Critical Flux and Fouling Analysis of PVDF-Mixed Matrix Membranes for Reclamation of Refinery-Produced Wastewater: Effect of Mixed Liquor Suspended Solids Concentration and Aeration.

Ahmad Fauzi Ismail,Mohd Hafiz Dzarfan Othman,Mohammad Mahdi A Shirazi,Erna Yuliwati

doi:10.3390/membranes12020161

Ahmad Fauzi Ismail, Mohd Hafiz Dzarfan Othman + Show 2 more

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https://doi.org/10.3390/membranes12020161

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Abstract

Fouling tends to cause a significant increase in hydraulic resistance, decreased permeate flux, or increased transmembrane pressure (TMP) when a process is operated under constant TMP or constant flux conditions. To control membrane fouling and maintain sustainable operation, the concept of critical flux has been discussed by several researchers. Various fouling mechanisms, such as macromolecule adsorption, pore plugging, or cake build-up, as well as hydrodynamic conditions, for example aeration, can take place at the membrane surface. This study aimed to investigate the effects of mixed liquor suspended solid (MLSS) concentration and air bubble flow rate (ABFR) on the critical flux and fouling behavior, when treating refinery-produced wastewater. To determine the critical flux values, the experimental flux-steps were the following: (1) the filtration began with a 30 min step duration at a low flux (10 to 20 L/m2h); (2) at the end of this step (after 30 min), the permeate flux was increased, (3) this step was repeated until the TMP did not remain constant at the constant permeate flux, (4) the critical flux was then achieved. A critical flux model with an R2 of 0.9 was, therefore, derived, which indicates that the particle properties were regulated by the suspended solids. The increase of MLSS concentration, from 3 mg/L to 4.5 mg/L, resulted in a decrease of the permeate flux by 18%. Moreover, an increase in ABFR, from 1.2 mL/min to 2.4 mL/min, increased the permeate flux, but this decreased with a greater flow rate of aeration. To assess the stability and reversibility of fouling during critical flux (Jc) determination using a mixed matrix membrane, flux-step methods were utilized. A step height of 14.3 L/m2h and 30 min duration were arbitrarily chosen. The flux increased to 32.5 L/m2h with a slight increase of trans membrane pressure (TMP), while the rate of increase became significant at a higher flux of 143.6 L/m2h, due to fouling. Overall, this study proved that the response of MLSS concentration and aeration affected the membrane performance, based on the critical flux and fouling behavior.

Highlights

Membrane applications have been increasingly used in wastewater filtration, due to their promise for handling water scarcity
A fouling layer is composed of suspended solids; inorganic and organic complexes formed on the membrane surface
Fouling tends to cause a significant increase in hydraulic resistance, decrease the permeate flux, and enhance the transmembrane pressure (TMP), when the process is operated under constant TMP or constant flux conditions

Summary

Introduction

Membrane applications have been increasingly used in wastewater filtration, due to their promise for handling water scarcity. Preventing or reducing the formation of this fouling layer by using the critical flux concept, or making the layer formation reversible, could enhance the performance of the membrane processes. The reversibility of the fouling layer, as well as the critical flux of suspensions, appear to be dependent on hydrodynamic conditions and physicochemical properties [2,3]. To control membrane fouling and maintain sustainable operation, the concept of critical flux was first introduced in 1995 by Field et al [5]. Three major approaches can be identified to a specific membrane process, due to the complexities of the fouling phenomena. These are hydrodynamic (changing flow regime across the membrane surface), surface modification (changing the surface or foulant affinity), and regular cleaning

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