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城市湖泊是城市生态系统的重要组成部分,对人们的娱乐生活、休闲活动等具有重要的作用。然而,随着经济的高速发展,造成大量污染物进入城市河道以及湖泊,造成城市河湖普遍出现富营养化问题,蓝藻水华暴发,破坏湖泊生态系统稳定,引起城市景观水体环境恶化[1-3]。有研究[4-6]表明,水浊度是与湖泊生态系统健康和提供生态系统服务有关的较重要的水质参数之一。作为城市的重要景观水体,城市河湖存在着大量悬浮的胶体颗粒,水体浊度较高,使得水体透明度降低,不仅影响城市湖泊生态系统的结构和功能[7-8],而且还影响人类的水供应,降低城市湖泊的娱乐价值。目前,针对城市河湖水体高浊/藻问题的解决办法主要有物理冲稀、絮凝沉降等。其中,絮凝已被归类为快速去除藻类和浊度的最具成本效益和最简单方便的方法[9-11],而在絮凝过程中,絮凝剂是至关重要的[12-13]。
自1990年以来,天然黏土絮凝有害藻华的能力已得到认可,并开始作为一种低成本和环保的材料应用于工程项目中[14-15]。黏土絮凝是基于水悬浮液中黏土颗粒的物理和化学性质。由于带有不同的表面电荷,黏土颗粒与其他黏土或非黏土颗粒形成聚集体或絮凝物,从而增加其重量,使这些含有藻类细胞的絮凝物沉入底部[16]。之后藻类细胞分解释放的营养物质可以被淹没的植被利用,并促进从以有害藻华为主的水域向以植被为主的水域的转变[17-18]。与成本相对较高且对环境影响较大的化学和生物方法相比,黏土絮凝被认为是最有前途和最实用的控制/缓解技术[19]。然而,天然黏土在去除藻类细胞方面效率低下,在仅使用天然黏土进行絮凝条件下需要高剂量(0.25~2.5g·L−1),以实现相对较高的(>90%)去除效率[20-22],但黏土的高负荷使用可能会引起生态问题[23]。因此,为减少黏土的使用,提高有害藻华的去除效率,需要开发不同的改性剂来增加其比表面积、孔径和表面活性位点等方式,提高其吸附性能[24-25]。
凹凸棒土(attapulgite,AT)是一种具有层链状结构和纳米棒状晶体形态的天然含水富镁铝硅酸盐黏土矿物[26],具有较大的比表面积、丰富的纳米孔道和活性表面基团等特点,因而表现出优异的吸附性、催化性、离子交换性和化学惰性等诸多特性[27]。由于其独特的层状结构和孔隙,经常被用作环境污染控制和修复的吸附剂[28]。张红兵等[29]将壳聚糖改性凹凸棒土作为小球藻的絮凝剂,研究得出在最佳絮凝条件下,对小球藻的絮凝率可达88.7%。JIN等[30]制备了一系列由不同原料配比的阳离子淀粉-凹凸棒土复合混凝剂分别凝固初始浊度为80 NTU的高岭土悬浮液和叶绿素a为0.25 mg·L−1的小球藻悬浮液,其最大浊度和叶绿素a去除率分别为92.2%和100%。董锐等[31]选择三元接枝改性壳聚糖与凹凸棒土进行复配,在最佳絮凝条件下对小球藻去除率可达98.8%。周庆等[32]研究采用凹凸棒土与聚合氯化铝(polyaluminum chloride,PAC)复合改性来去除藻类,结果表明,改性后絮凝材料对蓝藻的去除率显著高于原料本身和原料直接复配,去除率可达97.15%左右。越来越多研究表明,有机和无机改性剂的联合使用能够增强黏土对有害藻华的去除能力[33-35]。聚丙烯酰胺(polyacrylamide,PAM)是一种环境友好型的有机高分子絮凝剂,由于支链上的酰胺基对悬浮颗粒物具有较强的吸附能力、价格便宜等特点,在水处理中得到广泛应用。张雅琪等[34]使用PAC-PAM复合改性粘土去除抑食金球藻,取得了较好去除效果。
针对城市河湖高浊度以及高藻等环境问题,本研究拟利用凹凸棒土为改性材料,通过与聚合氯化铝以及聚丙烯酰胺进行复配组合,研发出一种可用于城市河湖水体浊度以及藻类去除的复合絮凝材料。同时,将该复合絮凝材料用于高藻水体除浊除藻实验,探讨单因素对新型复合絮凝材料去除浊度以及藻类的影响,以优化最佳应用条件。最后,拟通过研究电子显微镜下观察到的藻细胞形态以及投加不同复合絮凝材料所形成的絮体形貌差异,结合改性材料前后的理化性质,探究该复合絮凝材料的除浊除藻机理。
聚合氯化铝/聚丙烯酰胺复合改性凹凸棒土絮凝材料的制备及其除浊除藻效果
Preparation of polyaluminium chloride/polyacrylamide composite-modified attapulgite flocculation material and its removal effect of turbidity and algae
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摘要: 蓝藻水华已成为我国湖库面临的主要环境问题,而利用黏土治理有害藻华技术在我国应用已有十多年的历史,是国际上公认的最具发展前景的措施之一。通过选用凹凸棒土(AT)为原材料,聚合氯化铝(PAC)、聚丙烯酰胺(PAM)作为改性剂,制备新型复合絮凝材料凹凸棒土-聚合氯化铝-聚丙烯酰胺(AT-PAC-PAM)。比较不同原料配比条件下复合絮凝材料的除浊效果,并对絮凝材料改性前后微观形貌、物化性质进行表征分析,然后通过单因素实验对复合絮凝材料除浊除藻条件进行优化,最后采用电子显微镜观察不同絮凝材料处理藻液所生成的絮体形貌差异。研究结果表明:AT-PAC-PAM絮凝材料的最佳原料组分质量配比为m(AT)∶m(PAC)∶m(PAM)=100∶20∶0.2;材料改性后铝离子含量增加、表面积增加、孔径增大、空隙增多,使得吸附能力增强;在相同实验条件下,AT-PAC-PAM(20%)除浊除藻效果最优,其最佳条件为pH =7、复合絮凝材料质量浓度为60 mg·L−1、藻液初始浊度50 NTU、慢搅转速100 r·min−1、慢搅时间20 min、沉淀时间30 min;在对絮体微观观察中发现,复合絮凝材料AT-PAC-PAM加强了吸附架桥和网捕作用,使所形成的絮体密集紧实,从而促进藻-土复合絮体的沉降,具有很好的应用前景。Abstract: Cyanobacterial blooms have become the main environmental problems faced by lakes and reservoirs in our country, and the technology of using clay to control harmful algal blooms has been used for more than ten years, which is internationally recognized as one of the most promising measures. A new composite flocculation material, attapulgite-polyaluminum chloride -polyacrylamide (AT-PAC-PAM), was prepared by selecting attapulgite (AT) as the raw material and polyaluminum chloride (PAC) and polyacrylamide (PAM) as modifiers. The turbidity removal effects of the composite flocculation materials with different raw material ratios were compared, the microscopic morphology and physical and chemical properties of the flocculating materials were also characterized before and after modification. Then, the turbidity and algae removal conditions of the composite flocculation materials were optimized through single-factor experiments, and finally, electron microscopy was used to observe the differences in the morphology of the flocs produced by different flocculating materials treating algal solutions. The results showed that the optimum ratio of m(AT):m(PAC):m(PAM) was 100:20:0.2 for the AT-PAC-PAM flocculation materials; the modification of the materials increased the aluminium ion content, the surface area, the void space and the pore size, which enhanced the adsorption capacity. Under the same experimental conditions, AT-PAC-PAM (20%) had the most remove effects of turbidity and algae. The optimal conditions were following: pH7, composite flocculating material mass concentration of 60 mg·L−1, and the initial turbidity of the algae liquid of 50 NTU, slow stirring speed of 100 r·min−1, 20 min slow stirring and 30 min settling. It was found that the composite flocculation material AT-PAC-PAM enhanced the adsorption bridging and net trapping effects, resulting in the formation of dense and compact flocs, thus promoting the settlement of algae-soil composite flocs, which has good application prospects.
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表 1 凹凸棒土及复合絮凝材料的理化性质
Table 1. Physical and chemical properties of attapulgite and composite flocculation materials
絮凝材料 La/
(mg·g−1)Al/
(mg·g−1)Ca/
(mg·g−1)Fe/
(mg·g−1)K/
(mg·g−1)Mg/
(mg·g−1)P/
(mg·g−1)Cu/
(mg·g−1)Na/
(mg·g−1)BET/
(m2·g−1)孔径/
nmAT 0.03 47.91 40.32 33.92 8.20 56.24 0.80 0.02 2.15 61.72 3.41 AT-PAC(20%) 0.10 79.91 26.28 20.92 4.38 38.15 0.40 0.03 2.20 73.38 33.90 AT-PAC-PAM(20%) 0.45 71.62 26.09 23.28 4.85 37.94 0.42 0.04 4.41 92.20 37.80 -
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