Wastewater Disinfection with Peracetic Acid (PAA), UV Irradiation and Combined PAA-UV Treatments

Both UV irradiation and peracetic acid (PAA) are strong and proven disinfectants. In this study, we have investigated the potential synergistic effect of combined PAA and UV irradiation treatments for wastewater disinfection. Initial benchtop studies were followed by a side-stream pilot study to investigate the effect of both PAA and UV irradiation individually or together in combination. In the benchtop studies, the final effluent samples were split into three parts. The first part was treated with various doses of PAA ranging from 1.0 to 5 ppm. The second part was exposed to 10 mJ/cm2 dose of UV and the final or third part of effluent was first treated with 1-5 ppm doses of PAA followed by 10 mJ/cm2 of UV irradiation. Both benchtop and side-stream pilot studies found that pre-treatment of effluent with PAA significantly increased the disinfection efficiency of UV. Without PAA pre-treatment, 10 mJ/cm2 UV dose achieved a 2.0 log reduction in fecal coliform and E. coli in the benchtop studies. With PAA pre-treatment, and 10 mJ/cm2 UV irradiation, a 3.5 log reduction was achieved with 5 ppm and 5 minute contact time. Similar pattern was observed in the pilot study in which UV’s disinfection efficiency significantly increased after pretreatment of effluent with low dose of PAA. These data suggest that the PAA/UV sequential treatment is more effective than the UV or PAA treatments separately. This strategy can be used to significantly lower the disinfection dose of UV irradiation which in turn can save the utility financial resources in the form of reduced energy needs.