HETEROGENEOUS CATALYSIS FOR THE TREATMENT OF RESIN INDUSTRY WASTEWATER

Abstract

In recent decades, organic pollutants continuously discharged from industries have gained a high pace leading to enormous generation of wastewater. The contamination of surface and ground water caused by synthetic resins like acrylonitrile-butadiene-styrene (ABS) resin and nitrile rubber production are serious environmental problem. During the ABS resin production huge amount of wastewater generates and containing the highly toxic and refractory pollutants viz., acrylonitrile and their family compounds (3,3-imminodipropiononitrile and 3,3-oxydipropiononitrile), acrylic acid and acrylamide. Acrylonitrile and acrylamide both compounds are very highly toxic even at low concentration level, because they exhibit characteristics like neurotoxicity, mutagenicity, carcinogenic and reprotoxic nature. Acrylamide has been classified Group B2, probable potential human carcinogen by United States Environmental Protection Agency (USEPA) and acrylonitrile has been identified as the third rank most toxic pollutant in the 129 priority pollutants list. The chronic exposure of acrylamide leads to damage the central and nervous peripheral system and ataxia in legs and chronic exposure to acrylonitrile causes asphyxia, irritation to the respiratory system and digestive tract. In the present study, Authors have treated the synthetic aqueous solution of individual compounds (viz., acrylonitrile, acrylic acid and acrylamide), multicomponent solution as well as treated the real acrylonitrile butadiene styrene (ABS) resin wastewater by heterogeneous catalysis process with various synthesized catalysts (e.g., Perovskite-like catalysts, mixed oxides, and doped catalysts) and activated by various oxidants (viz., peroxymonosulfate (PMS) and hydrogen peroxide (H2O2)). Synthesized catalysts were characterized by various analytical techniques including XRD, FTIR, BET, FE-SEM with EDAX, TEM and XPS. Novel heterogeneous series Perovskite-like catalysts SrCuxNi1-x O3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1) were synthesized by citric solgel method and activated with peroxymonosulfate (PMS) for the degradation of highly toxic pollutants acrylonitrile (ACN) and acrylamide (ACM) from aqueous solution. Catalyst 0.6SCN exhibit the highest catalytic activity and maximum removal of acrylonitrile (96%) and acrylamide (81%) along with 86% PMS consumption were observed at optimum operating conditions. In addition, stability and recyclability of 0.6SCN catalyst were assessed and removal efficiency of acrylonitrile suppressed 6% and acrylamide suppressed 11% over the fourth cycle of experiments along with very low leaching of Cu and Ni were observed. Finally, the operating cost of treatment process was assessed $50.62/m3 of wastewater in 0.6SCN/PMS system. The other Perovskite-like catalysts La0.5Ce0.5MO3 (M= Fe, Cu and Co) synthesized by solgel method and activated with H2O2 for the degradation of acrylonitrile from aqueous solution. During catalytic peroxidation, influence of various operating parameters such as, catalyst dose (250–1250 mg/L), H2O2/acrylonitrile molar ratio (0.5–2.5), pH (2–10) and reaction temperature (30–90 °C) were studied and optimized through central composite design (CCD) in response surface methodology (RSM). The maximum removal of acrylonitrile at various concentrations viz., 100, 200, 300 and 500 mg/L were 90.11%, 77.56%, 71.62% and 60.37%, respectively at optimum operating conditions i.e., LCFe catalyst dose 660 mg/L, H2O2/acrylonitrile molar ratio 1.54, pH 5.4, reaction temperature 56.7 °C and reaction time 3 h. The acrylonitrile removal was gradually dropped from 90.11% to 80.38%, 73.42% and 69.92%, in second, third and fourth cycles, respectively. The operating cost of acrylonitrile treatment from aqueous solution was estimated to be $61.14/m3 wastewater by catalytic peroxidation process. In addition, other catalysts Ni doped ceria (0, 2.5, 5 and 7.5 wt.%) synthesized by co precipitation method and utilized for the treatment of acrylonitrile aqueous solution. Catalyst 2.5% Ni–CeO2 exhibited the highest catalytic activity for the treatment of acrylonitrile. The maximum removal of acrylonitrile was 91.56%, 89.70%, 86.59% and 84.12% for various concentrations of acrylonitrile 100, 200, 300 and 400 mg/L, respectively at optimum operating conditions (i.e., catalysts dosage 500 mg/L, pH 6.5, nickel loading 2.5 wt.%, H2O2/acrylonitrile molar ratio 1, and temperature 298 K). The real ABS resin wastewater was treated by series Perovskite-like catalysts LaCuxFe1-xO3 (x = 0.2, 0.4, 0.6, 0.8) synthesized by solgel method and activated with PMS. The maximum removal of acrylonitrile (94.06%) and TOC (66.70%) was observed with optimized catalyst LaCu0.6Fe0.4O3. Catalyst reusability and chemical stability study were performed and degradation of acrylonitrile i.e., 94.06%, 91.38%, 88.42% and 86.92%; and TOC i.e., 66.70%, 64.35%, 61.59% and 59.21% were observed in first, second, third and fourth consecutive cycles. Operating cost for the treatment of ABS resin wastewater was estimated to be 75.60 $/m3 wastewater. Heterogeneous catalysts M-Al2O3/SiO2 (M = Fe, Co and Ni) derived from fly ash was synthesized via wet impregnation method and utilized for the treatment of real ABS resin wastewater. Catalyst Fe-CFA exhibit the highest catalytic activity on H2O2 activation at optimum operating conditions obtained from CCD design in RSM tool (i.e., catalyst dose 899 mg/L, 18.02 H2O2 mM, pH 6.67, and reaction temperature 54.99 ◦C). The maximum removal of acrylonitrile (95.62%) and COD (88.95%) were obtained. The stability of catalyst Fe-CFA was fairly good over four cycles of experiments and very low metal leaching (Fe) i.e., 2.98 mg/L, 2.68 mg/L, 1.96 mg/L and 1.69 mg/L in 1st, 2nd, 3rd and 4th consecutive cycle were observed which are blow the standard discharge permissible limit by CBCB India. The overall operating cost of treatment process was estimated as 50.72$/m3 of ABS resin wastewater. The catalytic activity of La0.5Sr0.5BO3 (B=Cu, Fe and Ni) Perovskite-like catalysts synthesized by sol-gel method were examined for catalytic peroxidation of acrylic acid. The maximum degradation of acrylic acid 86.79%, 75.46% and 64.58%; and COD 71.57%, 68.23% and 59.35% were observed catalysis with LSCu, LSFe and LSNi, respectively at optimum operating conditions (e.g., catalyst dose 600 mg/L, stoichiometric molar ratio of H2O2/acrylic acid 1.5, pH 3 and temperature 65 °C). The maximum degradation of acrylic acid with optimized catalyst LSCu at various concentrations, 100, 200, 300 and 400 mg/ L were 86.79%, 81.21%, 78.98% and 73.02%, respectively at the same operating conditions.