| Clean and safe water is the second essential constituent after air and its availability seems challenging due to the excessive growth in population, spontaneous urbanization, rapid industrialization and amateurish utilization of water resources. The problem of water pollution is highly alarming as already1.1billion people around the globe have no access to clean drinking water and around2.5billion are using contaminated water. To solve this problem, numerous conventional and even advanced treatments systems were applied for wastewater treatment. However, due to the complex chemistry of wastewater, none of these techniques is efficient enough to bring water up to legally acceptable level from refractory organic pollutants. The natural abundant availability, non toxic nature, activation ability for H2O2and buffer capacity are the attractive properties of bicarbonate application in wastewater treatment system. In this dissertation, we applied bicarbonate activation of hydrogen peroxide (BAP) concept and mainly focused on getting improvements both in stability as well in efficiency which are considered the major failure of already practiced treatment systems. Both these two parameters (efficiency and stability) were deeply evaluated on chlorophenols and dyes degradation both on bench level as well in the fixed bed reactor. The findings as bicarbonate not only improve the efficiency but also provide stability for supported catalysts, are thus highly encouraging in the development of green, efficient and sustainable treatment system.In the2nd chapter of this dissertation, the work demonstrates the degradation of4-chlorophenol,2,4-dichlorophenol,2,4,6-trichlorophenol and phenol as model compounds using bicarbonate-activated H2O2oxidation system in the presence of supported catalysts. The catalytic activity of catalyst was investigated in term of degradation of target compounds, Chemical oxygen demand (COD) and Total organic carbon (TOC) removals both for batch mode as well as in fixed bed reactor using CoMgAl-HTs and CoMgAl-SHTs, respectively. The leaching of cobalt ion was efficiently prohibited due to the presence of a weakly basic media provided by bicarbonate, and the CoMgAl-SHTs catalyst was found to retain its stability and good catalytic activity in fixed bed reactor for over300h. Extensive chemical probing, fluorescence and EPR studies were conducted to identify the actual reactive species in degradation pathway, which revealed that the reaction proceeds through generation of superoxide, hydroxyl radical along with carbonate radical.In the third chapter, a series of Co-Mg/AL ternary layered double hydroxide (LDH) catalysts with fixed Mg/Al ratio were prepared by co-precipitation method. The effect of Co on the activity of the catalyst was monitored on the degradation of methylene blue (MO) as model compound at batch level using bicarbonate activation of H2O2(BAP) system. On bench level, the best CoMgAl-4catalyst can completely decolorize both methylene blue (MB) and methylene orange (MO) in short time. In fixed bed reactor, the catalyst was found stable for over300h with nearly100%decolorization and over60%removal of chemical oxygen demand (COD) for initial150h which slowly dropped to46%even after300h. Similarly the TOC removal was found64%for initial30h which dropped to44%after300h. No leaching of Co was detected for the entire fixed experiment which may be accounted for long life stability and good activity of the catalyst. The formation of superoxide and hydroxyl radical as reactive oxygen species (ROS) were proposed by radical’s scavenger’s studies.The4th chapter presents the promotion of catalyst properties (CoMgAl) by impregnation of Cu through hydrothermal method. The impregnation of Cu synergistically improved both the stability as well as catalytic activity. The improved activity was accounted for catalyst stability (by minimizing leaching) and the fast reconstruction of the active phases through redox cycle. The catalyst was found highly reactive as it can degrade200ppm CP in less than40min while300ppm CP can be degraded in1h reaction time. Similarly,84%of COD and78%of TOC removal was noted for200ppm CP solution while for the other controlled catalysts both TOC and COD removal was significantly low. The catalyst showed complete stability during continuous reaction with high dose (1000ppm), where the entire CP was removed smoothly in5h without incremental increase in catalyst leaching for9h. The presence of·OH and·O2-was suggested as sole reactive species involved in the degradation of CP. |
PDF Full Text Request