Powdered Activated Carbon Exacerbates Fouling in MBR Treating Olive Mill Wastewater

Noya Ran,Moshe Herzberg,Jack Gilron,Revital Sharon-Gojman

doi:10.3390/w11122498

Abstract

Membrane fouling is a major obstacle in membrane bioreactors (MBRs) that treat wastewater. The addition of powdered activated carbon (PAC) is commonly suggested as a way to improve the MBR wastewater treatment process with respect to membrane fouling and effluent quality. Integrating the PAC addition into the MBR may also improve the stability of the acclimated microbial community for biodegrading the recalcitrant organic compounds that can also enhance membrane fouling. In this study, the ability of the MBR-PAC system to decrease membrane fouling was evaluated. Two pilot-scale reactors were operated: one reactor was supplemented with suspended PAC, and one was operated under similar conditions, without PAC. The feed to the reactors comprised domestic and olive oil mill wastewater. Surprisingly, the permeate flux and the membrane permeability decreased faster in the MBR supplemented with PAC compared to the control reactor. Corroborating these MBR fouling results, soluble microbial products (SMPs), originating from the PAC-supplemented reactor, were found to be more adhesive to an ultrafiltration membrane mimetic surface (polyether sulfone) as analyzed in a quartz crystal microbalance with dissipation monitoring (QCM-D). While the PAC had almost no effect on the dissolved organic carbon in the MBR, it altered the molecular weight distribution of the organic molecules in the SMP as observed with gel permeation chromatography: The fractions of 577–789 kDa and the one bigger than 4 × 103 kDa, were elevated and reduced, respectively, by the addition of PAC. A biofilm formation analysis using a confocal laser scanning microscopy showed a higher amount of biofilm on the membrane taken from the PAC reactor, but this membrane showed no traces of PAC particles when analyzed with a scanning electron microscope (SEM). Taken together, altering the composition of the dissolved organic matter in the MBR by PAC addition promoted its adhesion to the membrane, induced biofilm formation, and more prominently, decreased membrane permeability.

Highlights

Membrane bioreactor (MBR) technology combines the microbial degradation of organic compounds and membrane separation [1]
It should be mentioned that the reduced permeate flux of the MBRs was affecting their refill rate by a water-level controlled valve fed with municipal wastewater with much lower DOC and BOD concentration than values of the oil mill wastewater (OMWW) feed to the MBRs
In which the powdered activated carbon (PAC) reactor performance was close to the control reactor and stabilized with lower VSS concentration (Table 1), we aimed at understanding the unexpected exacerbated fouling in MBR fed with PAC

Summary

Introduction

Membrane bioreactor (MBR) technology combines the microbial degradation of organic compounds and membrane separation [1]. Water 2019, 11, 2498 inorganic and microbial fouling (biofouling) and represents a major challenge to MBR operations [5]. The proliferation of microorganisms on the membrane commonly degrades membrane performance, as expressed by elevated specific energy consumption and more frequent backwash and chemical cleanings. An increased membrane cleaning frequency is required since the microorganisms survive even under stressed conditions, such as backwashing with different chemicals [6]. Several biofouling processes in ultrafiltration (UF) membranes in MBRs have been examined, including (i) adsorption of extracellular polymeric substances (EPS) to the membrane surface and pores,

Methods

Results

Conclusion