| dc.description.abstract | Wastewater from black tea (Camellia sinensis) processing factories is characterized by a persistent brown colour that conventional treatment works are unable to remove. In this work photocatalytic decolourization of persistent brick-red colour of black tea processing wastewater was investigated. Forty eight wastewater samples each of 500 cm3 were collected from three black tea processing factories in the western Kenya highlands, and subjected to treatment by Titanium dioxide and Zinc oxide photocatalysts. Wastewater physico-chemical parameters were determined by analyzing Total Organic Carbon, Chemical Oxygen Demand, Turbidity, Total Suspended Solids and Total Dissolved Solids levels. Total Organic Carbon concentration was determined using the direct method, where 30% sodium persulfate, oxidizes dissolved organic carbon to carbon dioxide. The carbon present, is proportional to concentration of carbonaceous material present. Chemical Oxygen Demand was determined by closed reflux titrimetric method measuring chromates calorimetrically. Untreated wastewater samples were analysed for total metals of Mn, Al, Fe and Ni levels by Atomic Absorption Spectroscopy equipped with a deuterium background correction and air-acetylene burner. Total Al metal was analysed using a nitrous oxide-acetylene burner. The results obtained indicate concentrations levels Fe=1.46 mg/L; Mn=1.17 mg/L; Al=18.89 mg/L and Ni=0.32 mg/L. Sample concentration ranged between 0.26 – 18.89 mg/L. A GC-MS analysis of untreated samples indicated the presence of organic macromolecules that were identifiable and quantifiable. The number of molecules were as follows; (CBH= 9, KBH=14 and NBH= 12) respectively. An amount of 500 cm3 of each wastewater sample was put in a photocatalytic reactor with a floor coated with a thin layer of ZnO to give a wastewater liquid height of approximately 2 cm. This was illuminated with Ultra violet lamps at 365 nm wavelength of intensity 3.0 mW/cm2 for 180 mins, and solar light of intensity 1.4 mW/cm2. Samples of 5 cm3 were drawn every 15 minutes and analyzed using Ultra Violet/Visible spectrophotometer at λ = 410 nm. These experiments were repeated using TiO2 coated floors. ZnO results indicate decolourization of 77% - 87% of the wastewater in 180 mins. Solar illumination produced higher efficiency of decolourization of 3% above Ultra violet lamp. On average decolourization of 61% solar illumination and 58% Ultra violet lamp was achieved in 60 minutes. Solar illumination intensity was 47% that of Ultra violet lamp.TiO2 results indicate that decolourization of 70.4% - 78.5% of the wastewater was achieved in 180 mins. Solar illumination produced higher efficiency of 2.3% above Ultra violet lamp irradiation. Decolourization of 59.7% solar and 54.4 % Ultra violet lamp was achieved in the first 60 minutes Solar radiation intensity used was 47% that of Ultra violet lamp for both photocatalytic systems. ZnO and TiO2 photocatalysts were characterized by Laser Induced Breakdown Spectroscopy, X-ray Diffraction, Scanning Electron Microscope, Energy Dispersive X-Ray Spectroscopy, and surface area measurements. Laser Induced Breakdown Spectroscopy analysis revealed discrete atomic lines, indicating Ti and Zn spectral peaks at λ = 400 nm, X-Ray Diffraction/Scanning Electron Microscope analysis showed particle sizes of ZnO of 16.21 nm ± 2 nm and TiO2 of 16.00 nm ± 2 nm and spherical in morphology, Energy Dispersive X-Ray Spectroscopy showed active catalyst element present 61.5%, Zn in ZnO and 61%, Ti in TiO2 and specific surface area of 40.14 m2/g ZnO and 31.76 m2/g TiO2. After 180 mins, Total Organic Carbon, Chemical Oxygen Demand, Turbidity, Total Suspended Solids and Total Dissolved Solids levels decreased by 74.8%, 58.5%, 45.1, 58.01% and 41.52% respectively but pH increased from acidity towards neutrality from 5.8 to 6.7. Treatment by Solar/Ultraviolet/ZnO system, indicated a 9.7% efficiency compared to Solar/Ultraviolet/TiO2 system. | en_US |
