Zinc oxide photocatalytic decolourization of black tea (camellia sinensis) wastewater from processing factories in Kenya

Abstract

Decolourization of persistent brick-red colour of black tea processing wastewater was investigated. Wastewater samples were collected from three black tea processing factories in the western Kenya tea growing highlands and were subjected to photocatalytic reaction on zinc oxide semi-conductor. An amount of 500 cm3 of wastewater was put in the photocatalytic reactor with a floor coated with a thin layer of ZnO to give a water height of cca 2 cm. a. This was illuminated with artificial UV lamp producing radiation at wavelength 365 nm of intensity 3.0 mW/cm2for 3 hrs. A second set of experiments was carried out using solar light of intensity 1.4mW/cm2. Samples of 5 cm3 were drawn every 15 minutes and analyzed using UV/Vis spectrophotometer at ?=410 nm. A total of 48 analytes showed decolourization of 77% - 87% of the brick-red colour in 3 hrs. Solar illumination produced higher efficiency of decolourization of 3% above UV lamp. On average decolourization of 61% solar and 58% UV lamp was achieved in 60 minutes although solar radiation intensity was less than half that of UV lamp.