Design of amphoteric chitosan flocculants for phosphate and turbidity removal in wastewater

An amphoteric flocculant (CMC-CTA) was synthesized by grafting 3-chloro-2-hydroxypropyl trimethylammonium chloride onto carboxymethyl chitosan (CMC). The turbidity and orthophosphate (P_i) removal properties of chitosan (CHI), CMC, and CMC-CTA were compared in the presence (and absence) of FeCl₃ coagulant. At a fixed FeCl₃ dosage, the effects of flocculant dosage, pH and settling time were evaluated. Turbidity removal (%) and optimal dosage (FeCl₃; mg/L) was determined: CMC-CTA (95.8%;5), CHI (88.8%;7.0) and CMC (68.8%;9.0). The corresponding P_i removal (%) and dosage (mg/L) are listed: (93.4%;10), (90.6%;10), and (67.4%;5). Optimal turbidity and P_i removal occurred at pH 4, where CMC-CTA had greater efficiency over CMC and CHI. The turbidity removal kinetics was described by the pseudo-second-order model, while P_i removal followed the pseudo-first-order model. The removal process involves cooperative Coulombic interactions between the biopolymer/Fe(III)/P_i and/or kaolinite colloids, along with polymer bridging effects.