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由于氮、磷等营养元素大量释放,天然水体中藻细胞疯长进而引发水华现象[1- 2],藻水华爆发不仅严重破坏生态系统[3],也会干扰饮用水水厂正常运行[4-5],安全有效地去除水体中的藻类已成为当下国内外学者研究的热点问题[6]。
藻类在生长代谢过程中分泌的有机物会导致饮用水水质发生恶化,增加了水厂在常规水处理过程中的负担[7- 8]。饮用水处理厂内常见的去除藻类的方法有混凝法、预氧化法、气浮法等[9, 10]。其中,预氯化是应用最为广泛的高藻水处理办法,预氯化是指在投加混凝剂之前或同时加入定量的氯,该方法可以使藻细胞失活同时改变藻细胞的表面形态[11-12]。预氯化通过破坏藻细胞与其表面有机物之间键合方式使其与有机物脱附,并以此改变藻细胞的电负性以及空间位阻效应进而使藻细胞脱稳,从而实现提高混凝除藻效果的目的[12]。
在高藻水的预处理过程中,藻细胞表面停留性有机物(surface-adsorbed organic matter,S-AOM)不仅限制了传统的“混凝-沉淀工艺”对藻细胞及其代谢物的去除效果,还有可能对后续的水处理工艺产生不利影响,进而降低饮用水处理厂的处理效率[13- 14]。预氯化作为强化混凝除藻的前处理工艺已广泛应用于高藻水的预处理中[15- 16],有研究[17]证实了氯会优先与S-AOM反应。S-AOM可提高藻细胞在水体中的稳定性使其难以被混凝去除,故在高藻水的预处理过程中脱附S-AOM 成为提高混凝除藻效果的有效方法之一[18]。此外,预氯化可能造成藻细胞胞内有机物(intracellular organic matter, IOM)的释放,进而增加后续消毒工艺中氯化消毒副产物的生成风险,故预氯化混凝除藻技术的关键在于藻细胞脱附 S-AOM 的同时不损伤藻细胞。
综上所述,本研究首先研究了S-AOM 对藻细胞在水体中的稳定性及混凝去除效果的影响,分别考察S-AOM 脱附程度对混凝除藻效果的影响,进而通过预氯化对藻细胞S-AOM 进行调控,考察了藻细胞S-AOM 在不同氯投量下的脱附情况对藻细胞表面特性及混凝除藻效果的影响,以建立一种在不破坏藻细胞完整性的前提下,达到预氯化强化混凝除藻效果。此外,由于氯的存在会引起藻细胞的程序性死亡(programmed cell death, PCD)[9, 19],为此,还研究了预氯化后的输水过程对混凝除藻效果的影响,以期对需要长距离输送到饮用水厂的高藻源水的预氯化过程提供参考。
预氯化输水对表面停留性有机物及混凝除藻的影响
Effect of pre-chlorination on surface-adsorbed organic matter and coagulation for algae removal in water transportation
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摘要: 针对预氯化这一常用的预氧化方法,考察了表面停留性有机物(S-AOM)在这一过程中对铜绿微囊藻起到的关键作用。同时,探讨了表面停留性有机物及藻的氧化应激对混凝除藻效果的影响。结果表明,预氯化过程可实现适度预氯化的最佳氯投加量,适度预氯化可以在实现脱附S-AOM的同时不损伤藻细胞,强化后续混凝除藻的效果。此外,经过适度预氯化后的藻细胞在远程输水过程中可能会发生程序性死亡,胞内有机物不断泄漏,这仍会对水厂混凝除藻效果产生不利影响。因此,预氧化后藻细胞发生程序性死亡是预氯化强化混凝工艺需要考虑的关键因素。Abstract: Aiming at the pre-chlorination, a commonly used pre-oxidation method, the pivotal role played by surface-adsorbed organic matter (S-AOM) in this process on Microcystis aeruginosa was studied, the influence of S-AOM and algal oxidative stress on coagulation for Microcystis aeruginosa removal was also investigated. The results showed that pre-chlorination could determine the optimal chlorine dosage for achieving moderate pre-chlorination. Moderate pre-chlorination effectively promoted the desorption of S-AOM without causing harm to algal cells, thereby enhanced the subsequent coagulation-based algal removal. In addition, that algal cells subjected to moderate pre-chlorination might undergo programmed cell death during long-distance water transmission, and the continual leakage of intracellular organic matter occurred, which could still adversely affect the efficiency of algal removal during water treatment. Therefore, the programmed cell death of algal cells caused by pre-chlorination emerges as a critical factor to consider in enhancing coagulation-based algal removal processes.
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Key words:
- surface-adsorbed organic matter /
- pre-chlorination /
- algal removal /
- coagulation
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