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湖泊、水库等水体富营养化是目前全世界共同面临的重大环境问题之一[1-3]。当湖泊、水库等水体中的藻细胞浓度达到每升水中100万细胞以上时,此类水可被称为高藻水,其叶绿素含量可达到100 μg·L−1以上[4]。在太湖和许多富营养化湖泊,夏秋季高藻水导致的蓝藻水华漂浮在水面,堆积在岸边,并在高温下分解,形成恶臭,对水体环境和周边居民生活带来严重威胁[5-6]。
打捞法、直接过滤除藻和清淤法常用于处理藻含量较低的水体[7]。李贵霞等[8]采用均质石英砂作除藻滤料,藻类平均去除率达到90%以上,且出水浊度降低至5 NTU。但直接打捞清淤和过滤除藻的效率较低,并且过高的藻含量带来高昂的处理成本。气浮法通过生成的微小气泡带动藻絮体上浮完成固液分离,能够有效去除水体中藻类[7]。胡澄澄等[9]利用沉淀和气浮工艺处理含藻太湖水,去除率达到85%~95%,但藻源有机物的干扰导致的无效气浮会使得去除效率下降[10]。混凝沉淀法则利用絮凝剂使水体中藻类聚集形成絮状体并絮凝沉淀,该技术成熟使用方便,但易在水体中残留金属离子造成二次污染[11]。氧化除藻是蓝藻水华爆发期间常用的藻类控制方法。KNAPPE等[12]利用高锰酸钾氧化灭活藻细胞,藻的去除率随着高锰酸钾氧化时间和投量的增加而增加。高锰酸钾氧化后也可原位生成具有强吸附性能的二氧化锰,起到助凝作用。臭氧氧化作为目前应用最广泛的强化给水处理工艺之一,很多学者报道臭氧氧化可以改变藻细胞的形态结构、稳定性以及有机物的结构[13-14]。SUKENIK等[15]对比了氯、ClO2、臭氧对藻类混凝的影响。结果表明,臭氧可以改变藻类分泌物的性质,使藻类细胞外分泌物的分子质量变小。ROSITANO等[16]的研究表明,当藻毒素质量浓度为20 μg·L−1时,臭氧氧化5 min后,藻毒素去除率可达100%。另一方面,尽管氧化工艺取得的灭藻效果较好,氧化过程可使藻细胞破裂,溶出藻细胞的胞内含物,但大量藻源有机质(algal organic matter, AOM)的存在也使得水体溶解性有机碳(dissolved organic carbon, DOC)含量升高。同时,氧化过程也造成硝酸盐、磷酸盐等无机盐浓度大幅升高[17-19]。吸附法是最常用的去除这些污染物的手段,强碱阴离子交换树脂凭借其季胺基团可以高效与电负性污染物发生离子交换作用而对其进行去除,因此,有望通过阴离子交换树脂对臭氧氧化后的含藻水进行深度净化。
综上所述,开发基于臭氧氧化和树脂吸附的高藻水应急除藻工艺具有重要意义。因此,本研究对不同藻含量的水样进行臭氧氧化处理,对水样中DOC、叶绿素a(chlorophyll a, Chl-a)、
${\rm{NH}}_4^{+} $ -N、${\rm{NO}}_3^{-} $ -N、总氮(total nitrogen, TN)、总磷(total phosphorus, TP)、微囊藻毒素(microcystin-LR, MC-LR)等水质参数进行了检测。此外,利用商业化的磁性树脂MIEX和硝酸盐选择树脂A520对模拟氧化出水进行深度吸附处理,探究了此过程中藻内含物转化及树脂吸附净化机制。
含藻水臭氧化过程中藻内含物转化及树脂吸附净化
Transformation of algae inclusions during ozonation of algae-laden water and the advanced treatment of ozonized effluent by resin adsorption
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摘要: 随着我国许多湖泊、水库等水体富营养化加重且暴发季节性蓝藻水华,饮用水安全受到极大威胁。为实现含藻水的深度净化,本研究对不同藻含量水样进行臭氧化处理,考察了氧化过程中藻内含物的释放和转化规律,对溶解性有机碳(DOC)、叶绿素a(Chl-a)、
${{\rm{NH}}_4^{+} }$ -N、${{\rm{NO}}_3^{-}} $ -N、总氮(TN)、总磷(TP)及微囊藻毒素(MC-LR)等水质参数的动态变化进行了分析。针对氧化出水DOC和${{\rm{NO}}_3^{-}} $ -N含量高的特征,选取商业化的A520和磁性MIEX树脂进行了深度吸附处理。结果表明:随臭氧化时间的延长,颗粒态藻细胞内含物逐渐变为溶解态并被氧化降解。对于高藻含量水样,氧化过程中${{\rm{NH}}_4^{+}} $ -N迅速积累,有机氮主要转化为${{\rm{NH}}_4^{+}} $ -N;而对于低藻含量水样,有机氮及${{\rm{NH}}_4^{+}} $ -N迅速转化为${{\rm{NO}}_3^{-}} $ -N,最终${{\rm{NH}}_4^{+}} $ -N对TN的占比低于10%。臭氧化过程中,MC-LR质量浓度表现出先升高后降低的趋势,未被氧化降解的MC-LR可被2种阴离子交换树脂有效吸附去除,同时树脂吸附处理可显著降低水体的DOC和${{\rm{NO}}_3^{-} }$ -N含量。因此,臭氧氧化耦合阴离子交换树脂吸附可实现含藻水样的深度净化,为含藻水应急处理提供了新思路。Abstract: Many lakes, reservoirs and other water bodies in China are seriously eutrophicated with the occurenc of seasonal cyanobacteria blooms, which seriously threatens the safety of drinking water. In this study, water samples with different algal contents were treated by ozonation, and the release and transformation of algal inclusions during the oxidation process were investigated. The dynamic changes of water quality parameters such as dissolved organic carbon (DOC), chlorophyll a (Chl-a),${\rm{NH}}_4^{+} $ -N,${\rm{NO}}_3^{-} $ -N, total nitrogen (TN), total phosphorus (TP) and microcystin-LR (MC-LR) were analyzed. According to the characteristics of high DOC and${\rm{NO}}_3^{-} $ -N contents in the oxidized effluent, commercial A520 and magnetic MIEX resin were selected for advanced adsorption treatment. The results showed that with the prolongation of ozonation time, the cell inclusions in granular algae were gradually dissolved and degraded by oxidation. For water samples with high algal content,${\rm{NH}}_4^{+} $ -N accumulated rapidly during the oxidation process, and the organic nitrogen mainly converted to${\rm{NH}}_4^{+} $ -N. However, for water samples with low algal content, organic nitrogen and${\rm{NH}}_4^{+} $ -N rapidly converted to${\rm{NO}}_3^{-} $ -N, and the final ratio of${\rm{NH}}_4^{+} $ -N to TN was less than 10%. The concentration of MC-LR increased first and then decreased during the ozonation processes, and the the undegraded could be effectively removed by two kinds of anion-exchange resins. Meanwhile, the contents of DOC and${\rm{NO}}_3^{-} $ -N in water can be significantly reduced by resin adsorption treatment. Therefore, ozonation coupled with anion exchange resin adsorption can realize the deep purification of algae-laden water, providing a new idea for emergency treatment of algae-laden water. -
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