Effect of grewia spp. biopolymer on floc properties of coagulated laterite suspension

Abstract

Effect of Grewia spp. biopolymer on the morphological characteristics and strength of laterite flocs coagulated using two common inorganic coagulants was studied. Physicochemical properties of the biopolymer obtained from Grewia spp. barks were determined using elemental analysis, gel perme-ation chromatography, zeta potential measurement, IR and NMR spectroscopy, etc. Zeta potential (–24.64 ± 0.49 mV) measured in aqueous medium at pH 7 revealed that the polymer is anionic in nature. Polysaccharides were identified as the major constituent of the polymer responsible for its flocculation property. Aqueous laterite suspension was subjected to jar test at different pH using iron [Fe2 (SO4 )3 ] or alum [Al2 (SO4 )3 ] as coagulant either alone or in combination with Grewia spp. biopoly-mer. The fractal characteristics of the flocs under different experimental conditions were investigated using a non-invasive image analysis tool. Floc properties were found to be dependent on the pH of the aqueous suspension. Compact flocs were formed in lower pH. An increase in pH resulted in a looser floc structure. Grewia spp. biopolymer in combination with iron or alum resulted in more compact floc formation. Fractal dimensions of only iron-coagulated flocs having floc strength 51.22%–59.94% increased from (1.27 ± 0.09, 1.29 ± 0.06 and 1.23 ± 0.04) to (1.84 ± 0.12, 1.75 ± 0.14 and 1.62 ± 0.09) at pH 5, 7 and 9, respectively with floc strength as high as 81.58%–94.99%. Only alum-coagulated flocs having floc strength ranging between 54.81% and 56.38% and fractal dimensions 1.24 ± 0.06, 1.28 ± 0.07 and 1.23 ± 0.07 at pH 5, 7 and 9, respectively became more compact in presence of the biopolymer (floc strength 87.30%–91.80% and fractal dimensions 1.75 ± 0.07, 1.64 ± 0.08, 1.62 ± 0.11 at pH 5, 7 and 9, respectively). The present study demonstrates that Grewia spp. biopolymer has the potential to be used as an effective coagulant aid over a wide pH range.