto the surface of SBA-15 was Al-O, which has a lower oxidation state than activated alumina (Al2O3). Surface complexation modeling results for arsenate adsorption edges conducted with different pH indicated thatthe monodentate complex (SAsO(4)2-) was dominant in Al10SBA-15, while bidentate complexes (XHAsO4 and XAsO4-) were dominant in activated alumina at pH 7.2, respectively. In kinetic studies at pH 7.2 + 0.02, Al10SBA-15 had only a fast-rate step of initial adsorption, while activated alumina had fast- and slow-rate steps of arsenate adsorption. Therefore, it can be inferred that the monodentate arsenate complex, predominant in Al10SBA-15, leads to faster adsorption rates than bidentate arsenate complexes favored with activated alumina. An arsenate adsorption behavior and arsenate surface complexation were thought to be well explained by aluminum oxidation states and surface structural properties of media.     

Chromium(III) removal in tannery waste waters using Chinese Reed ( Miscanthus Sinensis), a fast growing plant

Dried Chinese Reed (Miscanthus sinensis) was investigated as adsorbent for the removal of Cr(III) from tannery wastewater. Batch mode adsorption studies were conducted using aqueous solutions of Cr(III). Parameters studied include Cr(III) concentration, agitation time, adsorbent dose and pH. Adsorption followed pseudo-second order kinetic model. Equilibrium adsorption data obeyed both Langmuir and Freundlich isotherms. Langmuir adsorption capacity was found to be 1.85 mg/g. Effects of pH on adsorption and desorption show that both ion exchange and chemisorption are involved in the adsorption process.     

TiO2-photocatalyzed As(II) oxidation in aqueous suspensions: reaction kinetics and effects of adsorption

Oxidation of arsenite, As(III), to arsenate, As(V), is required for the efficient removal of arsenic by many water treatment technologies. The photocatalyzed oxidation of As(III) on titanium dioxide, TiO2, offers an environmentally benign method for this unit operation. In this study, we explore the efficacy and mechanism of TiO2-photocatalyzed As(III) oxidation at circumneutral pH and over a range of As(III) concentrations approaching those typically encountered in water treatment systems. We focus on the effect of As adsorption on observed rates of photooxidation. Adsorption (in the dark) of both As(III) and As(V) on Degussa P25 TiO2 was examined at pH 6.3 over a range in dissolved arsenic concentrations, [As]diss, of 0.10-89 microM and 0.2 or 0.05 g L(-1) TiO2 for As(III) and As(V), respectively. Adsorption isotherms generally followed the Langmuir-Hinshelwood model with As(III) exhibiting an adsorption maxima of 32 micromol g(-1). As(V) adsorption did not reach a plateau under the experimental conditions examined; the maximum adsorbed concentration observed was 130 micromol g(-1). The extent of As(III) and As(V) adsorption observed at the beginning and end of the kinetic studies was consistent with that observed in the adsorption isotherms. Kinetic studies were performed in batch systems at pH 6.3 with 0.8-42 microM As(III) and 0.05 g L(-1) TiO2; complete oxidation of As(III) was observed within 10-60 min of irradiation at 365 nm. The observed effect of As(III) concentration on reaction kinetics was consistent with surface saturation at higher concentrations. Addition of phosphate at 0.5-10 microM had little effect on either As(III) sorption or its photooxidation rate but did inhibit adsorption of the product As(V). The selective use of hydroxyl radical quenchers and superoxide dismutase demonstrated that superoxide, O2-, plays a major role in the oxidation of As(III) to As(V).     

Methyl arsenic adsorption and desorption behavior on iron oxides

In virtually all Earth surface environments, methylated forms of arsenic can be found. Because of the widespread distribution and toxicity of methyl-arsenic compounds, their adsorption by soil minerals is of considerable interest. The objective of this study was to compare the adsorption and desorption behavior of methylarsonic acid (MMAsV), methylarsonous acid (MMAsIII), dimethylarsinic acid (DMAsV), dimethylarsinous acid (DMAsIII), arsenate (iAsV), and arsenite (iAsIII) on iron oxide minerals (goethite and 2-line ferrihydrite) by means of adsorption isotherms, adsorption envelopes, and desorption envelopes (using sulfate and phosphate as desorbing ligands). MMAsIII and DMAsIII were not appreciably retained by goethite or ferrihydrite within the pH range of 3 to 11, while iAsIII was strongly adsorbed to both iron oxides. MMAsV and iAsV were adsorbed in higher amounts than DMAsV on goethite and ferrihydrite at all pH values studied. MMAsV and iAsV exhibited high adsorption affinities on both goethite and ferrihydrite from pH 3 to 10, while DMAsV was adsorbed only at pH values below 8 by ferrihydrite and below 7 by goethite. All arsenic compounds were desorbed more efficiently by phosphate than sulfate. MMAsV, iAsV, and DMAsV each exhibited adsorption characteristics suggesting specific adsorption on both goethite and ferrihydrite. Increased methyl substitution resulted in both decreased adsorbed arsenic at low arsenic concentrations in solution and increased ease of arsenic release from the iron oxide surface.     

Influence of phosphate on bacterial adhesion onto iron oxyhydroxide in drinking water

The transport and storage of drinking water in water distribution systems can modify its initial composition and properties. The accumulation of bacteria on corroded pipes is prejudicial and may lower the microbiological quality of the water. Previous results have shown that when pipes are highly corroded, the addition of phosphate, used as an anticorrosion treatment, decreases the bacterial concentration in the water. We studied the possibility of using phosphate to reverse the surface charge of iron oxyhydroxide (FeOOH) to limit bacterial adhesion. Iron oxyhydroxide (IOH) particles and Escherichia coli SH 702 were used as models of corrosion products and bacterial contamination, respectively. Electrophoresis was used to characterize the initial surface charges of both types of particles and the modifications that occurred after the addition of phosphate anions. Flow cytometry and adhesion assays were used to build adsorption isotherms of bacteria on IOH versus (phosphated-) IOH. X-ray photoelectron spectroscopy permitted to determine the chemical composition of the E. coli envelope and to discuss on functional groups responsible for bacterial surface properties. In the present conditions, adding phosphate to water allowed a decrease of 75% of the bacteria adhering to IOH.     

Optimizing Assay and Extraction of Lipoxygenase in Wheat Germ

Using three-level seven-factor response surface methodology, wheat germ lipoxygenase (LPO) assay conditions were standardized. The important parameters were concentration of the substrate (linoleic acid), and surfactant (Tween 20), pH and temperature. The standardized LPO assay conditions for the 1 mL reaction volume were : 450 μM linoleic acid, 129 μM Tween 20, 175 mM ethanol, 1 mM EDTA, pH 6.2 (phosphate buffer), ionic strength 100 mM and 40°C. LPO extraction conditions were standardized by sequential variation of parameters. Optimum conditions were a single extraction of defatted wheat germ flour at 2–5°C with magnetic stirring of an extractant acetate buffer pH 4.5, ionic strength 100 mM, at buffer-to-solid ratio 10:l.     

Water Adsorption Isotherms and Storage Stability of Freeze-Dried Bovine Colostrum Powder

Moisture adsorption isotherms of freeze‐dried bovine colostrum powder were obtained using the gravimetric method at three temperatures (15, 25, and 35°C) in the water activity range of 0.11–0.86. The moisture adsorption isotherms of freeze‐dried bovine colostrum powder showed a sigmoid isotherm curve typical of the type II BET classification shape. The Guggenheim-Anderson-de Boer and Brunauer-Emmett-Teller models were recommended to fit experimental data well. The shelf life of freeze‐dried bovine colostrum powder packaged in aluminium-laminated polyethylene pouches was evaluated for 243 days, and the storage stability was investigated when stored at 25°C and 50% relative humidity. A slight increase in moisture content, a linear increase in color difference, and a slight decrease in IgG concentration were found within 60 days storage under the above-mentioned conditions.     

Sucrose, sodium dodecyl sulfate, urea, and 2-mercaptoethanol affect the thermal inactivation of R-phycoerythrin.

Thermal inactivation kinetics (D- and z-values) of the algal protein, R-phycoerythrin (R-PE), were studied under different buffer conditions (pH 4.0, 7.0, and 10.0) and concentrations of sucrose, sodium dodecyl sulfate (SDS), urea, and 2-mercaptoethanol (ME). R-PE solutions were heated in capillary tubes at temperatures between 40 and 90 degrees C depending on buffer conditions. Thermal inactivation parameters for R-PE, calculated on the basis of fluorescence loss, were modified by addition of chemicals. Overall, sucrose and ME had a thermostabilizing effect, while SDS and urea decreased thermal stability of R-PE. The z-values ranged from 5.9 degrees C in 50 mM NaCl, 20 mM glycine buffer, pH 10.0, to 37.8 degrees C in 60% sucrose, 50 mM NaCl, 20 mM phosphate buffer, pH 7.0. The z-values obtained for R-PE closely matched the z-values of some target microorganisms in food processes, suggesting R-PE might be used as a time-temperature integrator to verify thermal processing adequacy.