Biosorption of chromium(VI) using Bacillus subtilis SS-1 isolated from soil samples of electroplating industry

Soils around the electroplating industry are often polluted with metals. The aim of the study was to assess Cr(VI) adsorption potential of chromium-resistant bacteria isolated from soil samples collected in and around electroplating industry, Coimbatore, India. A total of six morphologically different chromium-resistant bacteria were isolated from the soil samples and assayed for resistance to Cr(VI). Isolate designated SS-1 exhibited maximum resistance to Cr(VI) (600 mg/l) and subsequently identified as Bacillus subtilis based on the morphology, phenotypic characters, and partial 16S rDNA sequences. Batch experiments were carried out as a function of time, initial Cr(VI) concentration (100 mg/l), pH (2), and biosorbent dose (0.1 g/l). The maximum percentage of Cr(VI) removal was found to be 98.7 %. The experimental data showed a better fit with Langmuir model over Freundlich model throughout the range of initial concentrations. The kinetic models were examined with pseudo-first-order and pseudo-second-order kinetics. Fourier transform infrared spectroscopy studies confirmed the involvement of carboxyl and amide groups in Cr(VI) adsorption. Scanning electron microscopic studies revealed that nature of the bioadsorbent was altered after Cr(VI) adsorption. The results revealed that Cr(VI) was considerably adsorbed onto bacterial biomass, and it could be an economical method for the removal of Cr(VI) from aqueous solution.     

Electrokinetic removal of caesium from kaolin

Soil, in the form of kaolin and a sample of natural soil from an industrial site, was artificially contaminated with caesium and subjected to electrokinetic treatment. The effect of catholyte pH control on the process was investigated using different acids to control the catholyte pH. During treatment the in situ pH distribution, the current flow, and the potential distribution were monitored. At the end of the treatment the pore fluid conductivity and the caesium concentration distribution was measured. The results of these experiments showed that for caesium contamination, catholyte pH control is essential in order to create a suitable environment throughout the soil to enable contaminant removal. It was found that the type of acid used to control the catholyte pH affected the rate of caesium removal (nitric, sulphuric, acetic and citric acids were tested). All of the acids tested were effective, but the highest caesium extraction was achieved when nitric acid was used to control the catholyte pH. The relatively high adsorption capacity of the soil for caesium was found to significantly reduce the rate of removal. After 240 h of treatment at 1 Vcm(-1) (using sulphuric acid to control the catholyte pH), less than 80% of the caesium was removed from a 30 cm long sample of kaolin. Electrokinetic treatment of the industrial soil sample was slower than for the kaolin, but a significant extraction rate for caesium was achieved.     

Removal of chromium by riverbed sand from water and wastewater: effect of important parameters

Application of riverbed sand, a non-toxic substance for the removal of Cr(VI) for aqueous solutions has been investigated. Removal of Cr(VI) was dependent on initial concentration and removal increased from 43.2% to 74.3% by decreasing initial concentration from 7.5x10(-5) M to 1.0x10(-5) M at 25 degrees C, 1.0x10(-2) M NaClO4 ionic strength and 100 rpm. Higher removal was obtained at particles of smaller sizes of the adsorbent. Removal decreased from 74.3% to 40.7% by increasing temperature from 25 degrees C to 35 degrees C exhibiting exothermic nature of the process of removal. Thermodynamic parameters, namely change in free energy (DeltaG degrees), enthalpy (DeltaH degrees) and entropy (DeltaS degrees), were calculated and were found to be -0.81 kcal mol(-1), -17.21 kcal mol(-1) and 56.94 cal mol(-1), respectively at 25 degrees C. pH of the solution has pronounced effect on the removal and higher removal was obtained in acidic pH ranges, maximum (74.3%) being at 2.5 pH.     

Effects of pH and dissolved oxygen on Cr(VI) removal in Fe(0)/H2O systems

The effects of pH and dissolved oxygen (DO) on aqueous Cr(VI) removal by micro-scale zero-valent iron (Fe(0)/H(2)O system) were investigated. Batch experiments were conducted at pH 4.0, 5.0 and 6.0 under oxic and anoxic conditions. Column experiments were performed at pH 5.0 and 7.5 under oxic condition. Spectroscopic analyses were applied to explain the mechanism of Cr(VI) removal using X-ray absorption near-edge structure (XANES), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results showed that the kinetics of Cr(VI) removal were fastest at pH 5 under both oxic and anoxic conditions. As a rule, Cr(VI) removal were faster under oxic conditions than under anoxic conditions. Column experiments showed that Cr(VI) removal was about 1.7-fold higher at pH 5 than at pH 7.5. XANES (X-ray absorption near edge structures) results showed that Fe(0) reduced Cr(VI) to Cr(III) under both oxic and anoxic conditions. X-ray diffraction patterns of the Cr(VI)-Fe(0) reaction products suggested partial formation of chromite (FeCr(2)O(4)) at pH 5 and 6 under oxic conditions. However, nano-sized clusters of Cr(III)/Fe(III) hydroxide/oxyhydroxide were formed on the surface of Fe(0) under anoxic conditions. These results indicate that the presence of oxygen in solution plays an important role in control of the kinetic of Cr(VI) removal and in development of various Cr(VI) reduction products.     

Reduction and removal of Cr(VI) from aqueous solutions using modified byproducts of beer production

Biosorption, as an effective and low-cost technology treating industrial wastewaters containing Cr(VI), has become a significant concern worldwide. In this work, acid-modified byproducts of beer production (BBP) were used to remove Cr(VI) from aqueous solutions. Removal of Cr(VI) increases as the pH is decreased from 4.0 to 1.5, but the maximum of total Cr removal is obtained in a pH range from 2.0 to 2.5. Nearly 60% of the initial Cr(VI) (100 mg L(-1)) was adsorbed or reduced to Cr(III) within the first 10 min at pH 2.0. The Cr(VI) removal capability of acid-modified BBP materials was almost completely retained after regenerating with acid. FT-IR and XPS spectra revealed that carboxylate and carboxyl groups on the surface of modified BBP materials play a major role in Cr(VI) binding and reduction, whereas amide and other groups play a minor role in the Cr(VI) removal process.     

Investigation of the potential mobility of Pb, Cd and Cr(VI) from moderately contaminated farmland soil to groundwater in Northeast, China

The adsorption/desorption of Pb, Cd and Cr(VI) on moderately contaminated farmland soils in Northeast China and the effect of pH value on adsorption/desorption were investigated. Soil column leaching experiment was also carried out to further understand the mobility of the three metals in aeration zone of soil. Both Langmuir and Freundlich model gave good fits to the adsorption data of Pb and Cd, while the adsorption data of Cr(VI) followed linear adsorption isotherm. The adsorption/desorption of Pb, Cd and Cr(VI) obtained equilibrium in a few hours. Adsorption amounts of the three metals decreased in the order: Pb>Cd>Cr(VI). Desorption of the metals was insignificant at pH 5.0. Pb and Cd adsorption increased with pH, while Cr(VI) decreased. The effect of pH on desorption was contrary to that of adsorption. Leaching experiment showed that the mobility of these metals followed the order of Cr(VI)>Cd>Pb, which was consistent with the adsorption/desorption study. The results suggest that once soil is polluted by wastewater containing Pb and Cd, Pb and Cd tend to accumulating in topsoil and move downward very slowly, while the mobility of Cr(VI) in soil/groundwater system is much high because only limited amount of Cr(VI) were adsorbed by soil.     

Biosorption of Cr(VI) by immobilized biomass of two indigenous strains of cyanobacteria isolated from metal contaminated soil

Biosorption of Cr(VI) using native strains of cyanobacteria from metal contaminated soil in the premises of textile mill has been reported in this paper. Biosorption was studied as a function of pH (1-5), contact time (5-180 min) and initial chromium ion concentration (5-20mg/l) to find out the maximum biosorption capacity of alginate immobilized Nostoc calcicola HH-12 and Chroococcus sp. HH-11. The optimum conditions for Cr(VI) biosorption are almost same for the two strains (pH 3-4, contact time 30 min and initial chromium concentration of 20mg/l) however, the biomass of Chroococcus sp. HH-11 was found to be more suitable for the development of an efficient biosorbent for the removal of Cr(VI) from wastewater, as it showed higher values of q(m) and K(f), the Langmuir and Freundlich isotherm parameters. Both the isotherm models were suitable for describing the biosorption of Cr(VI) by the cyanobacterial biosorbents.     

Biosorption of chromium species by aquatic weeds: kinetics and mechanism studies

In this paper, we have presented the results of Cr(VI) and Cr(III) removal from aqueous phase by different aquatic weeds as biosorbents. Batch kinetic and equilibrium experiments were conducted to determine the adsorption kinetic rate constants and maximum adsorption capacities of selected biosorbents. In most of the cases, adsorption followed a second-order kinetics. For Cr(III), maximum adsorption capacity was exhibited by reed mat (7.18mg/g). In case of Cr(VI), mangrove leaves showed maximum removal/reduction capacity (8.87mg/g) followed by water lily (8.44mg/g). There was a significant difference in the concentrations of Cr(VI) and total chromium removed by the biosorbents. In case of Cr(VI) removal, first it was reduced to Cr(III) with the help of tannin, phenolic compounds and other functional groups on the biosorbent and subsequently adsorbed. Acid treatment significantly increased Cr(VI) removal capacity of the biosorbents whereas, alkali treatment reduced the Cr(VI) removal capacities of the biosorbents. FTIR spectrum showed the changes in functional groups during acid treatment and biosorption of Cr(VI) and Cr(III). Aquatic weeds seem to be a promising biosorbent for the removal of chromium ions from water environment.     

Enhancement of electrokinetic remediation of hyper-Cr(VI) contaminated clay by zero-valent iron

This paper investigated the effectiveness of incorporating zero-valent iron (ZVI) into electrokinetic (EK) to remediate hyper-Cr(VI) contaminated clay (2497 mg/kg). A ZVI wall was installed in the center of the soil specimen and was filled with 1:1 (w/w) ratio of granular ZVI and sand. Results show that transport of H(+) is greatly retarded by the strong opposite migration of anionic chromate ions, whereupon a revered electroosmosis flow (EO) was resulted and alkaline zone across the specimen was developed promoting the release of Cr(VI) from the clay. Chromium removal was characterized by high Cr(VI) concentration occurred in the anolyte and the presence of Cr(III) precipitates in the catholyte. The Cr(VI) reduction efficiencies for the process without ZVI wall were 68.1 and 79.2% for 1 and 2V/cm, respectively. As ZVI wall was installed, the corresponding reduction efficiencies increased to 85.8 and 92.5%. The costs for energy and ZVI utilized in this process are US$ 41.0 and 57.5 per cubic meter for the system with electric gradient of 1 and 2V/cm, respectively. The role of ZVI wall effectively reducing Cr(VI) contamination and the operation simultaneous collection of Cr(VI) from the electrode reservoirs are two major advantages of this process.     

Cr(VI) removal from aqueous solution using chemically reduced and functionalized graphene oxide

Chemically reduced and functionalized graphene oxide (GO) was prepared by refluxing of GO with ethylenediamine (ED) using dimethyl formamide (DMF) as solvent. It was confirmed that both ED and DMF contributed to the reduction and functionalization of GO. The resulting adsorbent (ED–DMF–RGO) with amine groups was highly efficient in removing Cr(VI) from its aqueous solution and could be easily separated by filtration. The optimum pH for total Cr removal was observed at pH 2.0 and the Cr(VI) removal capacity of ED–DMF–RGO at this pH was 92.15 mg g^?1, which was about 27 times higher than that of activated carbon, even nearly 4–8 times higher than that of various modified activated carbons. The presence of other ions such as Na⁺, K⁺, Ca²⁺, Cl^?, and Br^? had little effect on the removal of Cr(VI). Interestingly, Cr(VI) was reduced to low-toxic Cr(III) during the adsorption process, which followed an indirect reduction mechanism. Both the Cr(VI) adsorption and subsequent reduction of adsorbed Cr(VI) to Cr(III) contributed to the Cr(VI) removal. The obtained ED–DMF–RGO may be applicable in Cr(VI) removal if they are produced on a large scale and at low price in near future.