A Novel Model of Pressure Decay in Pressure-Driven Membrane Integrity Tests Based on the Bubble Dynamic Process

Junfeng Wu,Pengchao Xie,Jiaqi Ding,Han Xu,Songlin Wang,Wenxin Xu

doi:10.3390/app9020273

Abstract

The membrane integrity is estimated using a pressure decay test based on the bubble dynamic process of membrane defects. The present work builds a schematic diagram for a bubble formation model of a pressure decay test, proposes a simulation model of pressure decay rate (PDR) in the membrane gas chamber by means of numerical simulation using microdefect bubble dynamic behavior, and tries to establish the main factors influencing the back-calculated defect size resolution. Results obtained from the variations in the membrane gas chamber pressure and the PDR allowed for accurate determination of the membrane defect size, and the PDR was found to be relatively dependent on the gas chamber volume and the initial applied test pressure. The measured data about PDR using controlled experimental parameters was in good agreement with the trend found in the prediction model, proving that the pressure decay test process is in essence a bubble dynamic process. Furthermore, the back-calculated defect size resolution was found to decrease with the increase in gas chamber volume and PDR as well as with the decrease in applied pressure.

Highlights

Intact, low-pressure ultrafiltration membranes can completely remove particulates and pathogens and produce drinking water that meets the stringent regulations on water quality [1]
By means of numerical simulation using microdefect bubble dynamic behavior, the present work proposes a prediction model of pressure decay rate caused by membrane defects using the pressure decay test
The measured data for the pressure decay rate (PDR) using controlled experimental parameters, such as defect size, gas chamber volume, applied initial test pressure, and water depth, was found to be in good agreement with the trend followed by the prediction model

Summary

Introduction

Low-pressure ultrafiltration membranes can completely remove particulates and pathogens and produce drinking water that meets the stringent regulations on water quality [1]. Integrity tests should be sensitive to defects as small as 3 μm, which is based on the lower size range of Cryptosporidium oocysts, so that the tests can make sure any defect that is large enough for oocysts to pass will prompt a response from the integrity test being used [1,3,4]. In such a context, the detection method should be highly sensitive, quick and easy, have a signal that can be interpreted by programmable logic controller (PCL), and should be able to be carried out as frequently as possible. The generic protocol for a pressure decay test described in the United States Environmental Protection Agency (USEPA) guidelines is as follows: (1) drain the

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