Flocculation of diatomite by a soy protein-based bioflocculant

A novel bioflocculant, methylated soy protein (MeSP), has been developed and its flocculation performance was tested with diatomite suspensions in freshwater (pH 2–11) and in seawater. The flocculation performance of MeSP was much higher than that of commercial polyaluminum chloride (PAC) in terms of supernatant clarity and floc settling velocity. In freshwater and at a fixed flocculant dosage of 60 ppm, MeSP could reduce the relative absorbance to 0.1 within 1 min over a wide pH range (pH 3–10), while PAC was effective only at around pH 5. In seawater (pH 8), there was a striking difference in flocculation performance between MeSP and PAC. MeSP (20–50 ppm) could reduce the relative absorbance to less than 0.1, while PAC was ineffective. The settling velocity of the floc formed by MeSP in freshwater at pH 7 and in seawater was about 4 mm/s. MeSP was applied to the flocculation of a real wastewater generated from an andesite quarry. The relative absorbance could be reduced to less than 0.05 by the addition of 40 ppm of MeSP. The floc settling velocity was about 5 mm/s.