Design and Development of Photocatalytic Water Treatment Process for the Degradation of Wastewater Produced at Industrial Plants

Abstract

Waste water effluents from chemical industries contain toxic organic chemicals which are harmful for environment and bio-system. The need for environmental protection demands removal of such toxic contaminants from waste water prior to disposal. Titanium dioxide (TiO2) has become most suitable catalyst for the degradation of the waste water by using Photocatalytic Treatment. In the present study, Photocatalytic degradation has been studied for the removal of harmful and toxic pollutants from industrial waste water effluents. For this, the photocatalytic process was suitably modified in terms of design (catalyst form, different types of radiation source, and batch & flow mode) to have accelerated photo degradation for fast and complete removal of pollutants. In order to effectively utilize LEDs and UV light, this thesis investigates various types of photocatalysts like ZnO, TiO2 (Degussa P25) and metal ion-doped TiO2 for the treatment of waste water of the industrial plants. To reduce the COD of industrial effluents, batch experiments were conducted while determining the optimal operating conditions. Effect of experimental conditions such as pH, catalyst weight, light source etc. was studied under laboratory scale to make the reaction economically viable. The kinetic study was done by L H (Langmuir Hinshelwood) model of photocatalytic degradation. To develop the efficient and visible light active catalysts, TiO2 (Degussa P25) was doped with different metal such as Bi, Ag, and Ce etc. The effects of individual dopants on the COD degradation were compared with TiO2 (Degussa P25) by several reactions under UV light irradiation. In Doped TiO2 the calculated %COD reduction was obtained more than the undoped TiO2 (Degussa P25) in same time period. To carry out the reactions in the continuous flow reactors the catalyst particles were immobilized on glass plates by a dip coating method, so catalyst can be reused for several times. The photo degradation for COD removal was carried out using this system where in UV lamp (used as a light source) was kept into the quartz reactor and the contaminated waste water collected from industrial plant was circulated through the pump. For reuse, the same glass plates coated with TiO2 catalyst were used in reactor 3 times with same operating parameters and % loss of catalyst and extent of photo degradation (% COD removal) were than calculated. In first cycle approximately 70% COD removal was obtained in 10h as shown in graph in the second cycle the % COD removal was reduced to about 55-60% in 10 hrs. Further when the coated glass plates were used in third cycle the COD removal could be achieved only 40-45% in 10h.