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溶解空气气浮(DAF)已经被广泛应用于给水处理、废水处理和中水回用过程[1-2]。虽然DAF对COD、BOD5和TSS有一定程度的去除,但其限制了溶解性有机物的去除[3-4]。由于臭氧具有较强的氧化性,故其作为消毒剂和氧化剂也被广泛的应用于给水和废水处理中[5-6],臭氧氧化的主要目的是脱色和去除天然难降解有机物[7-8]。相比传统的深度处理工艺(混凝+沉淀+过滤),DOF工艺有着较高的脱色、脱臭和有机物去除率[9]。同时,由于DOF工艺将混凝、分离、脱色、除臭和消毒等多个过程集中于同1个操作单元[3],比常规深度处理工艺具有低于4倍的水力停留时间[9],节省了建设费用和土地成本。但臭氧气浮工艺对溶解性有机物的去除效果仍有一定的局限性,未能高效去除二级出水中的残余有机物。
目前,有关气浮工艺的研究大多仍处于基础操作条件的优化[10-11]和气泡大小的改变对气浮工艺去除性能的影响[12-14]。为了进一步提高气浮工艺的去除特性,之前的研究[15-18]着重于溶气水中气泡电荷性质及表面性质的改性对污染物去除特性的影响。ARABLOO等[19]和PASDAR等[20]分别研究了不同浓度表面活性剂和高分子聚合物对气泡理化性质及大小分布的影响。RAO等[21-22]从气泡Zeta电位和PAM剩余浓度等角度对比了聚合物甲基丙烯酸二甲胺基乙酯(N,N-dimethylaminoethyl methacrylate)和N,N-二烯丙基-N,N-二甲基氯化铵(N,N-diallyl-N,N-dimethylammonium chloride)对气泡表面电荷性质改善的效果,并揭示了PAM和微气泡的作用机理。
先前的研究对絮体表面性质的改性,依然停留在不同价态电解质对表面的改性阶段[23-24]。高分子聚合物PAM应用于气浮工艺中大多是改性气泡表面的性质[17-25],很少涉及对絮体表面特性改善的研究。而且,在气浮工艺中微气泡和絮凝体的结合特性通常用去除性能、接触角及絮体形态特征等表征[26-27],尚未从气载絮体的尺寸大小、形态特征等角度阐明气浮效果。本研究探究了阴阳离子型PAM对以腐殖酸为代表的天然有机物在DOF工艺中去除特性的影响,从去除性能、气载絮体大小及分形维数和接触角等多角度阐明污染物和微气泡的结合特性,揭示絮体表面性质对溶解性有机物去除性能的影响。
臭氧气浮工艺絮体尺度与界面理化特性调控
Regulation of the size and interfacial physicochemical properties of flocs in dissolved ozone flotation
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摘要: 针对臭氧气浮工艺对有机物脱色和去除性能的限制,通过阴、阳离子型聚丙烯酰胺(ployacrylamide,PAM)对以腐殖酸为代表的天然有机物絮体的尺度调控,采用气载絮体尺度、二维分形维数及絮体与微气泡间的接触角对PAM浓度梯度下形成的气载絮体进行了表征;研究了阴阳离子型PAM浓度梯度对腐殖酸的降解效果和气载絮体尺度;并探讨了阴阳离子型PAM、絮体与微气泡间的结合机理。结果表明:PAM的投加提高了臭氧气浮工艺中腐殖酸的去除性能,且气载絮体尺寸、分形维数和接触角均有所增大;在不同类型PAM中均存在最佳PAM剂量,在此剂量下,体系内去除效果、气载絮体大小和接触角最大、分形维数最小;在最佳PAM剂量下,与阴离子型PAM相比,阳离子型PAM形成气载絮体的大小和接触角较大,分形维数较小,且去除效果较好。在臭氧气浮体系中,通过改善PAM、絮体与微气泡结合静电作用力的强弱形成了利于气浮的气载絮体尺度,提高了对腐殖酸的去除效果。
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关键词:
- 臭氧气浮工艺(DOF) /
- 腐殖酸 /
- 气载絮体 /
- 形态特征
Abstract: In response to the performance limitations on the decolorization and removal of organic matter by dissolved ozone flotation process(DOF), anionic and cationic polyacrylamide (PAM) were used to regulate floc size of the natural organic matter represented by humic acid, and aerated flocs formed at different PAM concentration gradients were characterized by aerated floc size, two-dimensional fractal dimension and contact angle between flocs and microbubbles. In addition, the effects of anionic and cationic PAM concentration gradients on humic acid degradation and aerated floc size were studied, and binding mechanism among anionic and cationic PAM, flocs and microbubbles was discussed. The results indicated that PAM addition improved humic acid removal in DOF process, and aerated floc size, fractal dimension and contact angle increased. There was an optimal dosage for different kinds of PAM, at which the removal efficiency, aerated flocs size and contact angle were the largest, and fractal dimension was the smallest. Compared with the anionic PAM at its optimum dosage, the formed aerated flocs using cationic PAM were characterized as larger size, higher contact angle, smaller fractal dimension and better humic acid removal effect. In DOF system, favorable aerated floc size could be formed to improve the removal efficiency of humic acid by ameliorate the electrostatic interaction strength among PAM, flocs and microbubbles. -
表 1 臭氧气浮装置的操作条件
Table 1. Standard operational condition for DOF reactor
运行参数 数值 运行参数 数值 原水进水流速/(L·h−1) 120 分离区高度/m 1.5 管道混合时间/s 30 直径/m 0.3 臭氧投加量/(mL·min−1) 60 表面流速/(m·h−1) 2.21 回流水的流速/(L·h−1) 36 水力停留时间/min 40 压力/MPa 0.4 总体积/m3 0.10 -
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