Investigation of Self-Assembly Processes for Chitosan-Based Coagulant-Flocculant Systems: A Mini-Review

Abstract

The presence of contaminants in wastewater poses significant challenges to water treatment processes and environmental remediation. The use of coagulation-flocculation represents a facile and efficient way of removing charged particles from water. The formation of stable colloidal flocs is necessary for floc aggregation and, hence, their subsequent removal. Aggregation occurs when these flocs form extended networks through the self-assembly of polyelectrolytes, such as the amine-based polysaccharide (chitosan), which form polymer “bridges” in a floc network. The aim of this overview is to evaluate how the self-assembly process of chitosan and its derivatives is influenced by factors related to the morphology of chitosan (flocculant) and the role of the solution conditions in the flocculation properties of chitosan and its modified forms. Chitosan has been used alone or in conjunction with a salt, such as aluminum sulphate, as an aid for the removal of various waterborne contaminants. Modified chitosan relates to grafted anionic or cationic groups onto the C-6 hydroxyl group or the amine group at C-2 on the glucosamine monomer of chitosan. By varying the parameters, such as molecular weight and the degree of deacetylation of chitosan, pH, reaction and settling time, dosage and temperature, self-assembly can be further investigated. This mini-review places an emphasis on the molecular-level details of the flocculation and the self-assembly processes for the marine-based biopolymer, chitosan.

Effectiveness of biopolymer coagulants in agricultural wastewater treatment at two contrasting levels of pollution

“…The highest reductions were achieved at dose of 10 mL/L, however dose of 3 mL/L gave almost equal results. The phosphorus and turbidity reductions were at the higher end of spectrum compared to results in previous studies with biopolymer coagulants [25,31,32]. Moreover, the turbidity reductions were very high compared to previous experiments done with polluted river surface water, where around 65% reductions in turbidity were achieved with tannin [28].…”

“…The pH in Ruukki drainage ditch and Tarvaala wetland water samples was near-neutral (6.9 and 6.6, in drainage ditch and wetland, respectively). The performances of several biopolymer coagulants have been observed to be inert to variation in pH [22,30] or have their best performance in slightly acidic [24,25,31] or in neutral conditions [14,19,20,24,32].…”

“…Several studies have tested the coagulation and flocculation properties of biopolymers to organic [14][15][16][17][18] and inorganic [19][20][21][22][23][24] contaminants and at different levels of pollution, pH and dosage. Especially, the coagulation and flocculation properties of chitosan are rather extensively studied [13][14][15][16][17][18][19][20][21][22][23][24][25][26]. However, the vast majority of these experimental studies have simultaneously tested only one biopolymer and used synthetic and homogenous wastewater in the experiments [17,[19][20][21][22]27].…”

Chitosan for direct bioflocculation of wastewater

“…The performance of amphoteric chitosan flocculants can be tuned for optimal performance at variable pH conditions in response to the type of waterborne contaminant species. Thus, the overviews provided herein and elsewhere (Wilson 2014;Bhalkaran and Wilson 2016) reveal the utility of such biopolymeric flocculants for wider applications aimed at oxoanion removal in water and wastewater treatment.…”

“…Crini thus spoke of two-in-one materials (Crini and Badot 2007;Crini et al 2009a, b). Several recent reviews have demonstrated that direct bioflocculation is an effective and competitive approach, and that chitosan is a promising bioflocculant for environmental and purification purposes (Chong 2012;Lee et al 2014;Crini 2015;Bhalkaran and Wilson 2016;Laamanen et al 2016;Yang et al 2016;Kanmani et al 2017;Ummalyma et al 2017;Wang and Zhuang 2017;Desbrières and Guibal 2018;Pakdel and Peighambardoust 2018;Song et al 2018;Salehizadeh et al 2018, Van Tran et al 2018Crini et al 2019;Vidal and Moares 2019).…”