Synthesis and characterization of cassava starch graft poly(acrylic acid) and poly[acrylic acid)-co-acrylamide] and polymer flocculants for wastewater treatment

Starch-g-poly(acrylic acid) and poly[(acrylic acid)-co-acrylamide] synthesized via chemically crosslinking polymerization were then each mixed with inorganic coagulants of aluminum sulfate hydrate [Al-2(SO4)(3)-18H(2)O], calcium hydroxide [Ca(OH)(2)], and ferric sulfate [Fe-2(SO4)(3)] in a proper ratio to form complex polymeric flocculants (CPFs). All CPFs exhibited low water absorbency than those of the uncomplexed superabsorbent copolymers. The color reduction by the CPFs was tested with both synthetic wastewater and selected wastewater samples from textile industries. The synthetic wastewater was prepared from a direct dye in a concentration of 50 mg dm(-3) at pH 7. The CPFs of poly[(acrylic acid)-co-acrylamide] with calcium hydroxide at a ratio of 1:2 is the most effective CPF for the wastewater color reduction. The CPF concentration of 500 mg dm(-3) could reduce the color of the synthetic wastewater containing the direct dye solution by 95.4% and that of the industrial wastewater by 76%. Starch-g-poly(acrylic acid)/Ca(OH)(2) CPF can reduce the synthetic direct dye and the industrial wastewater by 74% and 18%, respectively. Chemical oxygen demand, residual metal ion concentrations, pHs, turbidity of the wastewater were also investigated and the potential use of the complex polymer flocculants for textile wastewater treatment was indicated. (c) 2006 Wiley Periodicals, Inc.