The assessment of coagulation and flocculation performance and interpretation of mechanistic behavior of suspended particles aggregation by alum assisted by tapioca peel starch

The current study describes the synergistic action of a green starch flocculant extracted from agricultural waste coupled with aluminium sulphate to enhance coagulation and flocculation for surface water treatment. The coagulants and the flocs characteristics were analyzed to better understand the physicochemical properties and the underlying mechanisms of the treatment process. Several elements, including Cl and Ca were observed on the surface of the starch, and the presence of essential functional groups such as hydroxyl and carboxyl that help to promote flocculation function was detected. Superior performance was observed in the treatment using alum+TPS compared to the treatment using alum as a sole coagulant. Maximum turbidity and TSS removals of 90.32% and 88.89%, respectively, were attained within 10 minutes of settling time using the recommended alum-TPS dosage of 7.5-50 mg/L at pH 7. The flocs generated by the alum+TPS treatment exhibited distinguishable characteristics with bigger and highly compacted flocs matrix in which colloidal particles enmeshed within the flocs clusters. The combination use of alum+TPS showed the microflocs were initially formed by alum through the charge neutralization mechanism. The later addition of the starch into the suspension revealed that the bridging and sweep flocculation mechanism governs the flocculation process reflected through the shifting of FTIR bands that marked the formation of hydrogen bonding between the starch, alum and the suspended particles. Adding starch into the suspension undoubtedly provided effective entrapment and adsorption by larger-sized polymer, which promotes inter-colloidal particle bridging and subsequently improves the water clarity.