Understanding and Overcoming Challenges to Photochemical Water Treatment Technologies

Photochemical water treatment technologies have been extensively studied in recent years to update the current practices and find an innovative, cheap, and sustainable way to treat contaminated water. Despite the well-documented advantages, these technologies faced some challenges and limitations in the way of technology transfer. Among all the challenges, the presence of dissolved organic matter (DOM) poses a serious challenge to the application of these technologies, especially photocatalysis. Moreover, the prospect of utilizing the new technology of light-emitting diodes (LEDs) offers an upgrade in the efficiency of the current practice of ultraviolet (UV) dosing. To understand the effect of DOM in photocatalysis, fractionated DOM samples were collected from a Membrane bioreactor (MBR). These samples provide a unique examination of the inhibitory effect of DOM in TiO2-mediated photocatalysis for degradation of a probe compound, para-chlorobenzoic acid (pCBA). The inhibitory effect was the strongest for colloidal fraction followed by transphilic and then the hydrophobic fractions. It was found the fouled membrane can filter the most problematic DOM fraction and decrease this inhibition while the recently cleaned membrane caused the greatest inhibition of photocatalysis. Manipulation of pH showed increasing pH mitigates the inhibition but increasing IS caused strong inhibition. The manipulation of IS could not change the inhibitory mode of HPO or TPI. Results showed the competition for adsorption on the surface not the aggregation of TiO2 is the key factor in the inhibition of photocatalysis. To explore the potential application of UV LEDs for disinfection application, the potential bacterial repair of Escherichia coli under irradiation of this type of light was studied under two conditions of dark repair and photoreactivation. Switching from UV254 to UV278 irradiation impacted the propensity for E. coli to repair under both dark and illuminated conditions and light intensity was particularly important. Dark repair showed less repair in UV278 than UV254, but in the photoreactivation when DOM was present E. coli recovered much more rapidly after irradiation with UV278. The susceptibility of E. coli to UVA was increased by prior exposure to UVC, with a larger effect from UV278