Influence of Polyelectrolyte’s Architecture On the Electro Kinetics and Rheological Behavior of Industrial Membrane Bioreactor Activated Sludge

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.