改性壳聚糖CAD与微生物絮凝剂MBF8复配絮凝研究

采用水溶液自由基聚合反应,将丙烯酰胺(AM)、二甲基二烯丙基氯化铵(DMDAAC)接枝到壳聚糖分子上制成了阳离子改性壳聚糖(CAD).经FT-IR、XRD、zeta(ξ)电位、凝胶色谱等分析确定,CAD为淡黄色透明液体,pH值为3.7,相对分子质量为2.88×10⁶,阳离子度为16.7,等电点(0.1%溶液)约为pH值10.5,有效成分2.6%,主要特征官能团有羟基、氨基、季铵基和酰胺基, 呈不规则晶体结构.将CAD与相对分子质量3.67×10⁵的多糖类电负性微生物絮凝剂MBF8复配,对浊度12~460 NTU、离子强度3.0 mmol·L^-1的高岭土悬浊液进行烧杯实验.结果表明,MBF8与CAD的最佳使用方式为先投加MBF8后投加CAD,复配比5:3时效果最好,适用的pH范围为6.0~10.0.采用PAC(3.0 mg·L^-1)+MBF8+CAD(1.0 mg·L^-1)复配絮凝,pH=8.0下,对浊度为110 NTU的高岭土悬浊液,浊度去除率>97%,残余铝<0.08 mg·L^-1,絮体大、沉降快,絮凝效果优于PAC+分子量800万、1200万的阴离子PAM及分子量1500万的阳离子PAM.

Flocculation properties of the compound bioflocculant

Cationic modified chitosan (CAD) was made by grafting acrylamide (AM) and dimethyl diallyl ammonium chloride (DMDAAC) to the chitosan molecules through free radical polymerization in aqueous solution. Characterized by FT-IR, XRD and Gel Chromatography, CAD was faint yellow transparent liquid with pH 3.7, relative molecular mass 2.88×10⁶, cationic degree 16.7, isoelectric point (0.1% solution) about pH 10.5 and effective components 2.6%. The main functional groups of CAD were hydroxyl, amino, quaternary ammonium group and amide group. The microbial flocculant MBF8 produced by fermentation of aspergillus fumigatus was polysaccharide electronegativity polymer with relative molecular weight of 3.67×10⁵. The flocculation characteristics of the complex of MBF8 and CAD were investigated by flocculation of pairing kaolin suspension (turbidity 12~460 NTU, ionic strength 3 mmol·L^-1) in beaker. The result showed that MBF8 should be preferentially added with optimum doses ratio 5:3 and pH 6.0~10.0. Under turbidity 110 NTU and pH 8, the combination of PAC (3 mg·L^-1)+MBF8+CAD (1.0 mg·L^-1) showed high efficiency for flocculation of kaolin suspension that could remove up to 97% of turbidity. The residual aluminum was less than 0.08 mg·L^-1. The flocs can be settled quickly due to their compact clustering and the flocculation performance was better than that of PAC + cationic PAM with molecular weight between 8 million and 12 million and of PAC + anionic PAM with molecular weight of 15 million.