Insight on an Eco-Friendly Flocculation Using Cactus Extracts: Synthetic Dye and Heavy Metals Removal

Abstract

Over these last years, there is no doubt that the conventional chemical flocculants commonly used for wastewater treatment have been a source of serious human health threats and environmental damage. Consequently, safe and eco-friendly substitutes are worth looking for and assessing. Within this line, flocculants derived from cactus namely, cladodes juice (CJ), powders of lyophilized (CLP) and oven-dried (CDP) cladodes, were developed as alternatives to the noxious synthetic ones. The flocculating activity of these three extracts was evaluated in treating a synthetic Disperse Blue-1 (DB-1) dye solution and a real industrial effluent loaded with heavy metals. A prominent DB-1 removal of up to 80% was achieved using CJ, CLP and CDP. Significant colour and turbidity reductions (94%) were attained using only 20 mg/L of CLP. Likewise, the cactus bio-flocculants complementing alum as a coagulant ensured an enhanced Zn removal from the industrial wastewater. For instance, both CLP and CDP allowed salient Zn uptake exceeding 99% against 69% using the CJ formula. The slight disparity in the flocculating activity between these three formulations could be ascribed to their preparation procedures affecting the integrity of their active agents (polysaccharides and chiefly polygalacturonic acid). Further, it is thought that the presence of hydroxyl (–OH) and carboxyl (–COOH) groups on this latter’s backbone confers the cactus extracts a notable flocculating ability regardless of the type of water pollutants. The plausible flocculation mechanisms for DB-1 molecules and Zn removal are assumed to be adsorption-bridging and adsorption-charge neutralization, respectively.