Dye removal from aqueous solution by adsorption on treated sawdust

Formaldehyde treated and sulphuric acid treated saw dusts were used to adsorb malachite green at varying dye concentration, adsorbent dose, pH and agitation time. Similar experiments were conducted with laboratory grade activated carbon to compare the results. The adsorption efficiency of sulphuric acid treated sawdust (SD) was higher than formaldehyde treated SD. The adsorption followed first order rate expression and Lagergren equation. An initial pH in the range of 6-9 was favorable for the dye removal by both the adsorbents. Dilute solutions were effectively decolorized by the adsorbents. It is proposed that in batch or stirred tank reactors, both adsorbents can be an attractive option for dye adsorption.     

Adsorption of Cr(VI) on activated rice husk carbon and activated alumina

The possible use of activated rice husk and activated alumina as the adsorbents of Cr(VI) from synthetic solutions and the effect of operating parameters were investigated. The activated rice husk carbon was prepared thermally in two sizes 0.3 and 1.0 mm. The maximum removal of Cr(VI) occurred at pH 2 by activated rice husk and at pH 4 by activated alumina. The amounts of Cr(VI) adsorbed increased with increase in dose of both adsorbents and their contact time. The Freundlich isotherm was applied.     

Adsorption of chromium from aqueous solution by activated alumina and activated charcoal

Cr(VI) is considered to be potentially carcinogenic to humans. Removal of Cr(VI) ions from aqueous solution under different conditions was investigated using activated alumina (AA) and activated charcoal (AC) as adsorbents. Batch mode experiments were conducted to study the effects of adsorbent dose, contact time, pH, temperature and initial concentration of Cr(VI). Results showed that the adsorption of Cr(VI) depended significantly on pH and temperature. Equilibrium studies showed that Cr(VI) had a high affinity for AA at pH 4 and AC at pH 2. For AA, maximum adsorption was found at 25 degrees C, indicating exothermic adsorption, while for AC, maximum adsorption was at 40 degrees C. Freundlich and Langmuir adsorption isotherms were also applied and they showed good fits to the experimental data. The results suggest that both AA and AC could be used as effective adsorbents for the removal of Cr(VI) ions.     

Modeling, simulation, and experimental validation for continuous Cr(VI) removal from aqueous solutions using sawdust as an adsorbent

Continuous adsorption experiments were performed in a fixed-bed adsorption column to evaluate the performance of low-cost adsorbent (sawdust) developed for the removal of Cr(VI) from aqueous solutions. The effects of influencing parameters such as flow rate, mass of adsorbent, initial Cr(VI) concentration were studied and the corresponding breakthrough curves were obtained. The fixed-bed adsorption process parameters such as breakthrough time, total percentage removal of Cr(VI), adsorption exhaustion rate and fraction of unused bed-length were obtained. A mathematical model for fixed-bed adsorption column was proposed by incorporating the effect of velocity variation along the bed-length in the existing model. Pore and solid diffusion models were used to describe the intra-particle mechanism for Cr(VI) adsorption. The proposed mathematical model was validated with the literature data and the experimental data obtained in the present study and the model was found to be good for explaining the behavior of breakthrough curves.     

Removal of chromium(VI) from water and wastewater using surfactant modified coconut coir pith as a biosorbent

Coconut coir pith, an agricultural solid waste was used as biosorbent for the removal of chromium(VI) after modification with a cationic surfactant, hexadecyltrimethylammonium bromide. Optimum pH for Cr(VI) adsorption was found to be 2.0. Reduction of Cr(VI) to Cr(III) occurred to a slight extent during the removal. Langmuir, Freundlich and Dubinin Radushkevich (D-R) isotherms were used to model the adsorption equilibrium data and the system followed all the three isotherms. The adsorption capacity of the biosorbent was found to be 76.3 mg g(-1), which is higher or comparable to the adsorption capacity of various adsorbents reported in literature. Kinetic studies showed that the adsorption obeyed second order and Elovich model. Thermodynamic parameters such as delta G0, delta H0 and delta S0 were evaluated, indicating that the overall adsorption process was endothermic and spontaneous. Effects of foreign anions were also examined. The adsorbent was also tested for the removal of Cr(VI) from electroplating effluent.     

Removal of Cr(VI) from aqueous solutions by adsorption onto hazelnut shell activated carbon: kinetic and equilibrium studies

The adsorption Cr(VI) from aqueous solutions onto hazelnut shell activated carbon was carried out by varying the parameters such as pH, initial Cr(VI) concentration and temperature. The experimental data fitted well to the pseudo first-order kinetic model and then the rate constants were evaluated. The Langmuir isotherm provided the best correlation for Cr(VI) onto the activated carbon. Adsorption capacity was calculated from the Langmuir isotherm as 170 mg/g at an initial pH of 1.0 for the 1000 mg/l Cr(VI) solution. Thermodynamic parameters were evaluated and the adsorption is endothermic showing monolayer adsorption of Cr(VI).     

Adsorption of heavy metal ions from aqueous solutions by activated carbon prepared from apricot stone

Apricot stones were carbonised and activated after treatment with sulphuric acid (1:1) at 200 degrees C for 24 h. The ability of the activated carbon to remove Ni(II), Co(II), Cd(II), Cu(II), Pb(II), Cr(III) and Cr(VI) ions from aqueous solutions by adsorption was investigated. Batch adsorption experiments were conducted to observe the effect of pH (1-6) on the activated carbon. The adsorptions of these metals were found to be dependent on solution pH. Highest adsorption occurred at 1-2 for Cr(VI) and 3-6 for the rest of the metal ions, respectively. Adsorption capacities for the metal ions were obtained in the descending order of Cr(VI) > Cd(II) > Co(II) > Cr(III) > Ni(II) > Cu(II) > Pb(II) for the activated carbon prepared from apricot stone (ASAC).     

Batch removal of chromium(VI) from aqueous solution by Turkish brown coals

The ability of using low-rank Turkish brown coals (Ilgın: BC₁, Beyşehir: BC₂, and Ermenek: BC₃) to remove Cr(VI) from aqueous solutions was studied as a function of contact time, solution pH, temperature, concentration of metal solutions and amount of adsorbent. Their sorption properties were compared with the activated carbon from Chemviron (AQ-30). Adsorption of Cr(VI) uptake is in all cases pH-dependent showing a maximum at equilibrium pH values between 2.0 and 3.2, depending on the biomaterial, that correspond to initial pH values of 2.3 units for BC₁, 3.0 units for BC₂ and 3.2 units for BC₃ and AQ-30. Batch equilibrium tests showed that the Cr(VI) removal was fitted with Freundlich isotherm and the adsorption reached equilibrium in 80 min. It was proceeding effectively into a short acid pH interval (2.0–3.2) where processes of Cr(VI) sorption are maximized. It was observed that the maximum adsorption capacity of 11.2 mM of Cr(VI)/g for Ilgın (BC₁), 12.4 mM of Cr(VI)/g for Beyşehir (BC₂), 7.4 mM of Cr(VI)/g for Ermenek (BC₃) and 6.8 mM of Cr(VI)/g for activated carbon (AQ-30) was achieved at pH of 3.0. The rise in temperature caused a slight decrease in the value of the equilibrium constant (K_c) for the sorption of Cr(VI) ion. The Cr(VI) sorption capacities of Beyşehir and Ilgın brown coals were the same. Ermenek brown coals and activated carbon (AQ-30) showed a similar sorption capacity.     

Column study on the adsorption of Cr(III) and Cr(VI) using Pumice, Yarikkaya brown coal, Chelex-100 and Lewatit MP 62

In the present study, adsorption of Cr(III) and Cr(VI) on Pumice (Pmc), Yarikkaya (YK) brown coal, Chelex-100, and Lewatit MP 62 is examined at room temperature and at initial chromium concentration of 1.0 x 10(-3) mol/L. Column method was carried out as a function of pH, concentration of Cr(III) and Cr(VI) ions, volume of samples and flow rate. The experimental data were evaluated by Freundlich and Langmuir isotherm models. The dynamic breakthrough capacities of the adsorbents for Cr(III) and Cr(VI) were calculated. The maximum chromium sorption occurred at 5 mL/min flow rate and 25 mL volume for all adsorbents. The results showed that the two readily available adsorbents namely Pmc and YK, were suitable for removing chromium from aqueous solution.     

Use of low-cost biological wastes and vermiculite for removal of chromium from tannery effluent

Biological wastes (sawdust, rice husk, coirpith and charcoal) and a naturally occurring mineral (vermiculite) have been tested for their effectiveness in removing Cr from tannery effluent through batch and column experiments. The adsorption capacities of the substrates were also evaluated using isotherm tests and computing distribution co-efficient. The sawdust exhibited a higher adsorption capacity (k = 1482 mgkg(-1)), followed by coirpith (k = 159 mgkg(-1)). The biosorbent and mineral vermiculite in columns were found very effective in removing Cr from tannery effluent. About 94% removal of Cr was achieved by a column of coirpith, and equally (93%) by a column containing a mixture of coirpith and vermiculite. This study showed that biological wastes are potential adsorbents of Cr, which could be successfully used to reduce the Cr concentrations in tannery effluent.     

Potential use of green algae as a biosorbent for hexavalent chromium removal from aqueous solutions

The hexavalent chromium Cr(VI) poses a threat as a hazardous metal and its removal from aquatic environments through biosorption has gained attention as a viable technology of bioremediation. We evaluated the potential use of three green algae (Cladophora glomerata, Enteromorpha intestinalis and Microspora amoena) dry biomass as a biosorbent to remove Cr(VI) from aqueous solutions. The adsorption capacity of the biomass was determined using batch experiments. The adsorption capacity appeared to depend on the pH. The optimum pH with the acid-treated biomass for Cr(VI) biosorption was found to be 2.0 at a constant temperature, 45?°C. Among the three genera studied, C. glomerata recorded a maximum of 66.6% removal from the batch process using 1.0?g dried algal cells/100?ml aqueous solution containing an initial concentration of 20?mg/L chromium at 45?°C and pH 2.0 for 60?min of contact time. Langmuir and Freundlich isotherm equations fitted to the equilibrium data, Freundlich was the better model. Our study showed that C. glomerata dry biomass is a suitable candidate to remove Cr(VI) from aqueous solutions.     

Removal of chromium from industrial waste by using eucalyptus bark

Several low cost biomaterials such as baggase, charred rice husk, activated charcoal and eucalyptus bark (EB) were tested for removal of chromium. All the experiments were carried out in batch process with laboratory prepared samples and wastewater obtained from metal finishing section of auto ancillary unit. The adsorbent, which had highest chromium(VI) removal was EB. Influences of chromium concentration, pH, contact time on removal of chromium from effluent was investigated. The adsorption data were fitted well by Freundlich isotherm. The kinetic data were analyzed by using a first order Lagergren kinetic. The Gibbs free energy was obtained for each system and was found to be -1.879 kJ mol(-1) for Cr(VI) and -3.885 kJ mol(-1) for Cr(III) for removal from industrial effluent. The negative value of deltaG0 indicates the feasibility and spontaneous nature of adsorption. The maximum removal of Cr(VI) was observed at pH 2. Adsorption capacity was found to be 45 mg/g of adsorbent, at Cr(VI) concentration in the effluent being 250 mg/l. A waste water sample containing Cr(VI), Cr(III), Mg, and Ca obtained from industrial unit showed satisfactory removal of chromium. The results indicate that eucalyptus bark can be used for the removal of chromium.     

Development of a new Cr(VI)-biosorbent from agricultural biowaste

Among useless but abundant agricultural biowastes such as banana skin, green tea waste, oak leaf, walnut shell, peanut shell and rice husk, in this study, banana skin was screened as the most efficient biomaterial to remove toxic Cr(VI) from aqueous solution. X-ray photoelectron spectroscopy (XPS) study revealed that the mechanism of Cr(VI) biosorption by banana skin was its complete reduction into Cr(III) in both aqueous and solid phases and partial binding of the reduced-Cr(III), in the range of pH 1.5-4 tested. One gram of banana skin could reduce 249.6 (+/-4.2)mg of Cr(VI) at initial pH 1.5. Namely, Cr(VI)-reducing capacity of banana skin was four times higher than that of a common chemical Cr(VI)-reductant, FeSO(4).7H(2)O. To diminish undesirable/serious organic leaching from the biomaterial and to enhance removal efficiency of total Cr, its powder was immobilized within Ca-alginate bead. The developed Cr(VI)-biosorbent could completely reduce toxic Cr(VI) to less toxic Cr(III) and could remove almost of the reduced-Cr(III) from aqueous phase. On the basis of removal mechanisms of Cr(VI) and total Cr by the Cr(VI)-biosorbent, a kinetic model was derived and could be successfully used to predict their removal behaviors in aqueous phase. In conclusion, our Cr(VI)-biosorbent must be a potent candidate to substitute for chemical reductants as well as adsorbents for treating Cr(VI)-bearing wastewaters.     

Low-cost supports used to immobilize fungi and reliable technique for removal hexavalent chromium in wastewater

The main goal of this study was to exploit low-cost and efficient sorbents for the removal and recovery of Cr(VI) in wastewater. Three supports of sawdust, polyurethane and alginate were applied to immobilize living and dead R. cohnii cells, respectively. There was a distinct increase in the Cr(VI) removal efficiency before and after the HCl-pretreatment. Langmuir adsorption isotherm model was well used to describe the distribution of Cr(VI) between the liquid and solid phases in batch studies. The values of q0 predicted by Thomas model were near to experimental ones in the experiments of packed column. The breakthrough curves calculated with this model were consistent well with experimental ones at a largely extent. Desorption, regeneration and reuse of the packed column were studied. After 5 cycles, adsorption capacity was still kept at higher level, reaching to 91.4, 87.9, 91.4 and 93.3mg/l contrasted with the first cycle (94.1, 90.4, 94.8 and 98.5mg/l) and the desorption efficiency were 85.0%, 96.2%, 93.4% and 91.4% compared with the first cycle (87.6%, 95.4%, 96.7% and 94.3%), corresponding to living cells immobilized with sawdust, polyurethane, and dead cells immobilized with polyurethane and alginate, respectively. The results indicated that the packed columns with the immobilized living and dead R. cohnii cells were the better option to adsorb, desorb and recover Cr(VI) from wastewater.     

Immobilized chitosan as biosorbent for the removal of Cd(II), Cr(III) and Cr(VI) from aqueous solutions

The generation of layer-by-layer silicate-chitosan composite biosorbent was studied. The films were evaluated on its stability regarding the polymer leakage and its capability in the removal of Cd(II), Cr(III) and Cr(VI) from an aqueous solution. SEM, EDAX and ATR-IR techniques were applied for material characterization. Silicate-chitosan films with a final layer of silicate demonstrated chitosan retention and had better sorption capacities than those without it. For metal species, such as Cd(II) and Cr(III), the greatest adsorption was obtained when the pH of the solution was 7. When Cr(VI) was evaluated, pH 4 was the optimal for its adsorption. Langmuir and Freundlich isotherms were modeled for the equilibrium data. An 80% of the adsorbed metal was recovered by HNO(3) incubation. This non-covalent immobilization method allowed chitosan surface retention and did not affect its adsorption properties. The use of a coated surface would facilitate sorbent removal from medium after adsorption.     

The removal of chromium(VI) from aqueous solutions by Fagus orientalis L

The removal of chromium(VI) from aqueous solution under different conditions using an adsorbent was investigated. This adsorbent is Beech (Fagus orientalis L.) sawdust studied by using batch techniques. Batch studies indicated that the percent adsorption decreased with increasing initial concentration of chromium(VI). A contact time of 80 min was found to be optimum. Maximum chromium(VI) removal was observed near a pH of 1.0. Adsorption conformed to the Freundlich and Langmuir isotherms.     

Hexavalent chromium reduction by bacterial consortia and pure strains from an alkaline industrial effluent

Aims: To characterize the bacterial consortia and isolates selected for their role in hexavalent chromium removal by adsorption and reduction. Methods and Results: Bacterial consortia from industrial wastes revealed significant Cr(VI) removal after 15 days when incubated in medium M9 at pH 6·5 and 8·0. The results suggested chromium reduction. The bacterial consortia diversity (T‐RFLP based on 16S rRNA gene) indicated a highest number of operational taxonomic units in an alkaline carbonate medium mimicking in situ conditions. However, incubations under such conditions revealed low Cr(VI) removal. Genomic libraries were obtained for the consortia exhibiting optimal Cr(VI) removal (M9 medium at pH 6·5 and 8·0). They revealed the dominance of 16S rRNA gene sequences related to the genera Pseudomonas/Stenotrophomonas or Enterobacter/Halomonas, respectively. Isolates related to Pseudomonas fluorescens and Enterobacter aerogenes were efficient in Cr(VI) reduction and adsorption to the biomass. Conclusions: Cr(VI) reduction was better at neutral pH rather than under in situ conditions (alkaline pH with carbonate). Isolated strains exhibited significant capacity for Cr(VI) reduction and adsorption. Significance and Impact of Study: Bacterial communities from chromium‐contaminated industrial wastes as well as isolates were able to remove Cr(VI). The results suggest a good potential for bioremediation of industrial wastes when optimal conditions are applied.     

Hexavalent chromium removal from aqueous solutions by a novel powder prepared from Colocasia esculenta leaves

In this study, batch removal of hexavalent chromium from aqueous solutions by powdered Colocasia esculenta leaves was investigated. Batch experiments were conducted to study the effects of adsorption of Cr(VI) at different pH values, initial concentrations, agitation speeds, temperatures, and contact times. The biosorbent was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectrometer analysis. The biosorptive capacity of the adsorbent was dependent on the pH of the chromium solution in which maximum removal was observed at pH 2. The adsorption equilibrium data were evaluated for various adsorption isotherm models, kinetic models, and thermodynamics. The equilibrium data fitted well with Freundlich and Halsey models. The adsorption capacity calculated was 47.62 mg/g at pH 2. The adsorption kinetic data were best described by pseudo-second-order kinetic model. Thus, Colocasia esculenta leaves can be considered as one of the efficient and cheap biosorbents for hexavalent chromium removal from aqueous solutions.     

Biosorption of chromium(VI) in aqueous solutions by chemically modified Strychnine tree fruit shell

Chromium(VI) was removed from aqueous solution using sulfuric- and phosphoric-acid-activated Strychnine tree fruit shells (SSTFS and PSTFS) as biosorbents. Effects of various parameters such as adsorbent dose (0.02–0.1 g/L), temperature (303–333 K), agitation speed, solution pH (2–9), contact time, and initial Cr(VI) concentration (50–250 mg/L) were studied for a batch adsorption system. The optimum pH range for Cr(VI) adsorption was determined as 2. Equilibrium adsorption data were analyzed with isotherm models and the Langmuir and Freundlich models got best fitted values for SSTFS (R² value – 0.994) and PSTFS (R² value – 0.996), respectively. The maximum adsorption capacities of SSTFS and PSTFS were 100 and 142.85 mg/g, respectively. The biosorption process was well explained by pseudo-second-order kinetic model with higher R² value (SSTFS – 0.996, PSTFS – 0.990) for both biosorbents. Characterization of biosorbents was done using Fourier transform infrared spectroscopy, scanning electron microscopy, elemental analysis, energy-dispersive X-ray analysis, and thermogravimetric analysis. Thermodynamic studies revealed the spontaneous, endothermic, and randomness in nature of the Cr(VI) adsorption process. Different concentrations of NaOH solutions were used to perform the desorption studies. The results demonstrated that both SSTFS and PSTFS can be used as an effective and low-cost biosorbent for removal of Cr(VI) from aqueous solutions.     

Hexavalent chromium removal from aqueous solution by adsorption on treated sawdust

The studies on adsorption of hexavalent chromium were conducted by varying various parameters such as contact time, pH, amount of adsorbent, concentration of adsorbate and temperature. The kinetics of adsorption of Cr(VI) ion followed pseudo second order. Langmuir adsorption isotherm was employed in order to evaluate the optimum adsorption capacity of the adsorbent. The adsorption capacity was found to be pH dependant. Sawdust was found to be very effective and reached equilibrium in 3 h (adsorbate concentration 30 mg l⁻¹). The rate constant has been calculated at 303, 308, 313 and 318 K and the activation energy (E_a) was calculated using the Arrhenius equation. Thermodynamic parameters such as standard Gibbs energy (ΔG°) and heat of adsorption (ΔH_r) were calculated. The ΔG° and ΔH_r values for Cr(VI) adsorption on the sawdust showed the process to be exothermic in nature. The percentage of adsorption increased with decrease in pH and showed maximum removal of Cr(VI) in the pH range 4.5–6.5 for an initial concentration of 5 mg l⁻¹.