Determination of active ingredients of a new coagulant aid-Enteromorpha by floc characteristics on-line monitoring in Yellow River water treatment

• Enteromorpha Po, Pr and Cf was separated and used as coagulant aid respectively.
• Coagulant aid effects were studied by floc on-line monitoring.
• The interaction effect among Cf, Po and Pr was discussed.
• Floc characteristics could be enhanced obviously due to Po and Cf addition.
• Floc produced by AS–Po and AS–Cf possess denser structure.

As a kind of by-product of marine green tides, Enteromorpha can be used as a new coagulant aid in water treatment process for the purpose of “treating waste by waste”. The possible active ingredients (Ai) of this coagulant aid, including polysaccharide (Po), protein (Pr), crud fiber (Cf) and the combination of them (Po–Pr, Po–Cf and Cf–Pr), were extracted and then used as coagulant aid in Yellow River water treatment respectively. The dual-coagulant, aluminum sulfate (AS)-coagulant aid, was achieved by dosing coagulant aid 30 s after AS was dosed. The growth, breakage and regrowth of flocs formed by dual-coagulants were comparatively investigated to determine the Ai of Enteromorpha. The results showed that flocs sizes and growth rates increased by 150–200% due to Po and Cf addition, and meanwhile the strength and recovery ability could be enhanced by 40–50%. Moreover, floc produced by AS–Po and AS–Cf possess larger fractal dimension which means denser floc structure. However, floc characteristics could not be enhanced when Pr was used as coagulant aid. Further discussion indicated that the Ai of Enteromorpha as coagulant aid was Po and Cf, and there was no interaction effect among Cf, Po and Pr.