Aggregation of nano-sized alum–humic primary particles

Abstract

a b s t r a c tIn order to understand the mechanism of floc formation and growth in coagulation process, effect of zeta potential and surface characteristic of nano sized primary particles on coagulation efficiency were investigated by coagulation of humic acid with alum in this study. It was demonstrated that only 1 min rapid mixing was enough for adsorption of humic acid onto the precipitates of alum, and 15 min flocculation (slow mixing) only induced the formation and growth of flocs. The primary particle size of alum-humic flocs was near 50 nm and spherical. Mathematical model deduced from Derjaguin-Landau-VerweyOverbeek (DLVO) theory showed that the formation of micro-flocs (or lag time) was determined by the square value of zeta potential of nano-sized primary particles and intensity of Brownian motion, which is closely related to water temperature. There was an absolute critical zeta potential, i.e. 13.5 mV in this study, determining whether two nano-sized particles could overcome the energy barrier consisted of Van der Waals force and electrical double layer repulsion force to allow floc formation to occur at a certain temperature. The Brownian motion determined whether the nano-sized primary particles (aluminum hydroxide precipitates with humic acid) had the opportunity to overcome the repulsive force and cement with each other. Low coagulation efficiency at high latitude area in winter is caused by low collision frequency, which is mainly attributed to the low intensity of Brownian motion at a low temperature. Furthermore, it was demonstrated that aggregation of micro-flocs or their clusters significantly depended on activated sites on the primary particles rather than the zeta potential of primary particles when sweep flocculation dominated the coagulation mechanism if the size of flocs was larger than some value.Crown

Modelling the structure of sludge aggregates

“…In general, the quality and structure of various types of sludge can be compared quantitatively based on the determined values of fractal dimension D v of aggregates in a given cluster-unit and also on the given cluster-unit size. The variations in the value of D v are determined by at least three principal sludge parameters: (a) sorption capacity [ 1 , 3 ], (b) susceptibility to sedimentation or floating [ 24 ] and (c) susceptibility to dehydration. Sludge aggregates with well-developed and jagged surface structures are therefore characterized by a lower value of D v , and have a greater ability to adsorb pollutants during sweep flocculation [ 1 , 3 ] than aggregates characterized by a more compact structure (higher value of D v and smaller specific surface area).…”

“…Agglomeration and aggregation [ 1 ] are natural phenomena. They are often used in food technology and in the chemical industry to produce, for example, polymers.…”

Efecto de la labranza en la estabilidad estructural y resistencia a la penetración en un Inceptisol sembrado en arracacha (Arracacia xanthorrhiza Bancroft) en Boyacá

“…Después de la preparación del suelo, E2, disminuyeron todos los valores de la DPM, debido a que cambia el orden de los agregados, los cuales son entidades dinámicas y cuya estabilidad depende del tipo de preparación del suelo (García-Orenes et al, 2009), por lo que es probable que esto haya generado las diferencias estadísticas, siendo la LM la única considerada dentro de un rango estable con un valor promedio de 3,177 mm, posiblemente a que no hubo ruptura del suelo (Baumgarten et al, 2012), y que la fuerza de atracción de Van der Walls se mantuvo (Zhang et al, 2012;Yu et al, 2012), y donde las LV y LC presentaron valores promedio de 2,864 y 2,655 mm respectivamente, considerados moderadamente estables (IGAC, 2006). Dexter y Czyz (2011) afirman que los agregados en el rango de 5 a 3 mm son aptos para la emergencia de las plantas, y que la presencia de macroagregados posibilita una fácil accesibilidad a la biomasa microbiana (Awad et al, 2013), parte importante para mantener la estabilidad de agregados a largo plazo (Gentile et al, 2011).…”

Study of Sludge Particles Formed during Coagulation of Synthetic and Municipal Wastewater for Increasing the Sludge Dewatering Efficiency

“…Probably the most important effect of flocs on the structure of municipal wastewater sludge is through aggregation and agglomeration-flocculation (aaf ) processes [26][27][28][29]. Numerous papers have been published, including information about measurements, modeling and characterization of the structure of municipal wastewater sludge [30][31][32][33].…”