Project Completion Report for the Network Project entitled Treatment/Bioremediation of Electroplating and Leather Tanning Effluents Containing Chromium COR – 008 (ILP – 013) {A Network Project of CSIR, New Delhi under Xth Five Year Plan}

Heavy metals are toxic substance that once discharged into water bodies as industrial waste cause environmental pollution. Chromium is an important non-ferrous metal finding its application in electroplating industries for surface treatment and finishing of metals/plastics. This leads to the generation of effluents and solid wastes containing chromium, which causes environmental pollution. Due to stringent laws, which have come into existence world over, pollution related problems and their control are of prime concern. Besides environmental aspects, sufficiently large amounts of metals are disposed off resulting in enhanced burden on the depleting primary resources like ores and minerals. It is therefore essential to look for not only removal-disposal approaches mostly employed as a versatile technique but also to explore recover/reuse methods which can meet the twin objectives of achieving pollution norms and producing value added products/resources recovery from the waste streams thus conserving the natural resources. In this project waste electroplating solutions and leather tanning effluents were identified for the recovery and reuse of chromium by solvent extraction, ion exchange, electrodialysis, bioremediation and adsorption techniques. Recovery hexavalent chromium from an electroplating effluent by solvent extraction with tributylphosphate (TBP) as an extractant was studied. The results demonstrate that chromium(VI) is extracted as HCrO 3 Cl.2TBP in acidic chloride medium and loading capacity of TBP for chromium(VI) was found to be 178 g/L. Stripping of chromium(VI) form loaded TBP was also studied. With 0.1N NaOH solution chromium(VI) was stripped quantitatively from loaded organic. TBP was also used to recover chromium(VI) and zinc from real electroplating effluent collected from an electroplating industry of Jamshedpur. By solvent extraction with TBP and selective stripping with 10% H 2 SO 4 and 1N NaOH 76.1% of zinc and 92.6% chromium(VI) were recovered. The raffinate from the extraction process contains 3.5 ppm chromium which may be safely discharged in the stream after one more stage of SX with TBP. In order to reduce environmental pollution and conserve the natural resources extraction of chromium(VI) from a model solution containing 50-500 ppm chromium(VI) similar to that of an effluent of electroplating unit by ion exchange process was studied using Amberlite IRA 400 and IRA 900 resins. Extraction efficiencies of both the resins were found to be almost comparable. The effect of various parameters such as contact time, pH, concentration of aqueous feed on the extraction of chromium(VI) was investigated. With Amberlite IRA 400 resin sorption of chromium satisfies both Langmuir isotherm and Freundlich isotherm and with Amberlite IRA 900 sorption system follows Freundlich isotherm. Higher value of k f and 1/n in both the cases shows that the process of sorption is governed by chemical reaction with resin. The extraction of chromium(VI) with both the resins follows second order kinetics and found to be pH dependent. Eluition studies showed that 20% sodium hydroxide is required for complete elution of chromium(VI) from Amberlite IRA 400, and 30% sodium hydroxide is required for elution from Amberlite IRA 900 resin. The raffinate of the extraction process contains only 1.5 ppm chromium(VI) which can further be reduced by increasing resin dose. Ion exchange process was also used for the recovery of chromium(III) from a model solution of a tannery. A cation exchanger with sulphonic acid group-Amberlite IR 120 as sodium salt was used to reduce chromium(III) content below the discharge limit of an effluent. Extraction of chromium with Amberlite IR 120 is dependent on initial pH of the solution. Maximum metal extraction with this resin takes place in pH range 1.5-4.5. Sorption of chromium(III) on Amberlite IR 120 was found to follow Freundlich isotherm with higher values of k f and 1/n suggesting that the process of sorption of chromium(III) is mainly governed by chemical reaction with the resin. For elution of chromium(III) from loaded resin it requires high concentration of eluant. With 20% sulphuric acid solution 94.3% chromium(III) was eluted from loaded resin. Aspergillus niger obtained from Microbial Type Culture Collection Center, IMTECH Chandigarh, India was used for biosorption of trivalent chromium. The fungal species when fully grown were adapted on trivalent chromium in concentrations up to 2.5g/L in Czapek Dox Broth at 30oC and pH 2.5. The fungal species adapted on higher concentrations (1000ppm and 2000ppm) of Cr(III) were employed for biosorption experiments. For biosorption experiments at 1000ppm Cr(III) concentration, 63% biosorption occurs in 24 hours when incubated with 1.0g fungal biomass originally adapted on 1000ppm Cr(III), sonicated and simultaneously pre-treated with 0.5N NaOH at pH 2.0-2.5 and 35oC. In 2000ppm Cr(III) solution, 52% biosorption was recorded in 24h using alkali-treated biomass. The experiments were analysed with different isotherms indicating best fit to Freundlich isotherm. Upon evaluating the kinetics of the process using Lagergren expressions, biosorption of Cr(III) on A.niger follows second order kinetics. A. laboratory pilot electrodialysis set up was procured and installed to remove sodium salt from spent tanning bath solution. It was found that within 30 min of electrodialysis 85% salt was removed from the spent bath solution. The diluate containing low salt (NaCl) with total chromium can be recycled to the tanning hides. Further experiments have been planned to optimize the process parameters for removal of sodium chloride from the leather tanning effluent