ADVANCE TREATMENT FOR REMOVAL OF CHROMIUM AND FLUORIDE FROM INDUSTRIAL WASTEWATER

Abstract

The water pollution is enhanced due to high industrialization and random discharge of toxic metal ions, chemical, organic compounds, toxic chemicals, from various industries. The chromium and fluoride like toxic ions are coming in to wastewater from electronic process industries. Especially in the semiconductor industry for wafer surface etching process produces some waste like chromic acids, sulfuric, phosphoric, hydrofluoric etc. Thus, Cr(VI) and fluoride like toxic ions are found in semiconductor effluents. Cr(VI) also coming in waste stream from other industrial activities like steel-works, metal finishing, electroplating, petroleum refining, leather tanning, etc. The high release of fluoride into water bodies of environment from industries such as semiconductor manufacturing, electroplating, glass and ceramic production and many more. Cr(VI) is highly toxic, carcinogenic and tera-togenic. It is harmful for human, animals and plants causing harmful effects on human like lung cancer, damage to liver, kidney and gastric system. General sign of high fluoride consumption is fluorosis, which is identified by mottling of teeth in mild cases and embrittlement of bones and neurological damage in severe cases. The permissible limit as per CPCB standards for Cr (VI) discharge of industrial effluents in different water bodies, viz., inland surface water, public sewers and marine coastal areas are 0.1, 2.0 and 1.0 mg/L, respectively (CPCB 2012). The permissible limit as per CPCB standards for fluoride discharge of industrial effluents is 15 mg/L (CPCB 2012). The fluoride effluent limit as per USEPA from the wastewater treatment facilities has been set to 4 mg/L (USEPA 1985, 2008). In the present study membrane separation (nanofiltration and reverse osmosis) and capacitive deionization process have been selected for simultaneous removal of Cr (VI) and fluoride. In membrane separation various commercial polyamide flat sheet membranes namely NF300, NF500, PN40 and RO membrane were selected for the simultaneous removal of Cr(VI) and fluoride from synthetic and industrial wastewater. The present work aims to study the influence of various operating variables to remove Cr(VI) and fluoride simultaneously from feed synthetic and real industrial wastewater with various nanofiltration (NF300, NF500, PN40) and RO flat sheet membranes. The characterization studies for identification of morphology, surface roughness and chemical composition of NF300, NF500, PN40, RO membranes were carried out with SEM, AFM, and FTIR, respectively. In this experiment influence of pressure on removal of Cr(VI) and fluoride ii was studied by changing the pressure from 2 to 10 bar with a concentration range of 5-100 mg/L of Cr(VI) and fluoride each and at different pH (2 to 10). It was observed that the simultaneous rejection of Cr(VI) and fluoride ions increases with the increase in feed pressure and decreases with an increase in feed concentration. This rejection of Cr(VI) and fluoride ions were significantly influenced by the pH of feed solution. The optimized values of experimental parameters were evaluated found and the optimized value of operating pressure was 10 bar for nanofiltration and 16 bar for reverse osmosis, pH 8 was found best for simultaneous rejection of Cr(VI) and fluoride ions. The highest percent rejection of Cr(VI) and fluoride were found to be 97% and 92% with NF300; 91% and 84% with NF500 and 88% and 82% with PN40 membranes for lower concentration of 5 mg/L feed, respectively. The highest removal of Cr(VI) and fluoride by RO flat sheet membrane were found 99.98% and 95.1% for 5 mg/L feed respectively at 16 bar pressure. The highest percent rejection of Cr(VI) and fluoride were found to be 77% and 70% with NF300; 71% and 64% with NF500 and 68% and 61% with PN40 membranes for higher concentration 100 mg/L feed, respectively. The highest removal of Cr(VI) and fluoride by RO flat sheet membrane were found 99.10% and 94% for 100 mg/L feed, respectively at 16 bar pressure. The rejection performances of membranes are found in the sequence as RO > NF300 > NF500> PN40. The maximum percent rejection of Cr(VI) and fluoride were found 92.2% and 83% with NF300; 99.96% and 94.97% with RO flat sheet membrane from industrial wastewater concentration [11 mg/L Cr(VI) and 35.24 mg/L fluoride ] respectively. The estimation of membrane transport parameters and membrane performance evaluation were carried out with CFSK model and CFSD model. The values of flux and rejection estimated using membrane transport parameters are in good agreement with the experimental results. Reasonably good agreement for experimental rejection and true rejection for Cr(VI) and fluoride estimated by CFSK and CFSD models respectively, but CFSK model predicted values are more accurate compared to CFSD model. The capacitive deionization is recently developing and worldwide attracted techniques due to eco-friendly, having less energy consumption and less working costs than other desalination technologies, simplicity in regeneration and maintenance compared with other conventional techniques of desalination. The CDI technology is used in the application of the desalination and water treatment application. In this work, different activated carbon were prepared from tea waste biomass, rice husk, and limonia acidissma (wood apple) shell with acid treatment and thermal modification. The TGA, iii DTA, DTG analyses of waste biomass were carried out using a thermal analysis instrument. The characterization of prepared activated carbon was done for morphological, chemical composition analysis using SEM and FTIR, respectively. Different activated carbon electrodes were prepared from commercial activated carbon, tea waste activated carbon, rice husk activated carbon, and limmonia acidissma activated carbon. The CAC electrode was fabricated from commercial activated carbon and successfully applied in CDI for simultaneous electrosorptive treatment of Cr(VI) and fluoride binary feed. The different parameters optimization was carried out with CAC electrode. The optimized values of operating parameters were found as operating voltage 1.2 V, optimum feed flow rate 16 mL/min and pH above 7 were found best for simultaneous rejection of Cr(VI) and fluoride. All the optimized parameters were set for all further experiments. The result shows that maximum electrosorption capacity for Cr(VI) and fluoride were 0.85 mg/g and 0.82 mg/g for 10 mg/L; 3.67 mg/g and 3.22 mg/g for 100 mg/L Cr(VI) and fluoride binary feed, respectively at 1.2 V. Effective purification and regeneration of electrode were found for binary feed solution of Cr(VI) and fluoride. Similarly, other electrodes namely TWBAC electrode, RHAC electrode, LASAC electrode were successfully prepared from tea waste biomass activated carbon, rice husk activated carbon, limonia acidissima shells activated carbon respectively. The prepared electrodes were tested out in CDI application for simultaneous removal of Cr(VI) and fluoride. The TWBAC, RHAC, LASAC electrodes were found an effective removal performance at low concentration of feed. The percent removal of Cr(VI) and fluoride were found 88.5% and 85.20% for 10 mg L-1 mix feed solution respectively with TWBAC electrode. The percent removal of Cr(VI) and fluoride was found 83.1 % and 80.4 % for 10 mg L-1 mix feed solution respectively with RHAC electrode. The LASAC electrode was assembled in the MCDI system for simultaneous removal of Cr(VI) and fluoride from feed solution. The percent removal of Cr(VI) and fluoride came out to 92.2 % and 89.23% for 10 mg/L. In the present work, mono and multicomponent isotherm models were done. The Langmuir, Freundlich and Redlich Peterson isotherm models were used for the mono component system. The multicomponent isotherm models, namely modified Langmuir, non modified Langmuir, extended Langmuir, extended Freundlich, modified Redlich Peterson and non modified Redlich Peterson were used for multicomponent system. In isotherm study it was found that the removal of Cr(VI) and fluoride by CAC electrode follows Freundlich isotherm model and Redlich Peterson model was found to be best agreement for both Cr(VI) and fluoride in mono iv component models. Extended Freundlich model and Non modified R–P model among six applied multicomponent isotherm models were found to fit well with the experimental data for both Cr(VI) and fluoride electropsorption performance. The ion sorption process with TWBAC, RHAC and LASAC electrode follows Langmuir isotherm model and Redlich Peterson model for mono component; Extended Langmuir and Non modified Redlich Peterson for multicomponent isotherm modelling. A Kinetic model study was carried out for investigating the nature of sorption process. It is useful to find out equilibrium time and the mechanism of adsorption, such as physisorption and chemisorption. In kinetic study, it was found that Pseudo first order kinetic model is good agreement with experimental data for both Cr(VI) and fluoride by CAC, TWBAC, RHAC, and LASAC electrode. The sorption performance electrodes were found in the sequence as CAC electrode > LASAC electrode > TWBAC electrode > RHAC electrode. The maximum percent rejection of Cr(VI) and fluoride was found 94.35% and 80.1% with CAC electrode; 90.2 % and 76 % with LASAC electrode from industrial wastewater concentration [11 mg/L Cr(VI) and 35.24 mg/L fluoride ] respectively. Thus, membrane separation with NF300 and RO flat sheet membrane and CDI with CAC electrode and LASAC electrode could be a promising treatment for simultaneous electrosorptive removal of low concentrated Cr(VI) and fluoride from industrial wastewater.