OZONATION COMBINED WITH NANOFILTRATION AS A PATHBREAKING AND EFFECTIVE PROCEDURE IN TREATING DYE EFFLUENTS FROM TEXTILE INDUSTRIES WITH THE HELP OF A BUBBLE COLUMN-AN INSIGHTFUL REVIEW

摘要

Persistent chemicals in wastewater cannot be degraded by primary and secondary treatments. So the need of tertiary treatment processes such as ozonation. Primary treatment comprises flocculation and coagulation while secondary treatment comprises activated sludge process or filtration through trickling filters. Tertiary treatment process comprises ozonation, membrane filtration and adsorption. The importance of ozonation as an advanced oxidation process is due to the fact that ozonation process is environmental friendly and sound. Our review will delineate the research work done in the area of ozonation, primarily the ozonation of dye effluent in wastewater from textile industries. The ozone method is known to be effective for decomposing Organic chemicals containing carbon-carbon double bonds, olefenic double bonds, acetylenic triple bonds, aromatic compounds, phenols, polycyclic aromatics, heterocyclics, carbon-nitrogen double bonds, carbon-hydrogen bonds, silicon-hydrogen and carbon-metal bonds. Some visionary work has been done in the ozonation of reactive dyes in the wastewater effluent of textile industries. Synthetic dyes and pigments released to the environment in the form of effluents by textile, leather and printing-industries cause severe ecological damages. These dyes include several structural varieties of dyes such as acidic, reactive, basic, azo, diazo, anthraquinone based and metal complex dyes. Neither simple chemical nor biological treatment alone has proved adequate in decolorization and sufficient depletion of inorganic matter. Due to the inhibitory nature of many compounds for biological oxidation, the need for pretreatment by advanced oxidation process (AOP) has become essential. One of the AOP processes is ozonation, which is versatile and environmentally powerful. Ozonation of water is a well known technology and the strong oxidative properties of O3 and its ability to effectively oxidise many organic compounds in aqueous solution have been well documented. Ozone treatment of several types of wastewater has resulted in considerable COD reduction and has been used for treatment of dyes, phenols, pesticides etc. In recent years, ozonation is emerging as a potential process for color removal of dyes, since the chromophore groups with conjugated double bonds, which are responsible for colour can be broken down by ozone either directly or indirectly forming smaller molecules, thereby decreasing the colour of effluents. Due to its high electrochemical potential (2.08 V), O3 is the strongest oxidant available and applicable as compared to H2O2(1.78 V) and can react with several classes of compounds through direct or indirect reaction. Unlike other oxidising agents such as Cl,,oxidation with O. leaves no toxic residues that have to be removed or disposed. Studies carried out by several scientists show that ozone generally produces non-toxic end products which are converted to CO2 and H2O depending on the conditions. Nanofiltration is very effective and the next generation science and technology. Our aim, objective and vision is to delineate the major research work done in the field of ozonation in order to project it as a powerful advanced oxidation process and also describe significant work done in the field of nanofiltration of dyes.