TY - JOUR
T1 - Sludge fractionation as a method to study and predict fouling in MBR systems
AU - Christensen, Morten Lykkegaard
AU - Niessen, Wolfgang
AU - Sørensen, Natalie Bøie
AU - Hansen, Susan Hove
AU - Jørgensen, Mads Koustrup
AU - Nielsen, Per Halkjær
PY - 2018
Y1 - 2018
N2 - Membrane bioreactors (MBRs) are continuously being improved, but membrane fouling still causes severe problems, so effective measures to reduce fouling are imperative to minimize operational cost. Potential foulants can be found in MBR sludge flocs, but it is not known which fraction(s) that mainly influence fouling and how sludge flocs affect fouling. A standard procedure was developed to separate sludge into floc/colloid, colloid/solute, and solute fractions. The fouling properties of MBR sludge and sludge fractions were evaluated in a lab-scale MBR equipped with aerated flat-sheet membranes. The fastest flux decline took place in the solute fraction due to formation of irreversible fouling; this fraction contained foulants smaller than the membrane pore diameter (0.2 μm), causing pore blocking and/or adsorption. Flux declined more slowly in the colloid/solute fraction, where fouling was more reversible. The external fouling layer on the membrane was shown to protect it from pore blocking/adsorption. Flux decline was slowest in unfractionated MBR activated sludge. Thus, presence of sludge flocs reduced the concentration of foulant and also directly reduced the formation of an external fouling layer by shear. This may be due to surface erosion or more turbulence close to the membrane surface by sludge flocs which thereby partly removed the external fouling layer. To reduce membrane fouling, concentrations of solutes (e.g., macromolecular extracellular substances) and colloids (e.g., single cells) should be kept low and concentration of sludge flocs high.
AB - Membrane bioreactors (MBRs) are continuously being improved, but membrane fouling still causes severe problems, so effective measures to reduce fouling are imperative to minimize operational cost. Potential foulants can be found in MBR sludge flocs, but it is not known which fraction(s) that mainly influence fouling and how sludge flocs affect fouling. A standard procedure was developed to separate sludge into floc/colloid, colloid/solute, and solute fractions. The fouling properties of MBR sludge and sludge fractions were evaluated in a lab-scale MBR equipped with aerated flat-sheet membranes. The fastest flux decline took place in the solute fraction due to formation of irreversible fouling; this fraction contained foulants smaller than the membrane pore diameter (0.2 μm), causing pore blocking and/or adsorption. Flux declined more slowly in the colloid/solute fraction, where fouling was more reversible. The external fouling layer on the membrane was shown to protect it from pore blocking/adsorption. Flux decline was slowest in unfractionated MBR activated sludge. Thus, presence of sludge flocs reduced the concentration of foulant and also directly reduced the formation of an external fouling layer by shear. This may be due to surface erosion or more turbulence close to the membrane surface by sludge flocs which thereby partly removed the external fouling layer. To reduce membrane fouling, concentrations of solutes (e.g., macromolecular extracellular substances) and colloids (e.g., single cells) should be kept low and concentration of sludge flocs high.
KW - Extracellular polymeric substances
KW - Fouling
KW - Membrane bioreactors
KW - Scouring
KW - Specific cake resistance
UR - http://www.scopus.com/inward/record.url?scp=85036458137&partnerID=8YFLogxK
U2 - 10.1016/j.seppur.2017.11.055
DO - 10.1016/j.seppur.2017.11.055
M3 - Journal article
VL - 194
SP - 329
EP - 337
JO - Separation and Purification Technology
JF - Separation and Purification Technology
SN - 1383-5866
ER -