title: Synergistic effect of ultrasonic pre-treatment combined with UV irradiation for secondary effluent disinfection.
abstract: The ultraviolet (UV) disinfection efficiency is often affected by suspended solids (SS). Given their high concentration or large particle size, SS can scatter UV light and provide shielding for bacteria. Thus, ultrasound is often employed as a pre-treatment process to improve UV disinfection. This work investigated the synergistic effect of ultrasound combined with UV for secondary effluent disinfection. Bench-scale experiments were conducted in using samples obtained from secondary sedimentation tanks. These tanks belonged to three wastewater treatment plants in Beijing that use different kinds of biological treatment methods. Several parameters may contribute to the changes in the efficiency of ultrasound and UV disinfection. Thus, the frequency and energy density of ultrasound, as well as the SS, were investigated. Results demonstrated that samples which have relatively higher SS concentrations or higher percentages of larger particles have less disinfection efficiency using UV disinfection alone. However, the presence of ultrasound could improve the disinfection efficiency because it has synergistic effect. Changes in the particle size distribution and SS concentration notably affected the efficiency of UV disinfection. The efficiency of Escherichia coli elimination can be decreased by 1.2 log units as the SS concentration increases from 16.9 mg/l to 25.4 mg/l at a UV energy density of 40 mJ/cm(2). UV disinfection alone reduced the E. coli population by 3.4 log units. However, the synergistic disinfection of ultrasound and UV could reach 5.4 log units during the reduction of E. coli at a 40 kHz frequency and an energy density of 2.64 kJ/l. The additional synergistic effect is 1.1 log units.
authors.affiliation: School of Civil & Environmental Engineering, University of Science & Technology Beijing, Xueyuan Road 30, 100083 Beijing, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Jin
authors.forename: Zifu
authors.initials: Z
authors.lastname: Li
authors.forename: Lanlan
authors.initials: L
authors.lastname: Xie
authors.forename: Yuan
authors.initials: Y
authors.lastname: Zhao
authors.forename: Tingting
authors.initials: T
authors.lastname: Wang
mesh_terms: D004203:Disinfection; D004926:Escherichia coli / Q000528:radiation effects*; D010316:Particle Size; D014465:Ultrasonics; D014466:Ultraviolet Rays