Coagulation mechanism

Description

Mechanism of Particle Removal

Double Layer Compression

The compression of the double layer decreases the energy barrier; thus, the colloids can come closer [27] [28] [29] . This is attained via injecting indifferent electrolytes to the water [30] [31] [32] . The Schultz?Hardy rule shows that the impact of the indifferent electrolytes augments with the valence of the ions by sixth exponential power [33] [34] [35] . As an illustration, one mole of Ca²⁺ possesses the identical impact as 2⁶ ions of Na⁺ on the double layer compression [36] [37] [38] .

Adsorption-charge neutralization

In coagulation method, such a mechanism remains the most cost-efficient pathway [39] [40] [41] . During this route, the positively charged ions and species cover the negatively charged colloids, thereby decreasing the surface charge and by that the energy barrier [42] [43] [44] . This mechanism is cost-efficient tanks to the fact that the neutralization process occurs stoichiometrically between the positively and negatively charged ions [45] [46] [47] . Such a pathway could realize coagulation via inorganic coagulants or cationic organic polymers [48] [49] [50] .

Interparticle bridging

Such route takes place when organic coagulants or organic polymers are employed [51] [52] [53] . Polymers possess threads and fibers that bind the particles into big and compact agglomerates [54] [55] [56] . Polymers with higher molecular weight (MW) are frequently more efficacious, thanks to their long chains [57] [58] [59] .

Colloidal entrapment or “sweep floc”

The final product of the hydrolysis of inorganic coagulants is the hydroxide precipitates that could entrap colloids [60] [61] [62] . Such pathway consumes coagulants in excess of stoichiometry [63] [64] [65] .

Mechanisms of Organic Matter Removal

Natural organic matter (NOM) is the source of natural color in surface waters [66] [67] [68] . NOM removal is fundamental in potable water treatment since it form carcinogenic disinfection by-products (DBPs) [69] [70] [71] . NOM is mostly composed of humic substances (their average size is 0.47 - 3.3 nm) [72] [73] [74] . NOM is quantified by color, ultraviolet (UV) absorption, and total organic carbon [75] [76] [77] . NOM is noted to be retained through all particle removal routes [78] [79] [80] . NOM could dominate coagulant injection and adoption of water treatment technology rather than colloidal particles [81] [82] [83] .