Extracellular polymeric substances (EPS) in a hybrid growth membrane bioreactor (HG-MBR): viscoelastic and adherence characteristics.
Extracellular polymeric substances (EPS) comprising the microbial bioﬁlms in membrane bioreactor (MBR) systems are considered the most significant factor affecting sludge viscoelastic properties as well as membrane fouling. Understanding the water chemistry effects on EPS viscoelastic, conformational, and adherence properties are critical for defining the microbial bioﬁlm's propensity of fouling the membrane surface. In this study, EPS extracted from a hybrid growth membrane bioreactor (HG-MBR) were analyzed for their adherence, viscoelastic properties and size distribution using quartz crystal microbalance with dissipation monitoring (QCM-D) and dynamic light scattering (DLS), respectively. Also, adsorption characteristics of EPS extracted from different locations in the HG-MBR (bioreactor liquor, fluidized carriers, and membrane surface) were defined and linked to the extent of the total polysaccharide content in the EPS. In accordance with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, more EPS were adsorbed at higher ionic strength, lower pH and in the presence of calcium cations. Based on the QCM-D results, the calculated thickness of the EPS adsorbed layer was increased at lower ionic strength, higher pH, and only had a minor increase in the presence of calcium cations. The calculated shear modules and shear viscosity suggest that at lower pH and in the presence of calcium, EPS becomes more viscous and elastic, respectively. DLS analysis correlated to the QCM-D results: A decrease in the hydrodynamic radius of the EPS colloids was observed at lower pH, and in the presence of calcium, most likely attributed to intermolecular attraction forces. Based on this study, low pH and presence of calcium may induce ﬂocs' stability that resist erosion in the MBRs, while on the other hand, these conditions may induce the formation of an elastic and viscous EPS layer fouling the ultrafiltration (UF) membrane.
Zuckerberg Institute for Water Research, Ben Gurion University of the Negev, Sede Boqer Campus, Midreshet Ben Gurion, 84990, Israel.
Wang
W
Ying
Fei
F
Yang
Amos
A
Bick
Gideon
G
Oron
Moshe
M
Herzberg
D000327:Adsorption; D001673:Biodegradation, Environmental; D018441:Biofilms; D057219:Biofouling; D019149:Bioreactors; D002118:Calcium / Q000737:chemistry; D002412:Cations / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D011108:Polymers; D058525:Quartz Crystal Microbalance Techniques; D055682:Viscoelastic Substances / Q000737:chemistry*; D014865:Waste Disposal, Fluid / Q000379:methods
D002412:Cations; D011108:Polymers; D055682:Viscoelastic Substances; D002118:Calcium