The present study evaluated inactivation efficiency of a sonophotocatalytic process using ZnO nanofluids including ultrasonic parameters such as power density, frequency and time. The result showed that inactivation efficiency was increased by 20% when ultrasonic irradiation was combined with photocatalytic process in the presence of natural light. Comparison of inactivation efficiency in photocatalytic, ultrasonic and sonocatalytic processes using Escherichia coli as a model bacteria identified that inactivation efficiencies are shown in the following order: ultrasonic irradiation < sonocatalysis < photocatalysis < sonophotocatalysis. Furthermore, inactivation mechanism of sonophotocatalysis was proposed. Studies of reactive oxygen species (ROS) and zinc ions (Zn²⁺) release evaluation revealed that ROS play a key role in bacterial inactivation rather than Zn²⁺. Permeability of outer membrane (OM) and inner membrane (IM) of E. coli bacterial cells were studied and exhibited that sonophotocatalysis increased the permeability of OM and IM significantly. The enhanced bacterial inactivation effect in sonophotocatalytic process contributed to acoustic cavitation, sonocatalysis of ZnO and sonoporation phenomenon.
© 2016 Elsevier B.V.

Due to the rapid elevation of health standards and the limited water resources, decontamination and disinfection have become a challenging aspect of water/wastewater treatment. Traditional disinfection in water/wastewater treatment is associated with limitations, such as the production of toxic disinfection by-products. With the development of nanofluids, there is more and more interest in using nanofluids in environmental sectors, especially in water/wastewater treatment. Nanofluids are not strong oxidants and are not expected to produce harmful disinfection by-products. Nanofluids exhibit good disinfection properties against a wide range of bacteria, including Gram-negative, Gram-positive and spore bacteria. Several patents disclose the typically used types of nanofluids and their possible disinfection/ decontamination mechanisms. The use of different nanofluids and their applications in different water/wastewater treatment have also been reviewed in this paper. © 2013 Bentham Science Publishers.

This work investigates the disinfection property of ZnO nanofluids, focusing on H2O2 production and the disinfection activities of ZnO suspensions with different particles/aggregates. The possible disinfection mechanisms of ZnO suspensions are analysed. In this work, a medium mill was used to produce ZnO suspensions with different sizes of particles/aggregates. During the milling process, five ZnO suspension samples (A-E) were produced. X-ray Diffraction (XRD) and Dynamic Light Scattering (DLS) analyses revealed that after milling, the size of ZnO particles/aggregates in the suspensions decreased. Disinfection tests, H2O2 detection assays and fluorescent analyses were used to explore the disinfection activities and mechanism of ZnO suspensions. Disinfection tests results showed that all the produced ZnO suspension exhibited disinfection activity against Escherichia coli. ZnO suspensions with smaller particles/aggregates showed better disinfection activities. The presence of H2O2 in ZnO suspension was analysed. The H2O2 detection assay suggested that there is 1μM H2O2 in 0.2g/l ZnO Sample A, while there was no H2O2 present in ZnO Sample E. Though results showed that there was no H2O2 present in ZnO Sample E, Sample E with a size of 93nm showed the best disinfection activities. Fluorescence tests detected that the interaction between E. coli lipid vesicles and ZnO Sample E was much faster and more efficient. This study firstly demonstrated that ZnO suspensions with different particles/aggregates produced different amount of H2O2. Results suggested that H2O2 is responsible for the disinfection activity of larger ZnO particles/aggregates while the interaction between smaller ZnO particles/aggregates and vesicle lipids is responsible for the disinfection activity of smaller ZnO particles/aggregates. © 2013.

This work investigates the disinfection property of ZnO nanofluids, focusing on H2O2 production and the disinfection activities of ZnO suspensions with different particles/aggregates. The possible disinfection mechanisms of ZnO suspensions are analysed. In this work, a medium mill was used to produce ZnO suspensions with different sizes of particles/aggregates. During the milling process, five ZnO suspension samples (A E) were produced. X-ray Diffraction (XRD) and Dynamic Light Scattering (DLS) analyses revealed that after milling, the size of ZnO particles/aggregates in the suspensions decreased. Disinfection tests, H2O2 detection assays and fluorescent analyses were used to explore the disinfection activities and mechanism of ZnO suspensions. Disinfection tests results showed that all the produced ZnO suspension exhibited disinfection activity against Escherichia coli. ZnO suspensions with smaller particles/aggregates showed better disinfection activities. The presence of H2O2 in ZnO suspension was analysed. The H2O2 detection assay suggested that there is 1 mu M H2O2 in 0.2 g/l ZnO Sample A, while there was no H2O2 present in ZnO Sample E. Though results showed that there was no H2O2 present in ZnO Sample E, Sample E with a size of 93 nm showed the best disinfection activities. Fluorescence tests detected that the interaction between E. coli lipid vesicles and ZnO Sample E was much faster and more efficient. This study firstly demonstrated that ZnO suspensions with different particles/aggregates produced different amount of H2O2. Results suggested that H2O2 is responsible for the disinfection activity of larger ZnO particles/aggregates while the interaction between smaller ZnO particles/aggregates and vesicle lipids is responsible for the disinfection activity of smaller ZnO particles/aggregates. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.