UV/Photocatalyst based photoreactor design for water treatment

Abstract

A germicidal ultraviolet (UV-C)/photocatalyst based advanced oxidation process (AOP) has potential to disinfect and mineralize waterborne organic pollutants without generating disinfection by-products. But low efficiency has hindered application of this technology. In this study, I have looked to improve the AOP process through use of enhanced photocatalytic surfaces and reactor design. The intention is that the resulting improvements will help in combating the effects of water eutrophication due to global warming, which is often accompanied by accelerated cyanobacterial (blue-green algae) growth and waterway contamination by their toxins. An acidic anatase titanium dioxide (TiO2) slurry doped with tungsten oxide (WO3) or rutile TiO2 was coated onto stainless steel plates, and annealed at 460, 500, and 540°C in a muffled furnace. The coatings were ~10 µm thick and demonstrated good durability. This method enabled bandgap reduction to the visible light spectrum for all coatings, with the smallest bandgap being 2.48 eV. The higher annealing temperatures resulted in rougher coated surfaces, which had negative effect on photocatalytic activities. Methylene blue (MB) degradation tests under UV-C showed that the coatings annealed in 460°C had the best performance and with a rate constant of 5.59 h-1. An UV-C/TiO2 based photocatalytic reactor with a corrugated configuration was designed to accommodate a larger photocatalytic surface per unit volume. With TiO2 coated corrugated plates, a 70 % MB solution was degraded within the first 10 minutes with the highest photonic efficiency of 2.83 %. A light absorption model was developed and validated with light intensity measurements. A set of corrugated photocatalytic reactors with the same surface area, but different geometries were analyzed and the one with flatter configuration showed better energy absorption capacity. A household scale UV-C/TiO2 reactor was then designed for drinking water treatment. A 3D UV-C absorption model, that agreed well with light intensity measurements, was used to predict light energy absorbed by the photocatalyst coatings and to optimize reactor design. The system degraded a synthesized raw water pollutant (uracil) and the organic matter in lake water by 34.2 % and 33.2 % respectively in 24 minutes, and also concurrently inactivated Escherichia coli.