Ultrasonic irradiation control of silica fouling during membrane distillation process

Abstract

• Ultrasonic irradiation was introduced into membrane distillation process.• Influence of ultrasonic irradiation on silica fouling control was investigated.• Calcium ion would destroy silica colloid stability and aggravate membrane fouling.• Ultrasonic irradiation can mitigate silica fouling and maintain permeate flux. a b s t r a c t a r t i c l e i n f o Ultrasonic irradiation was introduced into membrane distillation process and the influence of ultrasonic irradiation on silica fouling control was investigated. A gradual decline of permeate flux during the concentration process of silica solution was observed due to the formation and deposition of colloidal polysilicic acid on the membrane surface. The PTFE hollow fiber membrane could maintain its mechanical properties and initial pore size distribution in the presence of ultrasonic irradiation. Ultrasonic wave brought significant mechanical and thermal effects, and generated powerful shock wave and microstreaming with high speed. The microstreaming, shock wave and acoustic vortex streaming stimulated the liquid-membrane interface continuously, therefore the membrane surface could be effectively kept clean and the permeate flux was hardly affected by the increasing of concentration factor. Due to the charge neutralization and compression of double charged layer induced by calcium ions, the silica colloid stability was eliminated and the colloids aggregated. A large amount of silica scaling was deposited on the membrane surface even at the beginning of concentration process. With ultrasonic irradiation, the permeate flux maintained stable and was enhanced by about 43%; the ultrasonic irradiation could effectively control silica fouling during membrane distillation.

Ultrasound-assisted membrane technologies for fouling control and performance improvement: A review

“…Therefore, to improve the permeate flux of the DCMD and reduce fouling on the membrane surface, it is suggested to integrate DCMD with US technology, as shown in Figure 9. Several researchers focused on integrating DCMD with the US to overcome membrane fouling and improve the permeate flux [38,59,182,183]. Hou et al [182] designed and tested four transducers located outside the water bath to treat three different synthetic water samples containing CaSO4, CaCO3, and SiO2.…”

“…The detailed definition of terminologies used in ultrasound field and the parameters affecting its throughput will be discussed in the following section. US was integrated successfully with pressure-driven membrane separation [32][33][34][35][36] and emerging technology such as MD [37][38][39][40][41][42] to remove foulants from the membrane surface. The US-assisted membrane processes can significantly improve membrane performance.…”

A Mini Review on Antiwetting Studies in Membrane Distillation for Textile Wastewater Treatment

“…Compared with the sharp decline of flux in desalting the RO concentrate by DCMD, only 20% of permeation flux was observed within 300 h running after the implementation of the APS treatment. In another study, ultrasonication was integrated with the MD process to mitigate PTFE membrane scaling [98]. Specially, the membrane module was immersed vertically in an ultrasonic bath equipped with transducers, which could provide an ultrasonication of 20 kHz (frequency) and 260 W (acoustic power).…”

The use of ultrasound to mitigate membrane fouling in desalination and water treatment

“…In a study by Hou et al [109] on direct contact MD, the ratio of flux to initial flux was maintained at 93% and 97% in case of calcium sulfate and silica fouling, respectively, due to the shock waves and microstreaming produced by the ultrasound. In addition, ultrasound can also enhance the flux by reducing the temperature polarization in the MD process [111,112].…”