|Abstract||Membrane bioreactor (MBR) is a recent biological treatment process in many
industrial and municipal industries that has been implemented to overcome the current
difficulties of activated sludge (AS) processes for separation of biomass from the
treated water and the sludge volume reduction. Improvement of MBR sludge
dewaterability is greatly hindered by the presence of large amounts of interstitial
wastewater molecules trapped in the sludge as a result of strong hydrophilic
characteristics and high organic content.
Since, about 40-50% of the wastewater operating cost belongs to the sludge
dewatering stage (i.e., filtration and centrifugation), sludge conditioning is required to
effectively separate solid-liquid and enhance the efficiency of dewatering stage which
has a real impact on the subsequent unit operations such as storage, pumping,
transportation, and handling.
Organic polyelectrolytes such as polyacrylamide (PAM) are generally preferred
for sludge conditioning and they are considered as the most efficient flocculating agents
among the most important breakthroughs in solid-liquid separations. The flocs formed
through charge neutralization and bridging mechanisms using organic polyelectrolyte are sufficiently large and strong and can be separated by physical means like
sedimentation, and they are highly resistant to any breakage due to the hydrolysis stress.
Therefore, this study aims to investigate the influence of polyelectrolyte-based
flocculants (i.e., PAMs) with different molecular architecture (linear, slightly and
highly branched), charge density (CD) and molecular weight (MW) on the electro
kinetics, dewatering, and rheological characteristics of highly stable industrial MBR
sludge. The impact of PAM on flocculation is manifested in the supernatant turbidity,
particle zeta potential, sludge capillary suction time (CST), floc size and settleability.
Turbidity removal and reduction in zeta potential (ζ) are used to identify the optimum
polymer dose. Overall, this work has been successful in establishing the relationship
between electro-kinetic and rheological properties of MBR sludge and correlating these
properties to the MBR sludge dewaterability and volume reduction.