Fixed Bed Photocatalysis for the Degradation of 2-Chloro 4-Nitrophenol Using Solar Irradiation

Abstract

Phenol and phenolic compounds occur as waste from various industries like Oil refining, petrochemical, coal mining, lignite transformation etc. and result in bioaccumulation. Water from natural sources is mainly polluted due to chemicals present in the wastewater let out from industries of various domains. High COD, opacity, high alkalinity/acidity, high total solids and high BOD are the characteristic of industrial wastewater. This creates an imbalance in the ecosystem and hence treatment of such wastewaters is needed. 2 chloro 4 nitro phenol (2-C 4-NP) is one among the mostly used phenolic compound. It is used as an intermediate in wood preservative, in the medical treatment of obesity, and also in a pesticide. An effective and economic treatment for eliminating phenolics in water has been in urgent demand. One method to remove 2-C 4-NP from the wastewater is fixed bed photocatalysis. Photocatalysis is a technique that uses solar radiation and a photocatalyst, the photon energy from sun is used for generating hydroxyl radicals formed as a result of oxidation of catalyst that remove organic matter in wastewater. TiO2 is one of the most popular and promising materials, because of its stability under harsh conditions, commercial availability, different allotropic forms with high photo-activity, possibility of coating as a thin film on solid support, ease of preparation in the laboratory etc. Its absorption spectrum overlaps with the solar spectrum and hence opens up the possibility of using solar energy as the source of irradiation. To eliminate the need of filter during post-treatment removal using suspended photocatalyst, researchers tested various catalyst supports.

The scope of the study is to see the heterogeneous photocatalytic degradation of 2-C 4-NP in TiO2 fixed bed reactor. For the process optimization like pH, Oxidant dose, initial concentration suspension mode photocatalysis. For the immobilization of catalyst three different supports (cemented beads, glass sheet and sodium alginate balls) are used. The degradation studies in slurry form are investigated using TiO2 Degussa photocatalysts under UV illumination. The study includes dark adsorption, UV light treatment along with variation in different parameters like pH, amount of photocatalyst, effect of H2O2 concentration. Degradation observed was 89%, 70%, 65% and 60% under suspension solar-photocatalytic, glass-plate solar reactor, coated cemented beads and immobilized sodium alginate ball; respectively at optimized conditions i.e. 4.5 pH, catalyst concentration of 1 g/l and oxidant dose of 7.5mM/200ml. The dip and coating method was used for the catalyst immobilization on the glass and cemented beads, whereas in other case, physical entrapment of the catalyst slurry in the gel was used. Approximately 95% reduction in COD confirms the mineralization of the compound under study. Result shows that fixed bed photocatalysis would be more efficient and economical as filtering as well as recovery of the catalyst can be avoided. The application of solar powered photocatalytic reactors to treat waste water from different industries holds promise for regions receiving strong sunlight throughout the year, such as India.