Synthesis, characterization and application of a novel starch-based flocculant with high flocculation and dewatering properties

• An environmentally friendly flocculant was synthesized by grafting DMC onto starch.
• DMC increased cationic properties, molecular weight and thus flocculation ability.
• DMC improved copolymer solubility, and thus made it easy and convenient to use.
• Grafted copolymer exhibited efficient flocculation ability under all pH conditions.
• Grafted copolymer was proven to be superior to PAM for sludge dewatering purpose.

Flocculation process is one of the most widely used techniques for water and wastewater treatment, and also for sludge dewatering. Synthesis of natural biopolymers or modification of natural biopolymers as environmentally friendly flocculants is highly desired in the field of environmental protection. In this work, a water soluble copolymer flocculant, STC-g-PDMC (starch-graft-poly (2-methacryloyloxyethyl) trimethyl ammonium chloride) was synthesized through grafting a monomer, (2-methacryloyloxyethyl) trimethyl ammonium chloride (DMC), onto starch initiated by potassium persulphate. Acetone and ethanol were used for copolymer precipitation and purification in the synthesis, which diminished the toxicity during the synthesis process. The graft copolymer was characterized using Fourier-transform infrared spectroscopy, 1H nuclear magnetic resonance, X-ray powder diffraction, thermogravimetric analysis and elemental analysis. The prepared STC-g-PDMC exhibited a highly effective flocculation capability for kaolin suspensions compared with starch and polyacrylamide as control. The charge neutralization effect played an important role in the flocculation process at low flocculant dosages. When it was used as dewatering agent for anaerobic sludge, the conditioned sludge could be easily filtered after the dosage reached 0.696% of the dry weight of sludge. Such a graft copolymer is a promising green agent for wastewater treatment and sludge dewatering applications.