Moringa oleifera-derived coagulants for water treatment: Floc structure, residual organics, and performance trade-offs
2022
Murali, Akshay | Hillstead, Kyle D. | Wrobel, Brendan S. | Thomas, D. J. (Daniel J.) | Gonety, Romuald | Tarabara, Volodymyr V.
The study explored the suitability of unfractionated extracts from the seeds of the Moringa oleifera tree as a coagulant for water treatment. The coagulant was obtained by soaking crushed and sieved seeds in a low salinity aqueous solution: a simple and inexpensive alternative to conventional coagulants in settings where specialized expertise and equipment are lacking. The performance of M. oleifera-derived coagulants was quantified in terms of turbidity removal, bacteriophage clearance, concentration of residual organics, as well as meta-parameters such as floc size and fractal dimension. Treating high turbidity clay suspensions at the optimal coagulant dosage (14.7 mg(DOC)/L) and flocculation mixing conditions ([Formula: see text]= 22.4 s⁻¹) removed > 94% of turbidity, similar to that recorded in reference tests with alum. Floc size distribution shifted to larger sizes during the first 10 min of flocculation with no change afterwards, while the floc fractal dimension, [Formula: see text], continued to increase, pointing to the gradual formation of denser ([Formula: see text]= 2.1 to 2.2), more settleable flocs. Preliminary tests with MS2 bacteriophage showed that coagulation with M. oleifera decreased the viable MS2 titre by ~ 1.3 log, which was significantly above the turbidity removal (~ 1 log). The extraction process, however, allowed a large amount of residual organics (> 78% of extracted DOC) into the treated water. Combining the coagulants with downstream filtration and adsorption, employing UV or solar disinfection, or limiting applications to non-potable reuse is suggested for mitigating the concerns related to residual DOC.
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