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The metal chromium is used mainly for making steel and other alloys. Chromium compounds, in either the chromium (III) or chromium (VI) forms, are used for chrome plating, the manufacture of dyes and pigments, leather and wood preservation and treatment of cooling tower water. Smaller amounts are used in drilling muds, textiles, and toner for copying machines.
This section provides details on the recent research and developments in the chromium removal system. The novel methods followed today include:
- Current Wastewater Treatment Process - Chromium Removal
- New Technologies in Chromium Removal from Wastewater
- A Novel Technology for Biosorption and Recovery Hexavalent Chromium in Wastewater by Bio-Functional Magnetic Beads
- Effect of Rhamnolipids on Chromium-Contaminated Kaolinite
- Removal of Chromium from Water and Wastewater by Ion Exchange Resins
- Modified Activated Carbon for the Removal of Copper, Zinc, Chromium and Cyanide from Wastewater
- Removal of Chromium(VI) from Wastewater by Combined Electrocoagulation–Electroflotation without A Filter
- Trivalent Chromium Removal from Wastewater Using Low Cost Activated Carbon Derived from Agricultural Waste Material and Activated Carbon Fabric Cloth
- Removal of Lead and Chromium from Wastewater Using Bagasse Fly Ash—A Sugar Industry Waste
Current Wastewater Treatment Process - Chromium Removal
Chromium has a large influence upon drinking water quality. It cannot normally be found in groundwater and surface water in considerable concentrations. Specific removal in sewage water treatment is therefore unusual. Chromium removal from water is optional, because both ion exchangers and active carbon can be applied for this purpose.
Chromium (III) may precipitate as hydroxide. Coagulation is not a very effective mechanism of chromium (VI) removal. When iron sulphate is applied chromium (VI) may be reduced to chromium (III) by means of iron ions, and it can then be removed. This method is however very unusual in drinking water preparation.
New Technologies in Chromium Removal from Wastewater
A Novel Technology for Biosorption and Recovery Hexavalent Chromium in Wastewater by Bio-Functional Magnetic Beads
The goal of this study was to develop an applied technique for the removal and recovery of heavy metal in wastewater. It is novel that the Cr(VI) could be adsorbed and recovered by bio-functional magnetic beads. Furthermore, the magnetic separation technology would make their separation more convenient. The beads were constituted by the powder of Rhizopus cohnii and Fe3O4 particles coated with alginate and polyvinyl alcohol (PVA). The parameters effecting Cr(VI) removal were obtained: the optimum pH 1.0 and optimum temperature 28 °C. The biosorption took place mainly in form of Cr(VI) and R. cohnii biomass played a key role in Cr(VI) adsorption. The groups of , –, and NH– played an important role in the Cr(VI) adsorption. Consequently, the beads exhibited the superior performances in Cr(VI) cleanup, separation and recovery and the perspective potential in application.Candida sp.was also found to be effiecient in the removal of chromium ions in wastewater (Flor de María Guillén-Jiménez, et al., and Jinshao Yeet al.,).1
Effect of Rhamnolipids on Chromium-Contaminated Kaolinite
Hexavalent chromium Cr(VI) is a common environmental pollutant that is treated by its reduction to the trivalent form Cr(III). The latter can be re-oxidized to the toxic form, Cr(VI), under specific conditions. A study was conducted on the removal of Cr(III) to eliminate the hazard imposed by its presence in soil as there has been some evidence that organic compounds can decrease its sorption. The effect of addition of negatively-charged biosurfactants (rhamnolipids) on chromium contaminated kaolinite was studied. Results showed that the rhamnolipids have the capability of extracting 25% portion of the stable form of chromium, Cr(III), from the kaolinite, under optimal conditions. The removal of hexavalent chromium was also enhanced compared to water by a factor of 2 using a solution of rhamnolipids. Results from the sequential extraction procedure showed that rhamnolipids remove Cr(III) mainly from the carbonate and oxide/hydroxide portions of the kaolinite. The rhamnolipids had also the capability of reducing close to 100% of the extracted Cr(VI) to Cr(III) over a period of 24 days. This study indicated that rhamnolipids could be beneficial for the removal or long-term conversion of chromium Cr(VI) to Cr(III).2
Removal of Chromium from Water and Wastewater by Ion Exchange Resins
Removal of chromium from water and wastewater is obligatory in order to avoid water pollution. Batch shaking adsorption experiments were carried out to evaluate the performance of IRN77 and SKN1 cation exchange resins in the removal of chromium from aqueous solutions. The percentage removal of chromium was examined by varying experimental conditions viz., dosage of adsorbent, pH of the solution and contact time. It was found that more than 95% removal was achieved under optimal conditions. The adsorption capacity (k) for chromium calculated from the Freundlich adsorption isotherm was found to be 35.38 and 46.34 mg/g for IRN77 and SKN1 resins, respectively. The adsorption of chromium on these cation exchange resins follows the first-order reversible kinetics. The ion exchange resins investigated in this study showed reversible uptake of chromium and, thus, have good application potential for the removal/recovery of chromium from aqueous solutions.3
Modified Activated Carbon for the Removal of Copper, Zinc, Chromium and Cyanide from Wastewater
Modified activated carbon are carbonaceous adsorbents which have tetrabutyl ammonium iodide (TBAI) and sodium diethyl dithiocarbamate (SDDC) immobilised at their surface. This study investigates the adsorption of toxic ions, copper, zinc, chromium and cyanide on these adsorbents that have undergone surface modification with tetrabutyl ammonium (TBA) and SDDC in wastewater applications. The modification technique enhance the removal capacity of carbon and therefore decreases cost-effective removal of Cu(II), Zn(II), Cr(VI) and CN− from metal finishing (electroplating unit) wastewater. Two separate fixed bed modified activated carbon columns were used; TBA-carbon column for cyanide removal and SDDC-carbon column for multi-species metal ions (Cu, Zn, Cr) removal. Wastewater from electroplating unit containing 37 mg l−1 Cu, 27 mg l−1 Zn, 9.5 mg l−1 Cr and 40 mg l−1 CN− was treated through the modified columns. A total CN− removal was achieved when using the TBA-carbon column with a removal capacity of 29.2 mg g−1 carbon. The TBA-carbon adsorbent was found to have an effective removal capacity of approximately five times that of plain carbon. Using SDDC-carbon column, Cu, Zn and Cr metal ions were eliminated with a removal capacity of 38, 9.9 and 6.84 mg g−1, respectively. The SDDC-carbon column has an effective removal capacity for Cu (four times), Zn (four times) and Cr (two times) greater than plain carbon.4
Removal of Chromium (VI) from Wastewater by Combined Electrocoagulation–Electroflotation without a Filter
A combined electrocoagulation and electroflotation process was designed to reduce Cr6+ to Cr3+ first and then to remove the total Cr from wastewater to a value below 0.5 mg/L. Acidic condition was employed in the reduction of Cr6+ and neutral conditions were found to be beneficial for the coagulation of the precipitates of Cr(OH)3 and Fe(OH)3. The formation of Fe(OH)3 was ensured by sparging compressed air in the coagulation unit through a draft tube. The air not only oxidizes Fe2+ produced electrically, but also helps to mix the water for a better coagulation of the particles. The two-stage electroflotation arrangement can separate the solids from the wastewater to a value of less than 3 mg/L with total Cr less than 0.5 mg/L. The residence time required is about 1.2 h. The optimal conditions for the treatment are: charge loading about 2.5 Faradays/m3 water, pH value in the coagulation unit is 5–8. The power consumption is less than 1 kW h/m3 water at the conductivity of 1.5 mS/cm. When aluminum ions are either added or produced in situ in the coagulation unit, the treated wastewater can be discharged without any filtration.5
Trivalent Chromium Removal from Wastewater Using Low Cost Activated Carbon Derived from Agricultural Waste Material and Activated Carbon Fabric Cloth
An efficient adsorption process is developed for the decontamination of trivalent chromium from tannery effluents. A low cost activated carbon (ATFAC) was prepared from coconut shell fibers (an agricultural waste), characterized and utilized for Cr(III) removal from water/wastewater. A commercially available activated carbon fabric cloth (ACF) was also studied for comparative evaluation. All the equilibrium and kinetic studies were conducted at different temperatures, particle size, pHs, and adsorbent doses in batch mode. The Langmuir and Freundlich isotherm models were applied. The Langmuir model best fit the equilibrium isotherm data. The maximum adsorption capacities of ATFAC and ACF at 25 °C are 12.2 and 39.56 mg/g, respectively. Cr(III) adsorption increased with an increase in temperature (10 °C: ATFAC—10.97 mg/g, ACF—36.05 mg/g; 40 °C: ATFAC—16.10 mg/g, ACF—40.29 mg/g). The kinetic studies were conducted to delineate the effect of temperature, initial adsorbate concentration, particle size of the adsorbent, and solid to liquid ratio. The adsorption of Cr(III) follows the pseudo-second-order rate kinetics. From kinetic studies various rate and thermodynamic parameters such as effective diffusion coefficient, activation energy and entropy of activation were evaluated. The sorption capacity of activated carbon (ATFAC) and activated carbon fabric cloth is comparable to many other adsorbents/carbons/biosorbents utilized for the removal of trivalent chromium from water/wastewater.6
Removal of Lead and Chromium from Wastewater Using Bagasse Fly Ash-A Sugar Industry Waste
An inexpensive and effective adsorbent was developed from bagasse fly ash, obtained from a sugar industry, for the dynamic uptake of lead and chromium. Lead and chromium are sorbed by the developed adsorbent up to 96–98%. The removal of these two metal ions up to 95–96% was achieved by column experiments at a flow rate of 0.5 ml min−1. The adsorption was found to be exothermic in nature. The adsorbent was successfully tried for the removal of lead and chromium from wastewater in our laboratory. The developed system for the removal of two ions is very useful, economic, rapid, and reproducible.7
1Li H, Li Z, Liu T, Xiao X, Peng Z, Deng L, 2008. A novel technology for biosorption and recovery hexavalent chromium in wastewater by bio-functional magnetic beads.Bioresour Technol. 99(14):6271-9
2Hafez Massara; Catherine N. Mulligan, John Hadjinicolaou, 2007. Effect of Rhamnolipids on Chromium-Contaminated Kaolinite. Soil and Sediment Contamination, 16 (1 – 14).
3Rengaraj S, Kyeong-Ho Yeon and Seung-Hyeon Moon, 2001. Removal of chromium from water and wastewater by ion exchange resins. Journal of Hazardous Materials, 87 (273- 287).
4Lotfi Monser and Nafaâ Adhoum, 2002. Modified activated carbon for the removal of copper, zinc, chromium and cyanide from wastewater. Separation and Purification Technology, 26 (137- 146).
5Ping Gao, Xueming Chen, Feng Shen and Guohua Chen, 2005. Removal of chromium(VI) from wastewater by combined electrocoagulation–electroflotation without a filter. Separation and Purification Technology, 43 (117- 123).
6Dinesh Mohan, Kunwar P. Singh and Vinod K. Singh, 2006. Trivalent chromium removal from wastewater using low cost activated carbon derived from agricultural waste material and activated carbon fabric cloth. Journal of Hazardous Materials, 135 (280- 295).
7GuptaV. K and Imran Ali, 2004. Removal of lead and chromium from wastewater using bagasse fly ash—a sugar industry waste. Journal of Colloid and Interface Science, 271 (321- 328).