Forward-osmosis strategy and chemical cleaning of seawater desalination reverse osmosis membranes

doi:10.11949/0438-1157.20200326

Abstract

Abstract:

In order to settle the membrane fouling of reverse osmosis membranes in seawater desalination process, this study reported a novel strategy based on forward-osmosis process and discussed the effects of different factors like different cleaning combination among reverse osmosis product, simulated reverse osmosis concentrate and simulated seawater, as well as cleaning time on the membrane permeate flux and salt rejection. For irreversible fouling, the effects of different chemical cleaning agents, immersion time and concentration were also investigated in this study. The results exhibited that the cleaning combination between diluted water and simulated reverse osmosis concentrate possessed the best cleaning performance in the process of forward-osmosis cleaning. Such approach also enhanced normalized flux from 9.48 L/(m²·h·MPa) to 13.6 L/(m²·h·MPa) and enhanced NaCl rejection from 80.59% to 92.80%. Furthermore, the normalized flux was enhanced from 9.48 L/(m²·h·MPa) to 14.3 L/(m²·h·MPa) and NaCl rejection was also enhanced from 80.59% to 96.27% after soaking in 2%(mass) citric acid solution for 2h, soaking with 1%(mass) ethylenediamine tetra-acetic acid tetrasodium salt and 0.3%(mass) sodium tripolyphosphate solution for 1.5 h. According to the result of SEM images and AFM images, the forward-osmosis cleaning strategy could not cause the damage of selective layer of membrane surface and caused the drop of inorganic and organic fouling on the membrane surface. Hence, cleaning fouled RO membranes by such approach could prolong the chemical cleaning cycle and reduce the amount of chemical cleaning agent, which has certain industrial application perspectives.

Key words: membrane, separation, desalination, forward-osmosis cleaning, seawater desalination, reverse osmosis

摘要：

为解决海水淡化过程中反渗透膜的污染问题，研究了基于正渗透策略的反渗透产水、模拟反渗透浓水、模拟海水不同的组合清洗和清洗时间对膜通量和截留率的影响。针对不可逆污染，研究了不同化学清洗药剂、浸泡时间、浓度对膜通量和截留率的影响。结果表明，正渗透策略清洗方式中，淡水/模拟反渗透浓水的组合清洗方式效果最佳，其归一化通量从9.48 L/(m²·h·MPa)提升至13.6 L/(m²·h·MPa)，截留率从80.59%提升至92.80%。此外，经质量分数为2%的柠檬酸溶液浸泡2 h后，再使用质量分数为1%的乙二胺四乙酸四钠盐和0.3%的三聚磷酸钠溶液浸泡1.5 h，其归一化通量从9.48 L/(m²·h·MPa)提升至14.3 L/(m²·h·MPa)，截留率从80.59%提升至96.27%。从SEM和AFM图可以看出，正渗透清洗策略并未对膜表面选择层造成损坏，且可以清洗膜表面的有机污染物和无机污染物，因此，应用这种方法对污染的反渗透膜进行清洗，可延长化学清洗周期，减少化学清洗剂用量，具有一定的工业应用前景。

关键词: 膜, 分离, 脱盐, 正渗透清洗, 海水淡化, 反渗透

CLC Number:

TQ 028.8

Ming TAN, Wenguang WANG, Xiaodong ZHANG, Hongwu ZHAO, Yang ZHANG, Xingtao YANG. Forward-osmosis strategy and chemical cleaning of seawater desalination reverse osmosis membranes[J]. CIESC Journal, 2020, 71(S2): 306-313.

谭明, 王文广, 张晓东, 赵洪武, 张杨, 杨兴涛. 正渗透策略和化学清洗海水淡化反渗透膜[J]. 化工学报, 2020, 71(S2): 306-313.

Figures/Tables 12

Fig.1 Homemade reverse osmosis membrane cleaning apparatus

Fig.2 Relationship among normalized flux, rejection and cleaning time

Fig.3 Relationship among normalized flux, rejection and cleaning time

Fig.4 Relationship among normalized flux, rejection and cleaning methods

Table 1 Effects of citric acid concentration and soaking time on normalized flux

浸泡时间/h	归一化通量
浸泡时间/h	2%柠檬酸	3%柠檬酸	4%柠檬酸
0	9.48±0.17	9.48±0.17	9.48±0.17
1	7.81±0.09	9.41±0.02	7.23±0.05
1.5	7.72±0.01	9.79±0.05	6.75±0.01
2	7.57±0.01	10.43±0.05	6.16±0.08

Table 2 Effects of citric acid concentration and soaking time on NaCl rejection

浸泡时间/h	NaCl截留率/%
浸泡时间/h	2%柠檬酸	3%柠檬酸	4%柠檬酸
0	80.21	80.21	80.21
1	79.42	76.64	77.61
1.5	85.83	75.67	84.89
2	86.52	74.37	83.56

Table 3 Effects of tripolyphosphate concentration and soaking time on normalized flux

浸泡时间/h	归一化通量
浸泡时间/h	1%EDTA四钠盐、 0.1%三聚磷酸钠	1%EDTA四钠盐、 0.2%三聚磷酸钠	1%EDTA四钠盐、 0.3%三聚磷酸钠
0	9.48±0.17	9.48±0.17	9.48±0.17
1	12.65±0.09	12.64±0.03	11.97±0.09
1.5	16.53±0.02	15.22±0.03	14.30±0.03
2	15.50±0.02	14.94±0.03	15.20±0.06

Table 4 Effects of tripolyphosphate concentration and soaking time on NaCl rejection

浸泡时间/h	NaCl截留率
浸泡时间/h	1%EDTA四钠盐、 0.1%三聚磷酸钠	1%EDTA四钠盐、 0.2%三聚磷酸钠	1%EDTA四钠盐、 0.3%三聚磷酸钠
0	80.59%	80.59%	80.59%
1	87.32%	90.40%	93.15%
1.5	94.07%	94.99%	96.27%
2	91.81%	92.83%	95.29%

Fig.5 AFM micrographs of membranes after cleaning with different methods

Fig.6 SEM images of membranes after cleaning with different methods

Fig.7 IR spectra of membranes after cleaning with different methods

Fig.8 Zeta potential of RO membranes after cleaning with different methods

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