Abstract:

Due to recent changes in water quality regulations, including promulgation of the Long Term 2 Enhanced Surface Water Treatment Rule (LT2) and the Stage 2 Disinfectant and Disinfection Byproducts Rule (D/DBPR), water utilities may need to implement more extensive treatment to remain in full regulatory compliance.

Although low-pressure ultraviolet (UV) disinfection has been studied extensively, less is known regarding titanium dioxide photocatalysis for viral inactivation. In addition, the recent promulgation of the LT2 has justified research into alternative disinfection strategies for Cryptosporidium parvum. This study compares UV and photocatalytic inactivation with respect to four potential surrogate bacteriophages (MS2, PRD1, phi-X174, and fr), UV-resistant adenovirus (Ad4), three enteroviruses (poliovirus 1, coxsackievirus B6, and echovirus 12), and chlorine-resistant C. parvum. In addition, this study demonstrates the application of an integrated cell culture quantitative polymerase chain reaction (ICC-qPCR or ICC-qRTPCR) strategy for adenovirus and enterovirus disinfection studies. Using ICC-qPCR, the infectivity assay for adenovirus was reduced from two weeks to two days.

Using a bench-scale collimated beam apparatus and 1 mg/L of titanium dioxide, the setup achieved up to 20% and 60% reductions in the UV doses required for inactivation of the viruses and C. parvum, respectively. However, the collimated beam proved to be inefficient for photocatalysis at high titanium dioxide concentrations, which may be necessary for chemical destruction. The Photo-Cat Lab from Puri tics was used in the pilot-scale experiments. The pilot-scale experiments demonstrated rapid viral inactivation at an average rate of 0.17 kWh/cubic meter-log at high titanium dioxide concentrations (>100 mg/L) and significant physical removal by the ceramic membrane filter. Due to significant microbial adsorption onto the titanium dioxide in the pilot-scale experiments, it was not possible to completely evaluate the Photo-Cat Lab with respect to C. parvum. However, the submicron pore size of the ceramic membrane filter achieved 100% removal of C. parvum.

These results provide a proof-of-concept for both synergistic inactivation with low concentrations of titanium dioxide and rapid photocatalytic inactivation with high concentrations of titanium dioxide. This study substantiates further testing of simultaneous pathogen inactivation and chemical destruction using titanium dioxide photocatalysis in water treatment applications.