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膜污染问题已成为限制膜分离效率的主要瓶颈[1],并显著提高了运行和维护成本[2]。通常,需要采用预处理技术来缓解膜污染。国内外常采用的预处理技术主要包括混凝[3]、吸附[4]、氧化预处理[5]、化学沉淀预处理[6]、生物预处理[7]以及多种技术的组合[8-9]。然而,这些预处理技术需要额外添加化学药剂且具有处理的选择性,这显著增加了膜分离工艺的维护成本[10]。电絮凝作为一种高效的水处理技术,具有操作简单、产泥量小、避免使用化学药品、易实现自动化和设备化控制等优点[11-12]。电絮凝(electrocoagulation, EC)组合膜分离技术,是一种不依赖于化学药剂的水处理方法[13-14]。该技术具有清除膜表面沉积污染物的能力,并且具备操作简便的特点[15-16]。电絮凝是有效减轻膜污染的处理工艺[17-18]。在EC中,通过优化电化学参数,可以调节原位生成的铝(Al)絮体的尺寸,从而减轻膜孔堵塞引起的膜污染问题[19-20],且电絮凝形成的氢氧根水解产物可以和污染物聚集形成较大絮凝体而无法对膜孔造成堵塞,对膜污染具有明显控制作用[21-22]。
电絮凝过程中存在的极板钝化问题,会导致电流效率下降以及运行成本不断升高。通过采用脉冲电源替代直流电源,利用脉冲电流进行电絮凝反应是缓解电极钝化的有效手段。已有研究表明,脉冲电絮凝工艺中极板的实际通电时间小于电絮凝处理的总反应时间有助于减少污染物在极板表面的沉积进一步缓解电极钝化,高效去除废水中的污染物[23-24]。在ECMCR(electrocoagulation-membrane cathode reactor, ECMCR)中,牺牲的Fe/Al阳极产生Fe/Al离子以凝固胶体和有机物,这可以通过改善滤饼层结构来增强膜分离效率并减轻膜污染[25]。在电场混凝和HA-Al絮凝极化的综合作用下,将电絮凝和超滤膜组件集成到一个单元中进一步改善了滤饼层结构[26]。如果采用脉冲电源,可以降低ECMCR中电极钝化,提高电流效率、降低能耗。脉冲电絮凝在污水治理中得到了广泛的应用,EYVAZ[27]等使用利用脉冲电絮凝法去除水中染料的影响进行了探究,脉冲电絮凝可以克服直流电絮凝的局限,通过使用脉冲电来消除阴极钝化,发现使用脉冲电絮凝可以节省能耗并提高染料的去除效率。张洁培[28]利用脉冲电絮凝去除聚乙烯醇(PVA),研究发现脉冲电絮凝对PVA去除效果更加明显,去除率可达90%以上,而直流电絮凝对PVA去除很难进一步提高,在相同的去除效率下,脉冲电絮凝的电极损耗比直流电絮凝降低了26.6%,脉冲电絮凝的能耗比直流电絮凝降低89.8%。刘方圆[29]针对传统电絮凝处理含Cr(VI)废水所产生的极板钝化、能耗以及污泥量等问题,提出引入脉冲电流来对传统电絮凝处理过程中所遇到的问题进行优化,实验发现,在达到相似去除率的前提下,与直流电絮凝相比,单脉冲电絮凝可以节省能耗89%,污泥量减少30%,双脉冲电絮凝比直流电絮凝节能80%,污泥量减少39%。从能耗考虑,单脉冲电絮凝是去除Cr(VI)的最佳选择;从污泥减量考虑,双脉冲电絮凝是去除Cr(VI)的最佳选择。罗皓鹏[30]研究APC-EC脉冲电絮凝工艺各工作参数对于实际处理效果的影响,分析比较确定其在饮用水方面的最佳工作参数,研究表明脉冲电絮凝在处理实际水体的成本上面却只有传统电絮凝工艺的44.22%,脉冲电絮凝去除阿特拉津和氟离子的效率相较于直流电絮凝分别提高了7%和13.94%。现有的研究主要集中在利用脉冲的方式提高电絮凝污染物去除效率,但脉冲电絮凝对于膜污染的控制效果尚不清楚,而解析电场对于滤饼层结构的调控作用是脉冲电絮凝与膜分离耦合的关键。
本研究通过建立了新型脉冲电絮凝-膜分离反应器(pulsed electrocoagulation-membrane membrane cathode reactor, PECMCR),将导电膜放置于极板中间,通过利用电气浮和极板之间存在的电场作用,减缓膜污染的同时,提高HA去除率。此外,还考察了反应器在相同产铝量和能耗下,PECMCR和ECMCR对HA去除效果、膜污染情况的差异,通过分析絮体尺寸和滤饼层结构来探究其原因并优化不同电流密度、初始pH、不同脉冲频率、不同占空比对PECMCR的影响,确定PECMCR最佳工作条件。本研究为PECMCR在实际工程中的应用奠定了基础并构建一种高效稳定的无药剂水处理技术。
脉冲电絮凝-膜分离反应器的膜污染控制机制
Membrane contamination control mechanism in the pulsed electrocoagulation-membrane separation reactor
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摘要: 为了改进直流电絮凝膜分离反应器(electrocoagulation-membrane cathode reactor, ECMCR)在实际应用中存在极板钝化、能耗高等不足,本研究开发了脉冲电絮凝膜分离反应器(pulsed electrocoagulation-membrane cathode reactor, PECMCR),并分析了其中的膜污染控制机制。研究发现ECMCR对腐殖酸(humic acid, HA)的去除率最高可达85.23%,相比之下相同产铝量和能耗下脉冲电絮凝膜分离反应器对HA的最佳去除效率可达到90%以上,且跨膜压差分别降低了36%和20%。PECMCR相较于ECMCR具有更好的HA去除效果和膜污染缓解效果,这可能是因为在脉冲电场的作用下,金属阳离子在溶液中加速扩散,减少或消除了金属阳极的钝化现象,从而有效提高HA的去除效率。而且HA与膜阴极之间的静电斥力降低了HA污染物在膜上的粘附,有助于进一步缓解膜污染。另外,脉冲电絮凝可以缓解电极钝化,有助于进一步节省能耗。此研究结果为PECMCR应用于水处理过程中膜污染控制提供了新的解决方案。Abstract: In order to improve the shortcomings of DC electrocoagulation-membrane cathode reactor (ECMCR) such as plate passivation and high energy consumption in practical applications, this study developed a pulsed electrocoagulation-membrane cathode reactor (PECMCR) and analyzed the membrane contamination control mechanism in it. It was found that ECMCR could remove humic acid (HA) up to 85.23%, by comparison, the optimal removal efficiency of HA of was higher than 90% by the pulsed electrocoagulation-membrane separation reactor with the same aluminum production and energy consumption, and their trans-membrane differential pressures decreased by 36% and 20%, respectively. PECMCR had better HA removal and membrane contamination mitigation effect compared with ECMCR, which may be attributed to the accelerated diffusion of metal cations in the solution under the action of pulsed electric field, which could reduce or eliminate the passivation phenomenon of the metal anode, and thus could effectively improve the removal efficiency of HA. Moreover, the electrostatic repulsion between HA and the membrane cathode could reduce the adhesion of HA pollutants on the membrane, which was conducive to further alleviating membrane contamination. In addition, pulsed electro-flocculation can alleviate electrode passivation, which was conducive to further saving energy consumption. The results of this study provide a new solution for the application of PECMCR to control membrane contamination in water treatment process.
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Key words:
- humic acid /
- electrocoagulation /
- membrane separation /
- filter cake layer
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表 1 不同反应条件下脉冲与直流滤饼层比表面积、孔容、孔隙率和密度
Table 1. Specific surface area, pore volume, porosity and density of pulsed and DC filter cake layers under different reaction conditions
反应条件 密度/
(g·cm−3)质量/g 体积/cm3 孔容/
(cm3·g−1)比表面积/
(m2·g−1)孔隙率/% 直流电絮凝 2.249 0 0.306 9 0.123 7 0.247 5 72.818 0 50 相同铝量下脉冲电絮凝 2.307 7 0.390 0 0.169 0 0.268 2 84.771 5 63 相同能耗下脉冲电絮凝 2.255 05 0.350 0 0.155 2 0.258 7 86.338 1 60 -
[1] ZHANG H, SUN M, SONG L, et al. Fate of NaClO and membrane foulants during in-situ cleaning of membrane bioreactors: Combined effect on thermodynamic properties of sludge[J]. Biochemical Engineering Journal, 2019, 147: 146-152. doi: 10.1016/j.bej.2019.04.016 [2] CHEN Y, TENG J, LIAO B Q, et al. Molecular insights into the impacts of iron(III) ions on membrane fouling by alginate[J]. Chemosphere, 2020, 242: 125232. doi: 10.1016/j.chemosphere.2019.125232 [3] YAO M, NAN J, CHEN T, et al. Influence of flocs breakage process on membrane fouling in coagulation/ultrafiltration process: Effect of additional coagulant of poly-aluminum chloride and polyacrylamide[J]. Journal of Membrane Science, 2015, 491: 63-72. doi: 10.1016/j.memsci.2015.05.018 [4] 郑武, 于萍. 吸附预处理减缓微滤膜污染试验研究[J]. 四川大学学报:自然科学版, 2018, 55: 1265. [5] 瞿芳术、杨枝盟、周鸿、荣宏伟、赫俊国、余华荣. 高锰酸钾预氧化对高藻水超滤过程中膜污染及锰沉积的影响[J]. 膜科学与技术, 2020, 40(6): 29-36. [6] 杜琦. 化学沉淀—离子交换法处理电镀含镍废水研究[D]. 兰州: 兰州大学, 2020. [7] WANG Y, JU L, XU F, et al. Effect of a nanofiltration combined process on the treatment of high-hardness and micropolluted water[J]. Environmental research, 2020, 182(Mar.): 109063.1-.9. [8] 张静, 吴慧芳, 陈佳琪, 等. 预处理技术对超滤膜污染控制的研究现状[J]. 能源环境保护, 2022, 36(1): 18-22. [9] 聂煜东, 李金, 张贤明. 水处理过程中膜污染问题及其预处理技术研究进展[J]. 化工进展, 2021, 40(4): 2278-2289. [10] 高倩, 张崇淼, 魏样, 等. 饮用水超滤处理中的膜污染及减缓技术研究进展[J]. 中国给水排水, 2020, 36(18): 13-18. [11] 高旭, 李鹏, 王学刚, 等. 絮凝与电絮凝对含铀废水的处理效果对比[J]. 环境工程学报, 2018, 12(2): 488-496. [12] 王思宁, 丁晶, 赵庆良, 等. 电絮凝技术处理高盐废水的研究进展[J]. 黑龙江大学自然科学学报, 2018, 35(1): 72-78. [13] 赵凯, 杨春风, 孙境求, 等. 调控絮体形态强化电絮凝减缓膜污染[J]. 环境科学, 2016, 37(11): 4255-4260. [14] 李梦琦, 杨春风, 赵凯, 等. 电絮凝-膜分离反应器还原-絮凝-超滤一体化处理六价铬废水[J]. 环境工程学报, 2018, 12(1): 79-85. [15] MAGNISALI E D, QUN Y, VAYENAS D V. Electrocoagulation as a revived waste water treatment method-Practical Approaches: A review[J]. Journal of Chemical Technology & Biotechnology, 2022, 97(1): 9-25. [16] SAHU O, MAZUMDAR B, CHAUDHARI P K. Treatment of wastewater by electrocoagulation: a review[J]. Environmental Science and Pollution Research, 2014, 21(4): 69-71. [17] SARDARI K, FYFE P, LINCICOME D, et al. Combined electrocoagulation and membrane distillation for treating high salinity produced waters[J]. Journal of Membrane Science, 2018, 564: 82-96. doi: 10.1016/j.memsci.2018.06.041 [18] HARIF T, HAI M, ADIN A. Electroflocculation as potential pretreatment in colloid ultrafiltration[J]. Water Supply, 2006, 6(1): 69-78. doi: 10.2166/ws.2006.008 [19] HARIF T, KHAI M, ADIN A. Electrocoagulation versus chemical coagulation: Coagulation/flocculation mechanisms and resulting floc characteristics[J]. Water Research, 2012, 46(10): 3177-3188. doi: 10.1016/j.watres.2012.03.034 [20] ROA-MORALES G, CAMPOS-MEDINA E, AGUILERA-COTERO J, et al. Aluminum electrocoagulation with peroxide applied to wastewater from pasta and cookie processing[J]. Separation and Purification Technology, 2007, 54(1): 124-129. doi: 10.1016/j.seppur.2006.08.025 [21] 乔波, 段谟华, 刘芬, 等. 在线反冲下电絮凝对可逆及不可逆膜污染的影响[J]. 水处理技术, 2019, 45(5): 76-81. [22] 周振, 姚吉伦, 庞治邦, 等. 电絮凝延缓陶瓷微滤膜污染[J]. 环境工程学报, 2016, 10(5): 2279-2283. [23] WANG J, YAO J, WANG L, et al. Multivariate optimization of the pulse electrochemical oxidation for treating recalcitrant dye wastewater[J]. Separation and Purification Technology, 2020, 230: 115851. doi: 10.1016/j.seppur.2019.115851 [24] KARAMATI-NIARAGH E, ALAVI MOGHADDAM M R, EMAMJOMEH M M, et al. Evaluation of direct and alternating current on nitrate removal using a continuous electrocoagulation process: Economical and environmental approaches through RSM[J]. Journal of Environmental Management, 2019, 230: 245-254. [25] SOEPRIJANTO, PERDANI A D, NURY D F, et al. Treatment of oily bilge water by electrocoagulation process using aluminum electrodes[J]. AIP Conference Proceedings, 2017, 1840(1): 110015. [26] YU B, SUN J, ZHAO K, et al. Mitigating membrane fouling by coupling coagulation and the electrokinetic effect in a novel electrocoagulation membrane cathode reactor[J]. Water Research, 2022, 217: 118378-. doi: 10.1016/j.watres.2022.118378 [27] EYVAZ M, KIRLAROGLU M, AKTAS T S, et al. The effects of alternating current electrocoagulation on dye removal from aqueous solutions[J]. Chemical Engineering Journal, 2009, 153(1): 16-22. [28] ZHANG J, LI J, MA C, et al. High-efficiency and energy-saving alternating pulse current electrocoagulation to remove polyvinyl alcohol in wastewater[J]. RSC Advances, 2021, 11(63): 40085-40099. doi: 10.1039/D1RA08093H [29] ZHOU R, LIU F, WEI N, et al. Comparison of Cr(VI) removal by direct and pulse current electrocoagulation: Implications for energy consumption optimization, sludge reduction and floc magnetism[J]. Journal of Water Process Engineering, 2020, 37: 101387. doi: 10.1016/j.jwpe.2020.101387 [30] 罗皓鹏. 脉冲电絮凝处理农村微污染饮用水的工艺优化[D]. 哈尔滨: 哈尔滨工业大学, 2021. [31] MüLLER S, BEHRENDS T, VAN GENUCHTEN C M. Sustaining efficient production of aqueous iron during repeated operation of Fe(0)-electrocoagulation[J]. Water Research, 2019, 155: 455-464. doi: 10.1016/j.watres.2018.11.060 [32] OLIVEIRA J T, DE SOUSA M C, MARTINS I A, et al. Electrocoagulation/oxidation/flotation by direct pulsed current applied to the removal of antibiotics from Brazilian WWTP effluents[J]. Electrochimica Acta, 2021, 388: 138499. doi: 10.1016/j.electacta.2021.138499 [33] CHEN Y M, ZHOU B X, LI L H, et al. Application of Pulse Electrocoagulation to Dye Wastewater Treatment[J]. Advanced Materials Research, 2011, 233-235: 444-451. doi: 10.4028/www.scientific.net/AMR.233-235.444