Adsorption of Cd(II) by rhizosphere and non-rhizosphere soil originating from mulberry field under laboratory condition

In this study, the adsorption behavior of Cd ions by rhizosphere soil (RS) and non-rhizosphere soil (NS) originated from mulberry field was investigated. The Langmuir, Freundlich and the Dubinin–Radushkevich (D-R) equations were used to evaluate the type and efficiency of Cd adsorption. The RS was characterized by lower pH but the higher content of soil organic matter and cation exchange capacity (CEC) as compared to NS. Also, the maximum adsorption of Cd²⁺ for RS (5.87 mg/g) was slightly bigger than that for NS (5.36 mg/g). In Freundlich isotherm, the K_f of the adsorption of Cd²⁺ to surface of the RS components was higher than that of the NS, indicating stronger attraction between Cd²⁺ and components of the RS. According to the D-R model, the adsorption of Cd²⁺ by both soils was dominated by ion exchange phenomena. These results indicated that mulberry roots modified physical and chemical properties of the RS under field conditions, which also affected the Cd sorption efficiency by soil components during laboratory experiments. Current knowledge of the Cd²⁺ sorption processes in the rhizosphere of mulberry may be important if these trees are planted for use in phytoremediation of Cd contaminated soils.     

Biosorption of Cd(II) and Pb(II) onto brown seaweed, Lobophora variegata (Lamouroux): kinetic and equilibrium studies

The present work deals with the biosorption performance of raw and chemically modified biomass of the brown seaweed Lobophora variegata for removal of Cd(II) and Pb(II) from aqueous solution. The biosorption capacity was significantly altered by pH of the solution delineating that the higher the pH, the higher the Cd(II) and Pb(II) removal. Kinetic and isotherm experiments were carried out at the optimal pH 5.0. The metal removal rates were conspicuously rapid wherein 90% of the total sorption occurred within 90 min. Biomass treated with CaCl₂ demonstrated the highest potential for the sorption of the metal ions with the maximum uptake capacities i.e. 1.71 and 1.79 mmol g⁻¹ for Cd(II) and Pb(II), respectively. Kinetic data were satisfactorily manifested by a pseudo-second order chemical sorption process. The process mechanism consisting of both surface adsorption and pore diffusion was found to be complex. The sorption data have been analyzed and fitted to sorption isotherm of the Freundlich, Langmuir, and Redlich–Peterson models. The regression coefficient for both Langmuir and Redlich–Peterson isotherms were higher than those secured for Freundlich isotherm implying that the biosorption system is possibly monolayer coverage of the L. variegata surface by the cadmium and lead ions. FT-IR studies revealed that Cd(II) and Pb(II) binding to L. variegata occurred primarily through biomass carboxyl groups accompanied by momentous interactions of the biomass amino and amide groups. In this study, we have observed that L. variegata had maximum biosorption capacity for Cd(II) and Pb(II) reported so far for any marine algae. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Sorption of Cu(II) and Cd(II) by extracellular polymeric substances (EPS) from Aspergillus fumigatus

Sorption of Cu(II) and Cd(II) onto the extracellular polymeric substances (EPS) produced by Aspergillus fumigatus was investigated for the initial pH of the solution, EPS concentrations, contact time, NaCl concentration, initial metal ion concentration and the presence of other ions in the solution. The results showed that the adsorption of metal ions was significantly affected by pH, EPS concentrations, initial metal concentration, NaCl concentration and co-ions. The sorption of Cu(II) and Cd(II) increased with increasing pH and initial metal ion concentration but decreased with an increase in the NaCl concentration. The maximum sorption capacities of A. fumigatus EPS calculated from the Langmuir model were 40 mg g⁻¹ EPS and 85.5 mg g⁻¹ EPS for Cu(II) and Cd(II), respectively. The binary metal sorption experiments showed a selective metal binding affinity in the order of Cu(II) > Pb(II) > Cd(II). Both the Freundlich and Langmuir adsorption models described the sorption of Cu(II) and Cd(II) by the EPS of A. fumigatus adequately. Fourier transform infrared spectroscopy (FTIR) analysis revealed that carboxyl, amide and hydroxyl functional groups were mainly correlated with the sorption of Cu(II) and Cd(II). Energy dispersive X-ray (EDX) system analysis revealed that the ion-exchange was an important mechanism involved in the Cu(II) and Cd(II) sorption process taking place on EPS.     

Kinetics,Isotherms, and Thermodynamics of Hg(II) Biosorption onto Carica papaya

Carica papaya, a novel sorbent, was evaluated for sorption of Hg(II) from synthetic aqueous solutions using various pseudo-second order kinetic models as well as equilibrium sorption models. Batch kinetic and equilibrium experiments were carried out for the sorption of Hg(II) onto C. papaya at pH 6.5 and solid to liquid ratio (s/l) 1.0 g L^?1. The kinetic data were fitted to second order models of Sobkowsk and Czerwinski, Ritchie, Blanchard, Ho and McKay, whereas Langmuir, Freundlich, and Redlich-Peterson models were used for the equilibrium data. A comparative study on both linear and nonlinear regression showed that the Sobkowsk and Czerwinski and Ritchie's second order model were the same. Ho and McKay's pseudo-second order model fitted well to the experimental data when compared with the other second order kinetic expressions. Langmuir isotherm parameters obtained from the four Langmuir linear equations by using linear method were dissimilar, but were the same when nonlinear method was used. Additionally, various thermodynamic parameters, such as ΔG ⁰, ΔH ⁰, and ΔS ⁰, were calculated. The negative values of Gibbs free energy (ΔG ⁰) and ΔH ⁰ confirmed the intrinsic nature of biosorption process and exothermic, respectively. The negative value of ΔS ⁰ showed the decreased randomness at the solid-solution interface during biosorption.     

Regionalization of sorption capacities for arsenic and cadmium

To fulfill the purpose as a sink for trace elements, soils must not be overloaded with As and Cd. Therefore, it is necessary to get knowledge of the sorption capacities of soils on a regional scale. The determination of these sorption capacities for large areas is, however, impeded by the great expenditure of laboratory work involved. With data presented here retention capacities for cadmium and arsenic from routinely determined soil parameters are estimated. In batch experiments the sorption behaviour of 40 soils from the area of Freiberg/Saxony in Germany was examined. The obtained sorption isotherms from the laboratory were fitted to the Freundlich equation (S = k^*C^m). The two constants (k, m) of this equation were used for multiple linear regression to correlate the sorption capacity and the soil parameters, namely clay content, pH value, total organic carbon, and dithionite extractable Fe contents. Due to long lasting ore mining of Freiberg there exist high background levels in that area for the two surveyed elements As and Cd. Therefore, this study offers two different mathematical procedures to take these contaminations into account. Thus the experimental data were corrected before they were fitted to Freundlich and pedotransfer equations were determined. Using the transfer equation, parameter k and m for cadmium sorption could be estimated with statistical certainties of 91% and 61% (adjusted R²), respectively, whereas the predictability for the arsenic sorption is not practicable because achieved R₂ values are very low (17% and 7%). This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

Application of Two-and Three-Parameter Isotherm Models: Biosorption of Acid Red 88 onto Azolla microphylla

Biosorption potential of Azolla microphylla for acid red 88 from aqueous solution was investigated under laboratory conditions as a function of initial pH and temperature. The algal biomass exhibited the highest dye sorption capacity at optimum conditions of pH 3 and temperature 30°C. The experimental isotherms were analyzed using five two-parameter models (Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, and Flory-Huggins) and five three-parameter models (Redlich-Peterson, Sips, Khan, Radke-Prausnitz, and Toth). Three error analysis methods were used to evaluate the experimental data: correlation coefficient, residual root mean square error (RMSE), and chi-square test to find the best fitting isotherm. In particular, Langmuir (two-parameter) and Khan (three-parameter) models described the dye biosorption isotherm data well at all pH and temperature conditions examined.     

Bioremediation of cadmium-contaminated water systems using intact and alkaline-treated alga (Hydrodictyon reticulatum) naturally grown in an ecosystem

Cadmium can enter water, soil, and food chain in amounts harmful to human health by industrial wastes. The use of intact and NaOH-treated dried algal tissues (Hydrodictyon reticulatum), a major ecosystem bio-component, for Cd removal from aqueous solutions was characterized. Cadmium biosorption was found to be dependent on solution pH, bioadsorbent dose, the interaction between pH and dose, contact time, and initial Cd concentration. The experimental results indicated that the biosorption performance of alkaline-treated algal tissues was better than that of intact tissues. The maximum biosorption capacities were 7.40 and 12.74 mg g^?1 for intact and alkaline-treated bioadsorbents, respectively, at optimum operating conditions. Biosorption reaches equilibrium after 24 and 240 minutes of contact, respectively, for alkaline-treated and intact bioadsorbents. Cadmium biosorption was best fitted to Langmuir isotherm model (R² ≈ 0.99) and the kinetic study obeyed the pseudo-second-order kinetic model, which suggests chemisorption as the rate-limiting step in the biosorption process. Alkaline-treated algal tissues can be used as a new material of low-cost bioadsorbent for continuous flow rate treatment systems.     

Biosorption of heavy metals by lyophilized cells of <Emphasis Type="Italic">Pseudomonas stutzeri</Emphasis>

Biosorptive capacity of Pb(II), Cd(II) and Cu(II) by lyophilized cells of Pseudomonas stutzeri was investigated based on Langmuir and Freundlich isotherms. Biosorptive capacity for Pb(II), Cd(II) and Cu(II) decreased with an increase of metal concentration, reaching 142, 43.5 and 36.2 mg/g at initial concentration of 300 mg/l, respectively. Biosorption capacity for metal ions increased with increasing pH. The optimum pH for biosorption rate of Cd(II) and Cu(II) were 5.0, and 6.0 for Pb(II) biosorption. The experimental data showed a better fit with the Langmuir model over the Freundlich model for metal ions throughout the range of initial concentrations. The maximum sorptive capacity (q _max) obtained from the Langmuir equation for Pb(II), Cd(II) and Cu(II) were 153.3 (r ²  = 0.998), 43.86 (r ²  = 0.995), and 33.16 (r ²  = 0.997) for metal ions, respectively. The selectivity order for metal ions towards the biomass of P. stutzeri was Pb(II) > Cd(II) > Cu(II) for a given initial metal ions concentration. The interactions between heavy metals and functional groups on the cell wall surface of bacterial biomass were confirmed by FTIR analysis. The results of this study indicate the possible removal of heavy metals from the environment by using lyophilized cells of P. stutzeri.     

Sorption Behavior of Cesium in Two Greek Soils: Effects of Cs Initial Concentration,Clay Mineralogy,and Particle-size Fraction

The characteristics of Cs sorption behavior in two soils (soil 1 and soil 2) with nearly the same clay content and exhangeable K concentration, but with different clay mineralogy, were studied by the quantification of the distribution coefficient (k_d). It was observed that as the initial Cs concentration increased from 4 to 50 mg L^?1, the k_d values decreased in both soils, suggesting a progressive saturation of Cs available sorption sites. However, the presence of expansible 2:1 phyllosilicates minerals in the clay fraction of soil 2 maintained a high Cs sorption ability for this soil, even at high Cs concentrations. The experimental data were also fitted to the Freundlich isotherm and the results showed that parameters of the Freundlich equation could be used to estimate the degree of Cs sorption and the nature of the available sorption sites. For the studied soils, the k_f and the k_d values followed a similar trend and the n Freundlich constant values provided a reliable indicator for the soils’ clay mineralogy. The removal of the sand fraction enhanced Cs sorption in both soils and the absence of sorbed Cs ions on the quartz minerals, as observed by the SEM analysis, additionally supported the effect of particle-size fraction on Cs sorption.     

Sorption of Methylene Blue by an Oscillatoria sp.–Dominated Cyanobacterial Mat

The ability of an Oscillatoria sp.–dominated cyanobacterial mat in sorbing methylene blue (MB), a cationic dye, was investigated using the batch contact method. The sorption of MB onto the powdered biomass was not significantly influenced by initial pH (2–10) and temperature (5–45°C) of the solution. MB sorption occurred slowly, requiring 1–8 h for the establishment of equilibrium. A slow attainment of equilibrium seems to be related with the large size of MB ions. The isotherm data of MB sorption by the mat biomass could effectively fit to Langmuir and Freundlich models. The maximum MB sorption capacity (q _max) of the test biomass was 78.43 mg g^?1, which changed little with variation in biomass concentration. Moreover, the test biomass could efficiently sorb MB from solution in presence of Na⁺, K⁺, and Ca²⁺, which usually occur at high concentrations in natural waters, and also in presence of Cd²⁺. These particular characteristics together with pH and temperature independence of the sorption process make the mat biomass an ideal MB sorbent.     

Norfloxacin Sorption to Different Fractions in Sediments from Typical Water Systems in China

Sorption isotherms of Norfloxacin (NOF) to different fractions from six typical sediments in China were determined to compare the NOF sorption behavior and contribution of different fractions to total sorption. All sorption isotherms were nonlinear and fitted well with the Freundlich model. Sorption coefficients (K _f) by original sediments changed in larger magnitude, from 114 (mg/g)/(mg/L)ⁿ to 5271 (mg/g)/(mg/L)ⁿ, and black carbon with more aromatic carbon has more sorption capacity and nonlinearity. The sorption capacity K _f values were found to significantly correlate with SSA (specific surface area), OC (organic carbon), BC (black carbon), and TON (total organic nitrogen) (p < 0.05), but had no obvious relation with pH, CEC (cation exchange capacity), TOC/TON, and BC/TOC. The DOC removed, NaOH extracted, and 375°C heated fractions showed more nonlinear sorption than the original sediments, suggesting more heterogeneous sorption sites in these fractions. Among different sediment fractions, the 375°C heating fractions were responsible for >50% of the total NOF sorption over the whole concentration range. The contribution of DOC removed fractions to the total sorption was the highest at higher NOF concentration.     

Chromium(VI) sorption efficiency of acid-activated banana peel over organo-montmorillonite in aqueous solutions

In the present study, we examined sorption of chromate (Cr(VI)) to acid-activated banana peel (AABP) and organo-montmorillonite (O-mont) as a function of pH, initial Cr(VI) concentration at a sorbent dose of 4 g L^?1 and at 20 ± 1°C in aqueous solutions. In sorption edge experiments, maximum Cr(VI) removal was obtained at pH 3 after 2 hours by AABP and O-mont (88% and 69%). Sorption isotherm data showed that the sorption capacity of AABP was higher than O-mont (15.1 vs. 6.67 mg g^?1, respectively, at pH 4). Freundlich and Langmuir models provided the best fits to describe Cr(VI) sorption onto AABP (R² = 0.97) and O-mont (R² = 0.96). Fourier transform infrared spectroscopy elucidated that for AABP mainly the –OH, –COOH, –NH₂, and for O-mont intercalated amines and –OH surface functional groups were involved in Cr(VI) sorption. The scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX) analyses, although partly, indicate that the (wt. %) proportion of cations (e.g., Ca, Mg) in AABP decreased after Cr(VI) sorption. This may be due to ion exchange of chromite (Cr(III)) (produced from Cr(VI) reduction) with cationic elements in AABP. Also, Cr(VI) desorption (using phosphate solution) from AABP was lower (29%) than that from O-mont (51%) up to the third regeneration cycle. This bench scale comparative study highlights that the utilization of widely available and low-cost acid-activated biomaterials has a greater potential than organo-clays for Cr(VI) removal in aqueous media. However, future studies are warranted to precisely delineate different mechanisms of Cr(VI) sorption/reduction by acid-activated biomaterials and organo-clays.     

Biosorption of Cadmium by Live and Dead <Emphasis Type="Italic">Spirulina</Emphasis>: IR Spectroscopic,Kinetics, and SEM Studies

Cadmium is an important environmental pollutant and a potent toxicant to bacteria, algae, and fungi. Mechanisms of Cd⁺² toxicity and resistance are variable, depending on the organism. The present work reports the use of live and dead Spirulina sp. for sorption of Cd⁺². This investigation shows that this biomass takes up substantial amount of Cd⁺² ions. IR spectroscopic study, kinetics models, Langmuir & Freundlich adsorption isotherms, scanning electron microscopic analysis of Spirulina sp., and the Spirulina sp. treated with different metal ions have been employed to understand the sorption mechanism. Infrared spectra of live Spirulina treated with Cd⁺² ions for different lengths of time have been taken to understand the time dependency of metal interaction.     

LIVE AND DEAD SPIRULINA SP. TO REMOVE ARSENIC (V) FROM WATER

Arsenic (As)-contaminated water is a grave health hazard and its removal from water poses a great challenge. Conventional methods are associated with many shortcomings. Biosorption of arsenic using blue-green algae is an interesting alternative to conventional methods. In this article, the results of the biosorption of As(V) as AsO₄ ^{? 3} by live and dead Spirulina sp. are reported. The sorption of arsenic could be explained satisfactorily both by the Freundlich and the Langmuir isotherms. The maximum sorption capacities of live and dead Spirulina were estimated to be 525 and 402mg/g, respectively. These values are high in comparison with those reported for other arsenic sorbents. The sorption kinetics of arsenic by both live and dead Spirulina sp. could be well modeled by Lagergrens pseudosecond order-rate equation. Infrared spectra have been employed to understand how Spirulina sp. binds with arsenate. Scanning electron micrography and fluorescent microscopic images are used to discuss the extent of uptake. Preferential uptake of Cu(II), Ni(II), Cd(II), and AsO₄ ^?3 by live Spirulina sp. was investigated and explained with the help of rate constants for sorption.     

Impacts of Soil Organic Matter and Temperature on Sorption of Acetazolamide on Four Soils

Batch sorptions of acetazolamide (AZ) were conducted using four soils from China. Sorption of AZ was found to be impacted by OC, clay content, and soil pH, with higher k_d values for soils with higher clay content. The k_d values of SOM-removed soils are much lower than those of bulk soils. Sorption data were well fitted with a Freundlich model (r² > 0.99). Chelating with the metal ions on the surfaces of soil particles was probably involved. With pH increase, the electrostatic attraction between anionic AZ and positively charged soil surface may increase. The sorption capacity decreased when the temperature increased from 20 to 40°C, and the calculated thermodynamics parameters of ΔG₀, ΔH₀, and ΔS₀ indicated that the sorption was a non-spontaneous, physisorption, and exothermic process. Sorption coefficients (k_d) for the compound in soil were low (ranging from 0.42 to 1.19 L·kg^?1) and indicated that low level sorption of AZ with appreciable risk of ground water contamination.     

Effect of Soil Chemical and Physical Properties on Sorption and Desorption Behavior of Lead in Different Soils of India

Lead (Pb) is a non-biodegradable contaminant, present in the environment, especially near lead-based industrial sites, agricultural lands, and roadside soils. Bioavailability of Pb in the soil is controlled by the sorption and desorption behavior of Pb, which are further controlled by the soil chemical and physical properties. In this study, sorption and desorption amounts of Pb in soil were compared with soil physical (sand, silt, clay content) and chemical (pH; electrical conductivity, EC; percent organic carbon, (%OC); cation exchange capacity, CEC) properties. Twenty-six surface soils (0–5cm), expected to vary in physical and chemical properties, were collected from different parts of India and were treated with known concentration of Pb solution (40 μg/L). The amount of Pb sorbed and desorbed were measured and correlated with soil properties using simple linear regressions. Sorption was significantly (p ≤ 0.05) and positively correlated with pH, and %OC; desorption was significantly (p ≤ 0.05) negatively correlated with the same two factors. Stepwise multiple regressions were performed for better correlations. Predicted sorption and desorption amounts, based on multiple regression equations, showed reasonably good fit (R² = 0.79 and 0.83, respectively) with observed values. This regression model can be used for estimation of sorption and desorption amounts at contaminated sites.     

Biosequestering Potential of Spirulina platensis for Uranium

The uranium sequestering potential of Spirulina platensis was studied in batch mode, and its equilibrium was established in approximately 60 minutes. It had maximum sorption at pH 4.0 to 4.5. Equilibrium data is well represented by the Langmuir isotherm model followed by the Freundlich and Redlich-Peterson models. The interference of other cations and anions in solution was found to decrease sorption of the uranium, suggesting a competition for sorption sites on S. platensis. The desorption results showed that sodium citrate solution is effective, with 83% of uranium being recovered through nondestructive means.     

Influence of Bentonite Proportion in Natural Clay on Pb2+ ions Sorption: Response Surface Methodology,Kinetics and Equilibrium Studies

The influence of natural clay's bentonite proportion on Pb²⁺ sorption capacity was investigated using response surface methodology (RSM), kinetics and equilibrium studies. Experiments were conducted at different initial pH (3–7), bentonite to clay ratio (0–100%), initial Pb²⁺ ions concentration (20–120 mg/L) and sorbent dosage (0.2–1 g). Under the RSM study, data obtained from 27 experiments undertaken were found to fitted second-order polynomial model (R² = 0.998 and R²-predicted = 0.994). Analysis of variance showed that the Pb²⁺ sorption capacity was influenced according to the order; initial concentration> mass of adsorbent > initial pH > bentonite proportion. Optimal operating conditions were obtained at initial pH 5, 0.2 g sorbent dosage, 30% bentonite to clay ratio and 100 mg/L Pb²⁺ ion concentration. Regardless of the bentonite proportion, Pb²⁺ sorption kinetics followed pseudo-second-order associated with intra-particle diffusion. The sorption isotherm for the clay which was described by Freundlich yielded higher adsorption capacity (25 mg/g) while that of the bentonite was described by Langmuir model with lower maximum sorption capacity of 15 mg/g. These results suggest that sorption of the Pb²⁺ ions was not likely to significantly impact on the removal of Pb²⁺ ions during electrokinetic remediation process of clay having different proportion of bentonite.     

The Effect of Reservoirs on Phosphorus Concentration

The annual average degree of phosphorus retention (both TP and OP) in reservoirs was found to depend mainly on the theoretical retention time (RT). The phosphorus retention (RP) is shown for some reservoirs in Czech Republic to be well approximated (standard deviation = 10.9) with RP_(TP) = 74.7* (1-exp(-0.0255* RT)) (N = 38, 7 ≤ RT ≤ 604 days). The inclusion of 13 additional reservoirs for which data were assembled from literature resulted in an almost identical relationship: RP_(TP) = 76.1* (1-exp(-0.0282* RT)) (N = 51, range of RT nearly unchanged). The retention of soluble reactive phosphorus RP_(OP) studied on data from literature seems to be higher than that of TP. Statistical comparison with data for RP_(TP) of lakes has shown a significantly lower retention in lakes than in reservoirs for comparable RP, resulting in RP_(TP) = 66.0* (1-exp(-0.00419* RT)) (N = 59, 5.8 ≤ RT ≤ 260000 days). The differences between RP_(OP) and RP_(TP) and differentiation of lakes and reservoirs are discussed and a need for more thorough theoretical analysis stressed. Consequences for watershed management are summarized.