Materials Science Forum Vol. 712

Abstract: Various organic amines, most of which both toxic and carcinogenic, are being used extensively worldwide in the syntheses of azo-dyes, polyurethane, pesticides, nylon and many other nitro-aromatics. However, the uncontrolled discharge of these products, back into the environment, releases many primary or intermediate products with similar or even worse levels of toxicity. Therefore, knowledge of the degradation and complete mineralization of these amines, using best techniques with optimum efficiency, is needed. This review is aimed at summarizing the existing studies used for the degradation of amines, employing techniques, such as; biodegradation, thermal, chemical, electrochemical, photochemical, photocatalytic, sonochemical, sono-photo catalytic and sono-ozonation processes. The reactor design for the large scale degradation with optimum efficacy has also been discussed besides attempting a structural correlation to save the environment from such chemical hazards.

Abstract: Among the new oxidation methods in advanced oxidation processes, heterogeneous photocatalysis based on UV/ titanium dioxide is one of the emerging technologies for degrading and totally mineralizing toxic and highly stable carboxylic acids from waste water has attracted great attention in last decade. The aliphatic and aromatic carboxylic acids are widely used as reactants or produced as main products or byproducts in various chemical process industries. These chemical process industries generates waste water containing significant amount of carboxylic acids, which need to be removed from waste water before disposal to natural water bodies due to the environmental restrictions and their hazardous effects on flora and fauna. This paper reviews photocatalytic degradation (PCD) process for various carboxylic acids in detail, including basic mechanism of titanium dioxide, effect of carboxylic acid structure and various reaction parameters like effect of initial concentration and kinetic study, catalyst loading, pH, adsorption and deactivation of the photocatalyst. A critical analysis of the available literature has been made and some general conclusions have been drawn related to the above mentioned parameters. The photocatalytic degradation pathways for carboxylic acids are also discussed to understand this process thoroughly.

Abstract: Development of photocatalysts and photoreactors for treatment of industrial effluents is considered important to harness solar energy for environmental clean up. The photocatalytic method of decolorization of textile dyes utilizes UV component of sunlight (3-5%) and the only solid phase (TiO₂ catalyst) can be recycled on a technical scale. Moreover, the method does not produce any sludge unlike adsorption and coagulation methods. These attributes of the photocatalytic method are attractive for possible application in industry. Our group is presently working on pilot scale photoreactors and exploring feasibility of industrial application of this technique. We have developed a few TiO₂ based photocatalysts (P-25 TiO₂, ZnO, TiO₂ (bulk) and rare earth metal (In₂O₃, Nd₂O₃, Yb₂O₃ and Sm₂O₃) doped TiO₂), photo catalyst bearing supports (e.g., acrylic sheet) and photoreactors (annular immersion well type, falling film type and shallow slurry photoreactors) for use with UV & sunlight. We have carried out a few tests with Solar Slurry Photoreactor (SSPR) in field using actual textile wastewater with encouraging results. The SSPR developed under this study was capable of decolorizing textile wastewater under specified conditions approximately with a treatment rate of 9.0 Lh^-1. The reactor area exposed to sunlight was approximately 1 m². Thus, a reactor having 18-20 m² exposed area would treat about 1.0 m³ textile wastewater at a rate approximately equal to180 Lh^-1. The present data suggest that it may be possible to apply this technique initially for the color treatment of textile wastewater from small dyeing operations. However, the details of techno-economic feasibility need to be assessed beforehand. The proposed book chapter would present details of all the above-mentioned efforts. It would be targeted to bring out inadequacies associated with the photocatalytic technology for wastewater treatment.