Article

Relation between EPS adherence, viscoelastic properties, and MBR operation: Biofouling study with QCM-D

Ben Gurion University of the Negev, Zuckerberg Institute for Water Research, Sede Boqer Campus, Midreshet Ben Gurion, 84990, Israel.
Water Research (Impact Factor: 5.32). 12/2011; 45(19):6430-40. DOI: 10.1016/j.watres.2011.09.038
Source: PubMed

ABSTRACT Membrane fouling is one of the main constraints of the wide use of membrane bioreactor (MBR) technology. The biomass in MBR systems includes extracellular polymeric substances (EPS), metabolic products of active microbial secretion that adversely affect the membrane performance. Solids retention time (SRT) in the MBR is one of the most important parameters affecting membrane fouling in MBR systems, where fouling is minimized at optimal SRT. Among the operating parameters in MBR systems, SRT is known to strongly influence the ratio of proteins to polysaccharides in the EPS matrix. In this study, we have direct evidence for changes in EPS adherence and viscoelastic properties due to changes in the sludge removal rate that strongly correlate with the membrane fouling rate and EPS composition. EPS were extracted from a UF membrane in a hybrid growth MBR operated at sludge removal rates of 59, 35.4, 17.7, and 5.9 L day(-1) (corresponding SRT of 3, 5, 10, and 30 days, respectively). The EPS adherence and adsorption kinetics were carried out in a quartz crystal microbalance with dissipation monitoring (QCM-D) technology in several adsorption measurements to a gold sensor coated with Polyvinylidene Fluoride (PVDF). EPS adsorption to the sensor surface is characterized by a decrease of the oscillation frequency and an increase in the dissipation energy of the sensor during parallel flow of aqueous media, supplemented with EPS, above the sensor surface. The results from these experiments were further modeled using the Voigt based model, in which the thickness, shear modulus, and shear viscosity values of the adsorbed EPS layers on the PVDF crystal were calculated. The observations in the QCM-D suggested that the elevated fouling of the UF membrane is due to higher adherence of the EPS as well as reduction in viscosity and elasticity of the EPS adsorbed layer and elevation of the EPS fluidity. These results corroborate with confocal laser scanning microscopy (CLSM) image analysis showing thicker EPS in close proximity to the membrane surface operated at reactor conditions which induced more fouling at elevated sludge removal rates.

12 Bookmarks
 · 
439 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A submerged membrane bioreactor (MBR) treating synthetic wastewater was continuously operated to investigate the impacts of floc size on membrane fouling. Particle size distribution (PSD) analysis showed that almost all the sludge flocs in sludge suspension had size larger than 1 μm, which corresponded to low pore clogging fouling. Thermodynamic analyses showed that adhesion of sludge flocs on membrane surface needed to overcome a repulsive energy barrier. Decrease in floc size slightly increased the specific energy barrier, but highly increased the attractive specific interaction energy in contact, and as whole, facilitated adhesion of small flocs to the membrane surface. Presence of biopolymer matters in sludge suspension remarkably gave rise to the cake resistance. This result could be explained by the osmotic pressure mechanism. Decrease in floc size would greatly increase both of hydraulic cake resistance and osmotic pressure-induced resistance. The findings shed significant light on membrane fouling control.
    Chemical Engineering Journal 02/2015; 269. DOI:10.1016/j.cej.2015.02.002 · 4.06 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ultrasonication has been widely used for bound extracellular polymeric substance (EPS) extraction. However, the used ultrasonic power density is quite different in literature, which makes their results non-comparable. In this study, the effects of different ultrasonic power densities on extracting bound EPS were assessed via analyzing carbohydrates, proteins, humic acids and DNA. Experimental results proved that ultrasonication power density had a significant effect on loosely bound EPS (LB-EPS) extraction, and an appropriate power density termed critical power density was found to be 35 W/10 mL according to the variations of DNA which represented the intactness or damage of cell membrane. Nevertheless, carbohydrates, proteins and humic acids did not change obviously in tightly bound EPS (TB-EPS) until a very high power density was applied. The critical power density was determined as 65 W/10 mL for TB-EPS extraction. The results indicated that a critical power density should be used in order to extract maximal EPS but not to damage cell membrane intactness.
    Desalination 11/2013; 329:35-40. DOI:10.1016/j.desal.2013.09.002 · 3.96 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The rheological properties of membrane biofouling layers developing in Membrane Bioreactors (MBR) have not been measured directly so far, although they are essential for understanding biofouling and for determining conditions to mitigate it. The development of a novel method is reported herein, which permits accurate rheological measurements on membrane biofouling layers, using specimens withdrawn from an operating laboratory-scale MBR. A specially designed test-section (with a pair of flat membrane specimens) allows implementation of realistic operating modes, including automatic periodic back-washing. The membrane specimens, with a biofouling layer representative of a well-controlled MBR operating history, are examined in an advanced parallel-plate rheometer, where special care is taken to prevent ex-situ biofouling layer changes. Measurements performed in oscillatory and steady shearing modes provide valuable information on biofouling layer rheological characteristics, confirming that these layers are typical viscoelastic materials with yield stress exhibiting thixotropic, shear-thinning behavior. Rheological properties of the activated sludge liquor are also assessed. The rheological properties of activated sludge and of biofouling layers display qualitative similarities, although the elastic character of the latter is much more pronounced. The new technique is most useful for studying biofouling layers as a function of the main MBR process parameters. Improvements of the technique for such applications are discussed.
    Journal of Membrane Science 01/2015; 482(2015)13–24:13-24. · 4.91 Impact Factor

Full-text

Download
142 Downloads
Available from
Oct 31, 2014