Alternatives to the use of synthetic organic coagulant aids in drinking water treatment: improvements in the application of the crude extract of Moringa oleifera seed

Abstract

[EN] Drinking water treatment is a process based on multiple stages that has a main objective to provide water safe enough to be consumed by humans. Coagulation–flocculation is used to remove colloidal and suspended solids. This process improves the performance of subsequent stages (as sedimentation or filtration) as well as the water quality with a desired end-use. For many years, inorganic and organic synthetic polyelectrolytes have been used in coagulation–flocculation processes. However, its use has been deeply studied recently to determine the potential impact of residual concentration of these substances on human health and the environment. Strict regulations limit the concentration of free residual monomer after the addition of polyacrylamide (PAM) in drinking water treatment and study the effect of interaction of the residues with disinfection products. Therefore, in the last years there has been a resurgence of interest to use natural materials with the same performance that synthetic, but with lower hazard for the environment and humans. This work studies the use of the flocculant extracted from Moringa oleifera seed, in combination with polyaluminum chloride (PAC). The performance is compared with the combination PAC–PAM in terms of coagulant activity and physical–chemical quality of the water treated. Jar test was carried out using two types of natural water (with presence of bentonites) and different combinations of coagulant and flocculants. Results show that coagulant activity of PAC–Moringa combination is comparable with the results obtained with PAC–PAM, reducing initial turbidity up to 90% in all the tests. With regard to physical–chemical quality of the treated water, PAC–Moringa produces values under the drinking water quality standards for all the parameters analyzed. It is remarkable that the decrease of 50% in the trihalomethanes formation potential rate shown for PAC–Moringa combination, observed when treating natural water with presence of bentonites. Therefore, the results obtain in this work encourage the use of Moringa oleifera extract as a natural, low cost, effective, and low-toxicity alternative to the use of synthetic organic polyelectrolytes as polyacrylamide for drinking water treatment.