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In the present study, the photocatalytic degradation of 2,4,6-trichlorophenol (2,4,6-TCP) was carried out in a batch reactor under UV light in aqueous solution for 5 h using titania P-25 (surface area 50 m2/g) as a photocatalyst and sodium hypochlorite as an oxidant. Variables studied include catalyst dose (0.25–1.25 g/L), pH (2–6), and concentration of the oxidant (3.06 × 10-6M–15.3 × 10-6M). The rate of degradation was studied in terms of changes in concentration of the pollutant and reduction in chemical oxygen demand. The optimal values of operational parameters leading to 2,4,6-TCP abatement were obtained by using response surface methodology. The percent degradation and COD reduction of 2,4,6-TCP was found to increase with increases in the catalyst dose up to the dose of 1.1 g/L, pH in the range of 4–4.5, and oxidant concentration of 9.95 × 10-6M. [ABSTRACT FROM AUTHOR]

Abstract: The present study deals with the characterization and treatment of bleach plant effluents generated from Indian varieties of wheat straw or bagasse or hardwood/non wood materials. Spent bleach liquor (SBL) was generated by the chlorination and extraction of unbleached pulp under controlled conditions at laboratory scale. SBL as well as effluents collected from different pulp and paper mills were examined for various characteristics such as total solids (TS), total suspended solids (TSS), total dissolved solids (TDS), pH, chemical oxygen demand (COD), biological oxygen demand (BOD) and chloride ion concentration and their degradation was studied by heterogeneous photocatalytic systems using titanium dioxide (TiO2) and zinc oxide (ZnO) under UV/solar irradiation. The degradation of the organic matter present in the effluent was evaluated as COD removal and reduction in BOD. For the applicability of cost effective heterogeneous photocatalytic process at industrial scale, solar photocatalytic water detoxification was explored and satisfactory results were obtained. [Copyright &y& Elsevier]

The photocatalytic degradation of lignin obtained from wheat straw kraft digestion has been investigated by using TiO2 and ZnO semiconductors. ZnO has been found to be a better photocatalyst than TiO2. The different variables studied, include catalyst dose, solution pH, oxidant concentration and initial concentration of the substrate. The degradation of lignin was favorable at pH 11. Optimum values of catalyst dose and oxidant concentration were found to be 1g/l and 12.2×10−6 M, respectively. The degradation of the organic compound was also evaluated as COD removal and increase in the COD removal was observed with increase in degradation rate. An attempt has also been made to explore the applicability of ZnO in immobilized mode for the degradation of lignin under solar light for industrial scale application. Further the comparative evaluation of ZnO in slurry/immobilized mode has been carried out. [Copyright &y& Elsevier]

The present study involves the photocatalytic degradation of Methyl Orange (MO) and Rhodamine 6G (R6G), employing heterogeneous photocatalytic process. Photocatalytic activity of various semiconductors such as titanium dioxide (TiO2), zinc oxide (ZnO), stannic oxide (SnO2), zinc sulphide (ZnS) and cadmium sulphide (CdS) has been investigated. An attempt has been made to study the effect of process parameters viz. , amount of catalyst, concentration of dye and pH on photocatalytic degradation of MO and R6G. The experiments were carried out by irradiating the aqueous solutions of dyes containing photocatalysts with UV and solar light. The rate of decolorization was estimated from residual concentration spectrophotometrically. Similar experiments were carried out by varying pH (2–10), amount of catalyst (0. 25–2. 0g/l) and initial concentration of dye (5–200mg/l). The experimental results indicated that the maximum decolorization (more than 90%) of dyes occurred with ZnO catalyst and at basic pH and the maximum adsorption of MO was noticed at pH 4 and of R6G at pH 10. The percentage reduction of MO and R6G was estimated under UV/solar system and it was found that COD reduction takes place at a faster rate under solar light as compared to UV light. In case of R6G, highest decolorizing efficiency was achieved with lower dose of catalyst (0. 5g/l) than MO (1g/l) under similar conditions. The performance of photocatalytic system employing ZnO/solar light was observed to be better than ZnO/UV system. [Copyright &y& Elsevier]