Practical insights into ultrasound-assisted heterogeneous Fenton membrane reactors for water treatment

Abstract

Cavitation damage to membranes is a major barrier for developing an ultrasound (US)-assisted membrane water treatment process. In this study, US was integrated to a heterogeneous Fenton membrane reactor for the treatment of pharmaceutical-containing water with the aims of i) fouling control, ii) enhancement of heterogeneous Fenton oxidation. In order to prevent membrane damages due to cavitation, the stable and violent cavitation regions were identified by quantification and analysis of the cavitation activity axial along the ultrasound transducer via hydrophone measurements. Results showed the cavitation activities occur in both regions with US on, while the cavitation damage to membrane materials was only observed when membranes were placed in the violent cavitation region. On one hand, cracking and physical erosion of the surface were observed on membrane samples when exposed to violent cavitation. On the other hand, no such erosion occurred in stable cavitation regions, and membranes kept their mechanical, chemical and morphological properties, confirming that cavitation damage was controlled by placing membranes in the identified stable cavitation region. Based on these results, a heterogeneous Sono-Fenton membrane reactor was designed by placing a scalable hollow-fibre membrane module in the stable cavitation region. Within this reactor, the experiments confirmed that the oxidation of organics was enhanced thanks to the US assistance in the novel designed heterogeneous Sono-Fenton membrane reactor. However, this study also showed that US accelerated membrane ageing and zeolite-catalysts erosion, leading to more severe fouling. Overall, this paper introduces a method to control the cavitation damage to membranes and discusses the issues in US-assisted membrane systems with practical insights.