| Flocculation is one of the most economical and effective methods of water treatment. The development of new type of flocculants with excellent performance, environmental friendly characteristics is a heated issue in the field of water treatment. A novel flocculant ACATS was prepared through oxidizing, aminating, cationizing and cross-linking with natural polymer corn starch as raw material. The optimal synthesis conditions of oxidized starch, amino starch and ACATS were determined by single factor experiments and orthogonal experiments. The flocculant was characterized by infrared spectroscopy, scanning electron microscopy, thermogravimetry and differential scanning thermal analysis. Flocculating experiments in kaolin suspension, Cr (Ⅵ) aqueous solution and the actual waste water together with dewatering of activated sludge were carried out by ACATS. The major results of this paper are summarized as follows:(Ⅰ) The optimal synthesis condition of oxidized starch:native starch was5g, NaClO was9mL, pH=6, the reaction temperature was30℃, the reaction time was3h. The optimal synthesis condition of amino starch:reaction temperature was40℃, pH=6, molar ratio of ethylenediamine and oxidized starch was4:1, the concentration of ethylene diamine was0.5mol/L, the solvent was70%ethanol, the reaction time was3h. The optimal synthesis condition of ACATS:mass ratio of cationic starch and amino starch was5:2, the amount of crosslinking agent is0.05mL/g, gelatinization time was5min, pH=9, the reaction temperature was40℃, the reaction time was2h. The surface of ACATS is rough; the flocculant ACATS with low pyrolysis temperature and wide pyrolysis range, has lower thermal stability than that of raw material.(Ⅱ) The transmittance of kaolin suspension treated by ACATS to reach maximum97.6%at the dosage of5mg/L. The pH, temperature and ionic strength have significant influence on the flocculation activity of ACATS. The flocculation was more efficient at pH3compared with the others and the absolute value of zeta potential is close to zero. ACATS showed better flocculation properties at lower temperature for kaolin suspension, indicating the flocculation reaction of ACATS was exothermic. Addition of Ca2+and Al3+had negative effect on the flocculation efficiency, flocculation activity decreased with the increase of ionic strength. Removal efficiency of Cr (Ⅵ) increased with increase of ACATS dosage, reach the peak removal rate65.5%at the dosage of7.0g/L(Ⅲ) In the treatment of actual wastewater, the removal of suspended particles (SS) and chemical oxygen demand (COD) reached the peak value at the dosage of66.7mg/L and75.0mg/L, respectively. Flocculation time had little effect on the flocculation of actual wastewater. The flocculation efficiency decreased with the increase of settling time. AC ATS performed better than PAM and Cat St in the treatment of the actual wastewater.(Ⅳ) ACATS had significantly improved dewatering performance of activated sludge. Stirring speed and feed ratio of ACATS had great influence on dewatering performance of activated sludge. When the feed ratio of ACATS was0.15%and stirring speed was30r/min, the performance of sedimentation filtration was optimal. The effect of temperature and mixing mode to dewatering performance of activated sludge was relatively small. Low temperature and mixing mode was clearly more beneficial to improve the properties of the sludge flocs and the performance of sedimentation filtration. The settling performance of the sludge after processing decreased in the order of ACATS> PAC> Cat St> PAM; the filtration performance of the sludge after processing decreased in the order of PAC> ACATS> Cat St> PAM. |
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