Removal characteristics of anionic metals by micellar-enhanced ultrafiltration

Surfactant-based separation of Fe(CN)(6)(3-) and CrO(4)(2-) using regenerated cellulose membrane was studied in order to assess the potential of micellar-enhanced ultrafiltration for the remediation of wastewater or groundwater polluted with ferriccyanide and chromate. In the ferriccyanide/octadecylamine acetate (ODA) and chromate/ODA systems, removal of ferriccyanide increased from 73 to 92% and to 98%, and that of chromate from 64 to 97% and to >99.9% as the molar ratio of ODA to ferriccyanide and to chromate increased from 1 to 2 and to 3, respectively. In the ferriccyanide/chromate/ODA system, while the removal of ferriccyanide increased from 62 to 72% and to 93%, the removal of chromate from 20 to 38% and to 68% as the molar ratio of ferriccyanide:chromate:ODA increased from 1:1:1 to 1:1:2 and to 1:1:4, respectively. With the molar ratio of 1:1:6, the removal was >99.9 and 98% for chromate and ferriccyanide, respectively. Ferriccyanide ions were more easily bound to ODA micelles because the binding power of ferriccyanide was greater than that of chromate.     

Removal of metals from aqueous solution and sea water by functionalized graphite nanoplatelets based electrodes

In the present wok, we have demonstrated the simultaneous removal of sodium and arsenic (pentavalent and trivalent) from aqueous solution using functionalized graphite nanoplatelets (f-GNP) based electrodes. In addition, these electrodes based water filter was used for multiple metals removal from sea water. Graphite nanoplatelets (GNP) were prepared by acid intercalation and thermal exfoliation. Functionalization of GNP was done by further acid treatment. Material was characterized by different characterization techniques. Performance of supercapacitor based water filter was analyzed for the removal of high concentration of arsenic (trivalent and pentavalent) and sodium as well as for desalination of sea water, using cyclic voltametry (CV) and inductive coupled plasma-optical emission spectroscopy (ICP-OES) techniques. Adsorption isotherms and kinetic characteristics were studied for the simultaneous removal of sodium and arsenic (both trivalent and pentavalent). Maximum adsorption capacities of 27, 29 and 32 mg/g for arsenate, arsenite and sodium were achieved in addition to good removal efficiency for sodium, magnesium, calcium and potassium from sea water.     

Removal of organic pollutants from produced water by batch adsorption treatment

This paper studied the adsorption of chemical oxygen demand (COD), oil and turbidity of the produced water (PW) which accompanies the production and reconnaissance of oil after treating utilizing powdered activated carbon (PAC), clinoptilolite natural zeolite (CNZ) and synthetic zeolite type X (XSZ). Moreover, the paper deals with the comparison of pollutant removal over different adsorbents. Adsorption was executed in a batch adsorption system. The effects of adsorbent dosage, time, pH, oil concentration and temperature were studied in order to find the best operating conditions. The adsorption isotherm models of Langmuir, Freundlich and Temkin were investigated. Using pseudo-first-order and pseudo-second-order kinetic models, the kinetics of oil sorption and the shift in COD content on PAC and CNZ were investigated. At a PAC adsorbent dose of 0.25 g/100 mL, maximum oil removal efficiencies (99.57, 95.87 and 99.84 percent), COD and total petroleum hydrocarbon (TPH) were identified. Moreover, when zeolite X was used at a concentration of 0.25 g/100 mL, the highest turbidity removal efficiency (99.97%) was achieved. It is not dissimilar to what you would get with PAC (99.65 percent). In comparison with zeolites, the findings showed that adsorption over PAC is the most powerful method for removing organic contaminants from PW. In addition, recycling of the consumed adsorbents was carried out in this study to see whether the adsorbents could be reused. Chemical and thermal treatment will effectively regenerate and reuse powdered activated carbon and zeolites that have been eaten.

Graphic abstract

     

Removal of some heavy metals by CKD leachate

In this study, Cu(II), Ni(II), and Zn(II) ions were precipitated from synthetic aqueous solutions as hydroxides by using CKD leachate. Precipitation tests were carried out batch wise in agitated flasks with single-metal solutions (each solution contained 100 mg/l of one of the three metals), and a multi-metal solution that contained 50 mg/l of each of the three elements. The results showed that high removal efficiencies, approaching 100%, of these heavy metals were attained and the leachate of the solid waste CKD, therefore, can be used for removing heavy metals from aqueous solutions.     

Removal of azobenzene from water by kaolinite

The use of natural kaolinite clay to remove azobenzene from aqueous solutions under different pHs, ionic strengths, initial solid mass used, and initial solution concentrations was investigated. Batch kinetic experiments showed that the adsorption of azobenzene onto kaolinite followed a pseudo-second-order kinetics with an initial rate of 7.2 mg/g-h and a rate constant of 0.19 g/mg-h. The equilibrium azobenzene adsorption on kaolinite was well described by the Langmuir and Freundlich isotherms with an adsorption capacity of 11 mg/g, or 60 mmol/kg, corresponding to a monolayer adsorption on the surface of kaolinite. Adsorption increased with decreases in solution pH and increases in solution ionic strength. The enthalpy change of adsorption was −38 kJ/mol, suggesting that both physical and chemical adsorption was responsible for the retention of azobenzene on kaolinite. The high affinity of azobenzene for siloxane and gibbsite surfaces was attributed to the attractive Coulombic and van der Waals’ forces between the surface and the planar structure of the organic molecule.     

Removal of anionic dyes from aqueous solutions by adsorption of chitosan-based semi-IPN hydrogel composites

Semi-IPN hydrogel composites for dye adsorption studies were prepared via photopolymerization of poly(ethylene glycol) (PEG) macromer and acrylamide (AAm) monomer in the presence of chitosan (CS). Swelling properties and kinetics of the hydrogel composites were investigated in aqueous solution and Acid Red 18 (AR 18) solution. The adsorption studies showed that the adsorption capacity for AR 18 increased with the increase of initial dye concentration and chitosan content in the hydrogels, but decreased with the increase of pH and ionic strength of dye solutions. Absorption kinetics of AR 18 followed pseudo second-order kinetic model at pH 2.0. The adsorption capacities for Acid Orange 7 (AO 7), Methyl Orange (MO) and Basic Violet 14 (BV 14) were also examined at pH 2.0, and the equilibrium adsorption data of AR 18, AO 7 and MO well fitted the Langmuir isotherm. The hydrogel composites could be potentially used as absorbents for anionic dye removal in wastewater treatment process.     

Removal of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans by three coagulants in simulated coagulation processes for drinking water treatment

Surface water from Guangzhou to which standard polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were added was treated by coagulation with ferric chloride (FC), polyaluminium chloride (PAC), and aluminium sulfate (AS) at optimum removal dosages for nature organic matter (NOM) to assess the polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) removal efficiencies. PCDD/Fs in suspended particulate matter (SPM) and treated water (TW) after coagulation were analysed. Low residual levels of PCDD/Fs were found in treated water after coagulation: 0.8% for FC, 0.9% for PAC, and 3.1% for AS. The removal efficiency calculated using these results was >99% for FC and PAC and 97-98% for AS. Most PCDD/Fs congeners could be removed by the three coagulation processes; the removal efficiency of FC and PAC was similar, and slightly higher than that of AS. The results also demonstrate that coagulation with FC preferentially removed tetra- and penta-substituted PCDD/Fs from raw water.     

Removal of an anionic dye by adsorption/precipitation processes using alkaline white mud

Alkaline white mud (AWM) has been investigated as a low-cost material for removal of an anionic dye, acid blue 80. The effects of contact time, initial pH of dye solution, AWM dosage, and the presence of inorganic anion sulphate or phosphate ion on removal of the dye were evaluated. The results show that AWM could be used as an effective material for removal of acid blue 80 in a pre or main process, particularly at high dye concentration (>300 mgL(-1)), reaching maximum removal efficiency of 95%. At low dye concentration, surface adsorption is mainly responsible for the dye removal, while chemical precipitation of the dye anions with soluble Ca(2+) and Mg(2+) may play a dominant role for the dye removal at high concentration, producing much less sludge than conventional adsorption method. Solution pH has only a limited effect on the dye removal due to high alkalinity and large pH buffer capacity of AWM suspension and thereby pH is not a limiting factor in pursuing high dye removal. The presence of SO(4)(2-) could reduce the dye removal by AWM only when SO(4)(2-) concentration is beyond 0.7 mmolL(-1). The dye removal may be significantly suppressed by the presence of phosphate with increasing concentration, and the reduction in the dye removal is much larger at high dye concentrations than at low ones.     

Removal of arsenic from water by zero-valent iron

Batch and column experiments were conducted to investigate the effect of dissolved oxygen (DO) and pH on arsenic removal with zero-valent iron [Fe(0)]. Arsenic removal was dramatically affected by the DO content and the pH of the solution. Under oxic conditions, arsenate [As(V)] removal by Fe(0) filings was faster than arsenite [As(III)]. Greater than 99.8% of the As(V) was removed whereas 82.6% of the As(III) was removed at pH 6 after 9h of mixing. When the solution was purged with nitrogen gas to remove DO, less than 10% of the As(III) and As(V) was removed. High DO content and low solution pH also increased the rate of iron corrosion. The removal of arsenic by Fe(0) was attributed to adsorption by iron hydroxides generated from the oxic corrosion of Fe(0). The column results indicated that a filtration system consisting of an iron column and a sand filter could be used for treatment of arsenic in drinking water.     

Removal of Pb by EDTA-washing in the presence of hydrophobic organic contaminants or anionic surfactant

Heavy metals and organic contaminants often coexist in contaminated soils, of which the remediation requires a combined or sequential use of surfactant and chelant in chemical-enhanced soil washing. This study investigated the Pb removal by EDTA-washing in the presence of the coexisting hydrophobic organic contaminants (marine diesel fuel, MDF) or anionic surfactant (sodium dodecyl sulfate, SDS). The results of batch experiments indicated a negative impact of MDF on Pb removal, whereas a positive or negative influence of SDS depending on the molar ratio of [EDTA]:[Pb]. The surface of MDF-contaminated soil was partially covered by free-phase MDF limiting the interaction between EDTA and sorbed Pb, especially at [EDTA]:[Pb]=1:1. Despite the ability of SDS itself for extracting Pb to some extent, probably through electrostatic interaction and dissolution of soil organic matter (SOM), the addition of SDS into EDTA solution only slightly enhanced Pb removal at [EDTA]:[Pb]=1:1 but inhibited at [EDTA]:[Pb]=2:1. This may be attributed to the SOM dissolution and the potential formation of ternary surface complexes, respectively. Along the same line of reasoning, it was not surprising that the optimal sequence for Pb removal was EDTA- followed by SDS-washing rather than the reverse sequence or simultaneous EDTA- and SDS-washing.     

Copper foams in water treatment technology: Removal of hexavalent chromium

Open-cell copper foams were prepared using a space holder technique and tested as filter-beds for the uptake and reduction of Cr(VI) in drinking water. The use of raw cane sugar as a space holder provides an environmentally friendly method for the production of foams with controllable porous network characteristics. Specifically, by applying a sugar volume of 70–80% with particle sizes in the range of 0.35–0.70 mm, it was possible to obtain final porosity of 65%, high structural stability, and enhanced interconnectivity of macropores required for the free flow of treated water. Smaller sugar particles ensure a smaller pore size and a higher specific surface area, favoring the interaction of water with the effective copper surface. Column tests indicated that a realistic filtering system using the Cu-foam can operate with complete Cr(VI) removal and minimum Cu leaching in the pH 7 ± 0.2 range, capturing chromium in the form of Cr(III) and Cr(VI) oxides. Chromium is homogeneously distributed and incorporated into the copper porous network allowing an almost unlimited lifetime of effective use compared to common adsorbents.     

Removal of trihalomethanes from drinking water by nanofiltration membranes

Chlorine reacts with the natural organic matter (NOM) in waters and forms disinfection by-products (DBP). Major of these by-products are trihalomethanes (THM) and haloacetic acids (HAA). They have been known to cause cancer and other toxic effects to human beings. This study determined the removal efficiencies of THM by nanofiltration (NF) techniques with NF200 and DS5 membrane. The rejection of this chlorination by-products was studied at various feed concentration by changing transmembrane pressure. Experimental results indicated that in general increasing operating pressure produces a higher flux but does not have a significant effect on THM rejection. On the other hand, increasing the feed concentration produces a little change in the overall flux and rejection capacity. NF200 membrane removed more THM than DS5 membrane. The higher removal efficiency of dibromochloromethane (DBCM) was attributed to brominating characteristics (higher molecular weight (MW) and molecular size). As a consequence, the results of this study suggest that the NF membrane process is one of the best available technologies for removing THM compounds.     

New sequential treatment for mature landfill leachate by cationic/anionic and anionic/cationic processes: optimization and comparative study

Two new applications for sequence treatment of mature (stabilized) landfill leachate, that is, cationic resin followed by anionic resin (cationic/anionic) and anionic resin followed by cationic resin (anionic/cationic), are employed and documented for the first time in the literature. Response surface methodology (RSM) concerning central composite design (CCD) is used to optimize each treatment process, as well as evaluate the individual and interactive effects of operational cationic resin dosage and anionic resin dosage on the effectiveness of each application in terms of color, chemical oxygen demand (COD), and NH(3)-N removal efficiency. A statistically significant model for color, COD, and NH(3)-N removal was obtained with high coefficient of determination values (R(2)>0.8). Under optimum operational conditions, the removal efficiency levels for color, COD, and NH(3)-N are 96.8%, 87.9%, and 93.8% via cationic/anionic sequence, and 91.6%, 72.3%, and 92.5% via anionic/cationic sequence, respectively. The experimental results and the model predictions agree well with each other.     

Removal of anionic contaminants by surfactant modified powdered activated carbon (SM-PAC) combined with ultrafiltration

A variety of inorganic contaminants may form toxic oxyanions in aqueous systems which pose significant hazard to human health and the ecosystem. In order to remove the oxyanions from aqueous stream effectively, surfactant-modified powdered activated carbon (SM-PAC) combined with ultrafiltration (UF) was proposed in this study. As the cationic surfactant, cetylpyridinium chloride (CPC), adsorbs on the surface of PAC, the zeta potential of PAC increases to +40 mV. Oxyanions such as chromate, ferricyanide and arsenate bind on SM-PAC by electrostatic interaction, then the contaminants bound with SM-PAC can be separated by UF membrane. 0.3 mM of chromate and ferricyanide are removed completely with 4.0 g/L of SM-PAC. In case of arsenate, the removal efficiency was lower than chromate and ferricyanide. It is considered that the competition occurs among anionic pollutants on the limited binding sites of SM-PAC and lower valence of arsenate results in the lower removal efficiency. High permeate flux is maintained during filtration. The spent SM-PAC was regenerated by the concentrated Cl⁻ solutions. NaCl solution whose molar Cl⁻ concentration is 1.4 times higher than the contaminants bound on SM-PAC was optimal for the regeneration. Regenerated SM-PAC exhibited similar adsorption capacity to fresh SM-PAC. SM-PAC combined with UF can effectively remove anionic contaminants. Moreover, the simple and efficient regeneration process is proposed.     

Removal of nitrate from water by electroreduction and electrocoagulation.

The aim of this work was to investigate the feasibility of the removal of nitrate from water by applying electrochemical methods such as electroreduction and electrocoagulation. In electroreduction, removal of nitrate to an allowable concentration has been accomplished at the pH range of 5-7 with energy consumption value of 1 x 10(-3) kWh g(-1). In electrocoagulation, an allowable concentration of nitrate has been achieved at the pH range of 9-11 with energy consumption value of 0.5 x 10(-4) kWh g(-1). Full removal of nitrate was also possible but with higher energy consumptions for these two methods.     

Removal of phosphate from polluted water by lanthanum doped vesuvianite

The adsorption capacities of vesuvianite and lanthanum doped vesuvianite were studied. The effects of different mass ratios of La/vesuvianite at different contact times, pHs, and temperatures on adsorption capacity were also studied. It was found that lanthanum doped vesuvianite exhibited higher adsorption capacity than undoped one due to the reaction of bounded lanthanum with phosphate. The adsorption capacity of lanthanum doped vesuvianite for phosphate removal increased with the increase of La/vesuvianite mass ratio. The Freundlich and Langmuir models were used to simulate the sorption equilibrium, and the results indicate that the Langmuir model had a better correlation with the experimental data than the Freundlich model did. When the initial phosphate concentration was 1 mg P/L, the adsorptive capacity rate would be 1.32 mg P/g lanthanum doped vesuvianite (La/vesuvianite mass ratio ≥0.14) at pH between 6 and 9 after 40 h. The concentrations of residual lanthanum ions in solution at different conditions were measured. Lanthanum doped vesuvianite was also used for the removal of phosphate in a polluted river water and it could be easily recycled once without losing its activity to a greater extent.     

Removal of nickel ions from water by multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were produced by chemical vapor decomposition using acetylene gas in the presence of Ferrocene catalyst at 800 degrees C, and then oxidized with concentrated nitric acid at 150 degrees C. Both (as-produced and oxidized) CNTs were characterized by TEM, Boehm titration, N2-BET and cation exchange capacity techniques. The adsorption capacity for nickel ions from aqueous solutions increased significantly onto the surface of the oxidized CNTs compared to that on the as-produced CNTs. The effects of adsorption time, solution pH and initial nickel ions concentrations on the adsorption uptake of Ni2+ for both the as-produced and oxidized CNTs were investigated at room temperature. Both Langmuir and Freundlich isotherm models match the experimental data very well. According to the Langmuir model the maximum nickel ions adsorption uptake onto the as-produced and oxidized CNTs were determined as 18.083 and 49.261 mg/g, respectively. Our results showed that CNTs can be used as an effective Ni2+ adsorbent due to the high adsorption capacity as well as the short adsorption time needed to achieve equilibrium.     

Removal of heavy metals using different polymer matrixes as support for bacterial immobilisation

Great attention is focused on the microbial treatment of metal contaminated environments. Three bacterial strains, 1C2, 1ZP4 and EC30, belonging to genera Cupriavidus, Sphingobacterium and Alcaligenes, respectively, showing high tolerance to Zn and Cd, up to concentrations of 1000ppm, were isolated from a contaminated area in Northern Portugal. Their contribution to Zn and Cd removal from aqueous streams using immobilised alginate, pectate and a synthetic cross-linked polymer was assessed. In most cases, matrices with immobilised bacteria showed better metal removal than the non-inoculated material alone. For the immobilisation with all the polymers, 1C2 was the strain that increased the removal of Zn the most, whereas EC30 was the most promising for Cd removal, especially when combined with the synthetic polymer with up to a ca. 11-fold increase in metal removal when compared to the polymer alone. Removal of individual metals from binary mixtures showed that there was differential immobilisation. There was greater removal of Cd than Zn (removals up to 40% higher than those showed for Zn). The results show that metal contaminated environments constitute a reservoir of microorganisms resistant/tolerant to heavy metals that have the capacity to be exploited in bioremediation strategies. Capsule immobilisation of bacteria in the naturally occurring alginate and pectate and in a synthetic cross-linked polymer increased the Zn and Cd removal abilities from single and binary contaminated waters; the applications with the synthetic polymer were the most promising for Cd and Zn removal in single and binary mixtures.