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水体中氮磷营养盐是藻类生长的物质基础,对藻类生长构成上行效应,但过多的营养盐会造成水体的富营养化,引起藻类的增殖暴发甚至形成水华现象。因此,对富营养化水体氮磷营养盐的削减是治理富营养化水体的重要途径。使用镧改性黏土制剂被认为是去除水体磷营养盐的有效手段,近年来在国内外富营养化水体治理工程中得到广泛应用,取得了显著成效[1-3]。镧制剂除磷作用机理为:金属镧可与水体中的可溶性磷酸根结合生成磷镧镨矿沉淀,从而去除水体中的生物活性磷,进而实现对富营养化水体的生态修复[4-5]。在实际的工程应用中,镧改性黏土制剂也存在诸多应用缺陷,镧改性黏土只能与可溶性的磷酸盐反应,难以去除富营养化水体中大量以藻类生物质磷形式存在的颗粒态磷,因此,镧改性黏土用于富营养化水体生态修复通常耗时较长,见效较慢[6]。在藻类暴发的水华时期通常不建议使用该方法。此外,镧改性黏土的使用方式通常是制备成黏土悬液后喷洒于水面,由于黏土自身沉降较为缓慢,因此,常常造成水体浑浊现象并持续一定时间,而黏土颗粒悬浮于水体中对浮游动物、底栖动物、鱼类等水生生物的摄食和呼吸作用造成一定负面影响[7-8]。因此,如何以黏土作为基质材料,对其进行改性使其在具有除磷功能的同时,兼具絮凝除藻降浊的能力是目前亟待解决的问题。
壳聚糖是天然甲壳素部分脱乙酰基后得到高分子化合物,具有良好的生物降解性、生物相容性和无毒性,将壳聚糖溶于酸性溶液,壳聚糖分子具有阳离子型聚电介质的性质,在水生态工程中被成功的用于絮凝除藻,改善富营养化水体的生态环境质量[9-11]。但由于壳聚糖只能溶于pH小于5的酸性溶液中而不溶于中性或高碱性溶液,使得壳聚糖的使用受到较大限制[12]。本研究采用壳聚糖作为黏土改性剂,预先对壳聚糖通过季铵化改性处理,制备出溶于中性水环境的季铵化壳聚糖;再使用季铵化壳聚糖溶液联合镧制剂对膨润土进行复合改性处理,制备出壳聚糖-镧复合改性膨润土;通过絮凝实验验证了其絮凝除藻性能,并通过磷吸附实验分析了其除磷特性,探究了利用复合改性膨润土开展富营养化水体修复实验的效果,以期为富营养化水体的生态修复提供高效的同步除藻固磷的新材料。
壳聚糖-镧改性膨润土的制备及除藻除磷性能
Chitosan-lanthanum modified bentonite preparation and its removal performance of algae and phosphorus
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摘要: 为解决对于富营养化水体同步进行除藻、除磷的问题,采用膨润土作为基质材料,通过壳聚糖和镧进行复合改性处理,制备了壳聚糖-镧复合改性膨润土(CLMB),考察了CLMB的除藻除磷性能及相关的影响因素,并将CLMB用于富营养化水体修复研究。结果表明:制备的CLMB在投加量为50 mg·L−1时,叶绿素a(Chl-a)和浊度去除率分别为95.63%和92.55%;CLMB在pH为4~8及淡水环境下除藻效率较高;CLMB对磷的吸附更适合Langmuir方程和准二级动力学模型,在35 ℃时CLMB对磷的饱和吸附量达到13.46 mg·g−1。CLMB用于富营养化水体修复的结果表明,CLMB具有快速絮凝除藻作用,富营养化水体从修复前的重度富营养化改善至中营养水平,沉水植被得到有效恢复。
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关键词:
- 壳聚糖-镧改性膨润土 /
- 富营养化 /
- 除藻 /
- 除磷
Abstract: In order to achieve simultaneous removal of algae and phosphorus in eutrophic water, bentonite was used as the matrix material, and chitosan-lanthanum composite modified bentonite (CLMB) was prepared through the composite modification of chitosan and lanthanum. Algae and phosphorus removal performance by CLMB, as well as the impact factors, was analyzed. The recovery test of eutrophic waterbody using CLMB was also conducted. The results showed that at the dosage of 50 mg·L−1 CLMB, the removal rates of chlorophyll a and turbidity were 95.63% and 92.55%, respectively. CLMB had higher algae removal efficiencies in fresh water with pH ranging from 4 to 8. The adsorption process of phosphorus on CLMB accorded with the Langmuir isotherm equation and pseudo second-order kinetic equation, and the maximum adsorption capacity was 13.46 mg·g−1 at 35 ℃. The recovery experiment of eutrophic water body showed that CLMB could rapidly flocculate algae and improve water quality. The water quality was improved from severe eutrophication to mesotrophic level. Submerged vegetations were successfully restored after the treatment. -
表 1 CLMB吸附磷的等温参数
Table 1. Isothermal parameters of phosphorus adsorption on CLMB
温度/℃ Langmuir Freundlich qmax/(mg·g−1) KL/(L·mg−1) R2 KF 1/n R2 10 11.47 0.29 0.993 2.58 0.40 0.972 25 11.99 0.27 0.992 2.60 0.41 0.975 35 13.46 0.29 0.992 3.01 0.40 0.975 -
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