Green Flocculants from Cactus Cladodes: Physicochemical Characterization and Assessment of Their Flocculating Activity for Crystal Violet Dye Removal

Cactus cladodes have been emerged as one of the most popular plant-based flocculants. They have been listed as a promising natural alternative to the noxious synthetic flocculants. However, practical application of this bio-flocculant is still hampered by some questions concerning their formulations’ stability, active agents therein and their flocculating performance. Thus, in this study, three cactus formulations, namely, cactus juice (CJ), cactus lyophilized powder (CLP) and oven-dried powder (CDP) were subjected to a physicochemical characterization to provide an in-depth understanding of the main flocculation active agents and distinguish the suitable preparation method promoting bio-flocculants’ stability and effectiveness. Therefore, their flocculating activity was evaluated in treating a model-colored effluent, a crystal violet (CV) dye solution. The obtained results show that the three cactus formulations exhibit a significant sugars content with considerable calcium amounts. The highest sugars content was registered for CLP thanks to the efficacy of lyophilization method to maintain their stability. Furthermore, the main flocculating active compound was identified as an arabinogalactan composed of long polygalacturonic acid chain backbones with branches of neutral sugar residues involving mostly the arabinose. As for the color removal performance, an outstanding CV removal exceeding 99% was found using CLP under alkaline pH. It was occurred through charge neutralization and bridging mechanisms. Hence, based on these groundbreaking results, the application of cactus formulation-based flocculants, especially the lyophilized one is highly recommended to ensure a clean, eco-friendly and sustainable wastewater treatment approach.

Graphical Abstract