Application of iron-coated sand and manganese-coated sand on the treatment of both As(III) and As(V).

In this study, manganese-coated sand (MCS) and iron-coated sand (ICS) were applied in the oxidation of As(III) and adsorption of As(V), respectively. ICS and MCS were prepared by mixing FeCl3 and Mn(NO3)2, respectively, with Joomoonjin sand at 150 degrees C. In the batch adsorption isotherms, adsorption of As(III) and As(V) onto ICS followed a Langmuir type. ICS showed a greater capacity in the removal of As(V) than As(III) and also in the removal of As(V) compared with MCS. Three different configurations of ICS and MCS were used to investigate the oxidation of As(III) and adsorption of As(V) in a column. In the homogenised system, arsenic breakthrough was approximately two-times delayed compared with the separately packed systems. After breakthrough of arsenic, concentration of As(III) in the effluents was below 40 ppb for the entire reaction period in all configurations, and most arsenic was identified as As(V) owing to near complete conversion of As(III) to As(V) by MCS. The catalytic activity of MCS on the oxidation of As(III) was maintained up to 700 pore volumes, which corresponds to the treatment of at least 300 mg As(III) based on the 1 kg MCS. Compared with the homogenised column, the released Mn(II) concentration from two-staged and four-staged columns was great for the entire reaction period. In the case where the same amount of ICS and MCS was packed in a filtration system, the homogenised column was identified as a better configuration compared with the two-staged and four-staged columns when considering the arsenic breakthrough time as well as the released concentration of Fe(III) and Mn(II).     

涂铁砂过滤去除水中磷的研究

试验制备一种涂铁砂(IOCS)滤料用于对水中磷的去除,与石英砂相比IOCS表面粗糙,空隙多,比表面积大,且附有α-Fe_2O_3晶体,吸附能力增强。通过过滤试验研究了IOCS滤料在不同的试验条件下(pH、空床接触时间、进水磷浓度、滤床深度等)对水中磷的去除效果。结果表明:中性条件下磷的去除效果最佳,pH太高和太低都不利于磷的去除;中性条件下,当空床接触时间为13min,进水磷浓度为1.0 mg/L,滤床深度为50 cm时,去除效果较好,平均去除率可达82%;空床接触时间、进水磷浓度、滤床深度等是影响过滤运行周期的主要因素。     

Removal of toxic heavy metals by iron-coated starfish.

In this study, the applicability of calcined starfish (SF) and iron-coated SF (ICSF) as potential adsorbents for the treatment of wastewater containing heavy metal ions was evaluated. ICSF was prepared by mixing FeCl(3) solution previously adjusted to pH 7 approximately 9 with SF at 105 degrees C. From the dissolution test at pH 2, ICSF showed strong acid-proof properties. In the batch adsorption, Cu(II) adsorption onto ICSF was completed within 150 minutes, while 47% Cu(II) was removed with SF alone. This result clearly suggests that the coated Fe(III) serves additional adsorption sites, resulting in the enhanced removal of heavy metal ions. The removed fraction of both Cu(II) and Pb(II) increased with increasing solution pH and nearly complete removals of Pb(II) and Cu(II) were observed at around pH 6 and 8, respectively. From the adsorption isotherm of Cu(II) onto SF and ICSF at pH 3.0, the removed amount of Cu(II) by ICSF was greater than that by SF over the entire concentration range studied. In the column test, the breakthrough of Cu(II) in the ICSF column was greatly retarded compared to that in the SF column. Based on the drinking water regulations for Cu(II), SF and ICSF were able to remove 3400 and 8600 mg/kg of Cu(II) from the wastewater, respectively.     

Removal of arsenic from groundwater by arsenite-oxidizing bacteria

The presence of arsenic in groundwater has been of great public concern because of its high toxicity. For purification of arsenic-contaminated groundwater, bacterial oxidation of arsenite, As(III), with a chemical adsorption process was examined in this study. After As(III) oxidation to arsenate, As(V), arsenic is easily removable from contaminated groundwater because As(V) is more adsorptive to absorbents than As(III). By acclimation to As(III) of high concentrations, a mixed culture of heterotrophic bacteria with high As(III)-oxidizing activity was obtained from a soil sample that was free from contamination. With initial concentration up to 1,500 mg l(-1) As(III), the mixed culture showed high As(III)-oxidizing activity at pH values of 7-10 and at temperatures of 25-35 degrees C. The mixed culture contained several genera of heterotrophic As(III)-oxidizing and arsenic-tolerant bacteria: Haemophilus, Micrococcus, and Bacillus. Activated alumina was added to the basal salt medium containing 75 mg l(-1) As(III) before and after bacterial oxidation. Arsenic removal by activated alumina was greatly enhanced by bacterial oxidation of As(III) to As(V). The isotherms of As(III) and As(V) onto activated alumina verified that bacterial As(III) oxidation is a helpful pretreatment process for the conventional adsorption process for arsenic removal.     

Removal of methylene blue from aqueous solution using wine-processing waste sludge

Dye wastewaters usually contain toxins and high chroma, making them difficult to treat with biological methods. The adsorption process plays an important role in removing dyes from wastewaters. This study aimed to explore the methylene blue (MB) adsorption mechanism by wine-processing waste sludge (WPWS). The WPWS contains a high cation-exchange capacity (64.2 cmol(c) kg(-1)) and organic matter (52.8%). The parameters affecting MB adsorption included pH, initial concentration of MB, reaction temperature, particle size and dosage of WPWS. The WPWS adsorption isotherms of MB were only well described by Langmuir adsorption isotherm. The maximum adsorption capacity (Q(m)) of MB was 285.7 mg g(-1) at 25 °C. The activation energy determined by Arrhenius equation is 29.995 kJ mol(-1). Under steady-state reaction conditions, the Gibb free energy (ΔG°) ranged from -24.607 to -27.092 kJ mol(-1) and ΔH° was -8.926 kJ mol(-1), indicating that lower reaction temperature would favor MB adsorption. Therefore, MB adsorption by WPWS was a spontaneous, exothermic and physisorption reaction.     

Removal of Ni(II) from aqueous solution using Moringa oleifera seeds as a bioadsorbent

Metal contaminants are generally removed from effluents by chemical and physical processes which are often associated with disadvantages such as the use of toxic reagents, generation of toxic waste and high costs. Hence, new techniques have been developed, among them the study of natural adsorbents, for instance, the use of Moringa oleifera seeds. The potential of M. oleifera seeds for nickel removal in aqueous systems was investigated. The seeds utilized were obtained from plants grown in Uberlandia/Brazil. After being dried and pulverized, the seeds were treated with 0.1 mol/L NaOH. Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analyses were used for the characterization of the material. Using the optimized methodology (50 mL of 4.0 mg/L Ni(II), pH range of 4.0-6.0, agitation time of 5 min and adsorption mass of 2.0 g) more than 90% of Ni(II) could be removed from water samples. The sorption data were fitted satisfactorily by the Langmuir adsorption model. Evaluation applying the Langmuir equation gave the monolayer sorption capacity as 29.6 mg/g. The results indicate that this material could be employed in the extraction of nickel, considering its ease of use, low cost and environmental viability, which make it highly attractive for application in developing countries.     

Removal of contaminants and pathogens from secondary effluents using intermittent sand filters

Intermittent infiltration percolation of wastewater through unsaturated sand bed is an extensive treatment technique aimed at eliminating organic matter, oxidizing ammonium and removing pathogens. The main purpose of this study was to determine the depuration efficiencies of a sand filter to remove contaminants from secondary wastewater effluents. Elimination of pathogenic bacteria (total and faecal coliforms, streptococci) and their relationship with the filter depth were investigated. Results showed a high capacity of infiltration percolation process to treat secondary effluents. Total elimination of suspended solids was obtained. Mean removal rate of BOD(5) and COD was more than 97 and more than 81%, respectively. Other water quality parameters such as NH(4)-N, TKN and PO(4)-P showed significant reduction except NO(3)-N which increased significantly in the filtered water. Efficiency of pathogenic bacteria removal was shown to mainly depend on the filter depth. Average reductions of 2.35 log total coliforms, 2.47 log faecal coliforms and 2.11 log faecal streptococci were obtained. The experimental study has shown the influence of the temperature on the output purification of infiltration percolation process.     

Sorption of benzoic acid from aqueous solution by cetyltrimethylammonium bromide modified birnessite

Layered manganese oxide (birnessite) has been studied for its use as catalytic materials. The research presented in this study investigates the sorption of benzoic acid from water on synthesized cetyltrimethylammonium bromide modified birnessite (CTAB-birnessite). The synthesized CTAB-birnessite was characterized by X-ray powder diffraction (XRD). The experimental results of sorption kinetic were well fitted to the pseudo-second-order equation. The sorption isotherms were linear at different pH values, and it indicates a partition mechanism. Up to about 53% of the dissolved benzoic acid was sorbed by CTAB-birnessite; in contrast, only 16% of the dissolved benzoic acid was sorbed by birnessite. These results indicate that CTAB-birnessite can be a potential sorbent for benzoic acid removal.     

Removal of lead(II) and copper(II) from aqueous solution using foitite from Linshou mine in Hebei, China

Foitite from Linshou mine in China's Hebei province was investigated as an adsorbent to remove Pb(II) and Cu(II) from aqueous solution. The results showed that foitite can readily remove heavy metal ions from aqueous solution. The data shows that the metal uptake for Pb(II) increases rapidly, accounting for 74.47% when contact time was 2 min. In contrast to Pb(ll), there was a worse capability for adsorption of Cu(II). In the first 4 min, the metal uptake accounted for 34.7%. According to the analytical results obtained from X-ray diffraction, laser Raman spectrum, X-ray energy dispersive spectrometer, and Zeta potential, the removal mechanism of Pb(II) and Cu(II) by using foitite can be explained as following: firstly, the existence of an electrostatic field around foitite particles can attract heavy metal ions and consequently combine heavy metal ions with OH; secondly, heavy metal ions in the solution are exchanged with the Fe3+ and Al3+ in the foitite.     

Removal of ammonium from aqueous solutions using the residue obtained from struvite pyrogenation

This paper reports the results of laboratory studies on the removal of ammonium from aqueous solutions using struvite pyrogenation residues. A series of experiments were conducted to examine the effects of the pyrogenation temperature (90-210 °C) and time (0.5-4 h) on the ammonium release of struvite. In addition, the pyrolysate of struvite produced at different pyrogenation temperatures and times was recycled for ammonium removal from aqueous solutions. The experimental results indicated that the ammonium release ratio of struvite increased with an increase in the pyrogenation temperature and time, and the struvite pyrolysate used as magnesium and phosphate source for ammonium removal was produced at the optimal condition of pyrogenation temperature of 150 °C for 1 h. Furthermore, experimental results showed that the optimum pH and pyrolysate dosage for ammonium removal from 100 ml synthetic wastewater (1,350 mg ammonium/L) were at pH 9 and 2.4 g of struvite pyrolysate, respectively, and initial ammonium concentration played a significant role in the ammonium removal by the struvite pyrolysate. In order to further reduce the cost of struvite precipitation, the struvite pyrolysate was repeatedly used for four cycles. The results of economic analysis showed that recycling struvite for three process cycles should be reasonable for ammonium removal, with ammonium removal efficiencies of over 50% and a reduction of 40% in the removal cost per kg NH(4)(+).     

Sorption of Cr(III) ion from aqueous solution by two kinds of modified diatomite

Raw diatomite modified by microemulsion (DMM) and manganese oxide (MnD) were used for the removal of Cr(III) ions from aqueous solution. The characteristics and performance of these two types of modified diatomite on Cr(III) ion adsorption were compared. The results indicate that the Cr(III) ion adsorption capacities of diatomite were considerably improved after modifications by manganese oxide (MnO) and microemulsion. The surface area of MnD was increased because of the formation of MnO on the diatomite surface, and that of DMM was promoted owing to the existence of the hydrolyzed aromatic acid. Because of the stronger surface ionized function, the adsorption performance of Cr(III) ions in DMM was better than that in MnD. Within the experimental range of pH (i.e. 2.2-6.3), the Cr(III) ion removal of DMM (35-70%) was higher than that of MnD (33-59%) owing to the different electrostatic forces between the Cr(III) ion and the surface of the modified diatomite. The Cr(III) ion removal in MnD and DMM was improved with the increase of synthetic solution concentration in volumes from 0 to 2,500 mL.     

Removal of Cu(II) ions from aqueous solutions using N-carboxymethyl chitosan

N-carboxymethyl chitosan (NCMC) was synthesized by reacting chitosan with chloroacetic acid in water under triethylamine (Et(3)N) as catalyst. The chemical structures of NCMC were characterized by Fourier transform infrared (FT-IR) and hydrogen-1 nuclear magnetic resonance ((1)H-NMR) spectroscopy and confirmed that carboxymethylation occurred on the amino groups. Samples of NCMC were used for removal of Cu(II) from aqueous solution. The effects of degree of substitution of NCMC, initial pH value and adsorption kinetics on the adsorption were studied. Adsorption experiments showed that NCMC has a high adsorption speed and high adsorption capacity for remove Cu(II) from aqueous solution. The adsorption kinetics data were best fitted with the pseudo-second-order model. The experimental equilibrium data of Cu(II) on the NCMC were both fitted to the Langmuir model and Freundlich model, which revealed that the maximum capacity for monolayer saturation was 147.93 mg/g.     

Removal of copper(II) and cadmium(II) ions from aqueous solutions by biosorption onto pine cone

In this study, the removal of copper(II) and cadmium(II) ions from aqueous solutions by biosorption onto pine cone was studied. Variables that affect the biosorption process such as pH, biosorbent dosage, initial metal ion concentration, contact time and temperature of solution were optimized. Experimental data were fitted to Langmuir, Freundlich, Dubinin Radushkevich and Temkin isotherm models to investigate the equilibrium isotherms. Pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models were used to determine the biosorption mechanism. The thermodynamics of biosorption were studied for predicting the nature of biosorption. Experimental results showed that pine cone could be evaluated as an alternative precursor for removal of heavy metal ions from aqueous solutions, due to its high biosorption capacity, availability, and low cost.     

天然凹凸棒石对水中镉的吸附行为

通过静态实验探讨了天然凹凸棒石吸附水中镉Cd^2＋时的影响因素、动力学、等温式和热力学。结果表明．在实验条件下吸附90min后天然凹凸棒石对Cd^2＋的吸附量为6．07～13．15mg／g,吸附量随着温度或Cd^2＋的初始浓度的增加而增加,但天然凹凸棒石用量增加,吸附量却减少。在pH值为5—7时随着pH值的增加而增加。此外,天然凹凸棒石吸附Cd^2＋的速度较快,吸附60min后基本达到平衡。吸附动力学规律符合hgergren准二级反应模型,不同温度下的吸附等温式都与Freundlich方程符合很好。热力学分析表明,吸附过程吸热,吸附焓变△H和熵变,△S都为正值,吸附自由能变△G为负值。     

锰砂/石英砂滤池与纳滤膜组合工艺去除水中砷的研究

采用锰砂/石英砂滤池与纳滤膜组合工艺处理含砷水,考察锰砂/石英砂、纳滤膜(NF90、HL)、锰砂/石英砂滤池与纳滤膜组合工艺对水中砷的去除效果.结果表明,三价砷(As(Ⅲ))和五价砷(As(Ⅴ))经锰砂/石英砂过滤后能得到很好的去除,原水砷浓度250 μg/L,出水砷浓度小于50μg/L;纳滤膜对五价砷(As(Ⅴ))的去除能力很高,能达到90%以上,但是对三价砷(As(Ⅲ))的去除率不理想,为40%～60%;锰砂/石英砂复合滤池与纳滤膜组合工艺对水中砷有很好的去除效果,出水砷浓度均小于10μg/L,是理想的饮用水除砷方法.     

Preparation and characterization of CTAB-HACC bentonite and its ability to adsorb phenol from aqueous solution

A novel type of adsorbent was prepared by modifying bentonite with N-2-hydroxypropyl trimethyl ammonium chloride chitosan (HACC) with cetyl trimethylammonium bromide (CTAB). The adsorbent was named CTAB-HACC bentonite. Its characteristics were investigated using thermogravimetric, Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction. The adsorption of phenol onto CTAB-HACC bentonite was evaluated by changing various parameters, such as contact time, adsorbent dosage, initial pH of the solution, and temperature. The maximum adsorption was observed at pH 12. Adsorption of phenol on CTAB-HACC bentonite favored at lower temperature and established the equilibrium in 30 min. The adsorption efficiency reached 82.1%, and the adsorption capacity was 7.12 mg/g from the phenol solution with a concentration of 500 mg/L at pH 12.0 and 20 degrees C.     

Development of adsorbent for the simultaneous removal of organic and inorganic contaminants from aqueous solution

In this study, a modified adsorbent, alginate complex beads, was prepared and applied to the removal of mixed contaminants from wastewater. The alginate complex beads were generated by the immobilization of powdered activated carbon and synthetic zeolites onto alginate gel beads, which were then dried at 110 °C for 20 h until the diameter had been reduced to 1 mm. This dry technique increased the hardness of the adsorbent to assure its durability and application. The adsorption onto the alginate complex beads of organic and inorganic compounds, as target contaminants, was investigated by performing both equilibrium and kinetic batch experiments. From the adsorption isotherms, according to the Langmuir equation, the alginate complex bead was capable of effectively removing benzene, toluene, zinc and cadmium. From kinetic batch experiments, the removal efficiencies of benzene, toluene, zinc and cadmium were found to be 66.5, 92.4, 74.1 and 76.7%, respectively, for initial solution concentrations of 100 mg L(-1). The results indicated that the adsorbent developed in this study has the potential to be a promising material for the removal of mixed pollutants from industrial wastewater or contaminated groundwater.     

Potential application of manganese coated sand in the removal of Mn(II) from aqueous solutions.

The aim of this study was to explore the applicability of manganese coated sand (MCS) in the presence and absence of sodium hypochlorite for the removal of Mn(II) (2 mg/L) from aqueous solutions. Sand itself is widely used as a filter media for the treatment of wastewaters and it was reported that during the treatment, Mn(II), which is present in the wastewater, is to be deposited on the surface of sand in the form of manganese dioxide. The present investigation dealt with various MCS samples, prepared in the laboratory by various doses of Mn(II) (i.e. from 0.05 to 0.2 mol/L) and the samples were obtained from the pilot plant and naturally coated in the water treatment plant for the removal of Mn(II) in the batch and column studies. Moreover, it was realised that the role of hypochlorite is multifunctional as it not only enhances the uptake of Mn(II) on the surface of MCS through oxidation of Mn(II) into Mn(IV) and hence the formation of manganese dioxide, but it was also supposed to disinfect the bacteria or harmful pathogens from the waste/surface waters. The results obtained clearly inferred that various MCS samples used for the removal of Mn(II) from aqueous solutions showed comparable removal efficiency. However, the presence of sodium hypochlorite greatly enhanced the removal of Mn(II) as more than 80% Mn(II) was removed in the presence of sodium hypochlorite at around pH 6.5. Similarly, while comparing the column data it was again noted that the breakthrough points occurred after the 4,100 and 6,500 bed volumes, respectively, in the absence and in the presence of sodium hypochlorite (2 mg/L).     

Removal of C.I. Reactive Red 2 from aqueous solutions by chitin: an insight into kinetics, equilibrium, and thermodynamics

In this study, C.I. Reactive Red 2 (RR2) was removed from aqueous solutions by chitin. Exactly how the RR2 concentration, chitin dosage, pH, and temperature affected adsorption of RR2 by chitin was then determined. After reaction for 120 min, the amount of 10 and 20 mg/L RR2 absorbed onto chitin was 5.7 and 7.5 mg/g, respectively. The adsorption percentage increased from 56 to 94% when the chitin dosage was increased from 1.5 to 2.5 g/L. Experimental results indicated that the pseudo-second-order model best represents adsorption kinetics. Adsorption of RR2 increased as the temperature increased; however, it decreased with an increased pH. Experimental results further demonstrated that the Freundlich model is superior to the Langmuir model in fitting experimental isotherms. The ΔH° and ΔS° were 16.34 kJ/mol and 152.10 J/mol K, respectively. ΔH° suggested that adsorption of RR2 onto chitin was via physisorption.     

水上介质阻挡放电等离子体去除微囊藻毒素-LR的研究

研究水上介质阻挡放电等离子体对微囊藻毒素-LR(MC-LR)的去除及其反应动力学。在室温和常压下,考察了峰值电压、初始电导率、溶液初始浓度和pH对降解率影响。结果表明,水上介质阻挡放电等离子体降解MC-LR的过程均符合一级反应动力学。随着峰值电压的升高,MC-LR的降解率升高。高的溶液初始电导率和初始浓度不利于放电等离子体MC-LR的去除,反应过程中溶液的电导率增长速率与毒素降解速率呈现正相关性;pH在酸性和碱性条件下更有利于毒素的去除,反应20min后溶液pH均会下降到3左右,H+浓度直线上升;初始浓度为26.16μg/L的MC-LR经过100min的处理之后降解到0.23μg/L,去除率达到99.35%,低于国家《生活饮用水卫生标准》(GB5749～2006)限值1μg/L。