Effect of Re-flocculation of coagulant on ultrafiltration and reverse osmosis membrane system

doi:10.19965/j.cnki.iwt.2021-1223

Abstract

Abstract:

When PAC is used as coagulant for surface water pretreatment，excessive use of coagulant often leads to coagulant pollution in double membrane system. The research results showed that under the condition of pH lower than 6.5，the dosage of PAC 15 mg/L，not complete aluminum ion hydrolysis，the residual aluminum ion concentration in raw water could reach 0.3 mg/L. However， in ultrafiltration and reverse osmosis treatment system，re-flocculation often occurred when the overall hydraulic retention time was greater than 2 h. At the same time，aluminum salt flocs reacted with reverse osmosis scale inhibitor and deposit on the reverse osmosis membrane surface，which directly affected the normal operation of the double membrane system. Therefore，reasonably controlling the dosage of coagulant，adjusting pH and controlling the hydraulic retention time of the system could effectively inhibit the re-flocculation of coagulation and prevent ultrafiltration and reverse osmosis membrane pollution.

Key words: surface water, double membrane system, aluminum ion, re-flocculation, membrane fouling

摘要：

采用PAC作为地表水预处理的混凝剂时，过量地使用混凝剂常常导致双膜系统的混凝剂污染。研究发现，当pH低于6.5，PAC投加量为15 mg/L时，铝离子水解不彻底，原水中残留的铝离子质量浓度可达到0.3 mg/L。而在超滤反渗透处理系统中，总体水力停留时间（HRT）大于2 h时常出现后絮凝现象。同时，铝盐絮体与反渗透阻垢剂发生交联反应，沉积到反渗透膜面，直接影响双膜系统的正常运行。因此合理地控制混凝剂投加量、调节pH、控制系统HRT等可有效抑制混凝的后絮凝现象，防止超滤反渗透膜的污染。

关键词: 地表水, 双膜系统, 铝离子, 后絮凝, 膜污染

CLC Number:

X703.1

Jun YANG, Jie ZHOU, Nan ZHANG, Haibo XU. Effect of Re-flocculation of coagulant on ultrafiltration and reverse osmosis membrane system[J]. Industrial Water Treatment, 2022, 42(9): 155-159.

杨军, 周婕, 张楠, 徐海波. 混凝剂后絮凝对超滤反渗透膜系统影响的研究[J]. 工业水处理, 2022, 42(9): 155-159.

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URL: https://www.iwt.cn/EN/10.19965/j.cnki.iwt.2021-1223

https://www.iwt.cn/EN/Y2022/V42/I9/155

Figures/Tables 8

Table 1 Surface water quality parameters

水质指标	pH	SS/（mg·L^-1）	碱度/（mmol·L^-1）	硬度/（mg·L^-1）	浊度/NTU	电导率/（μS·cm^-1）	Al³⁺/（mg·L^-1）	Ca²⁺/（mg·L^-1）	HCO₃ ^-/（mg·L^-1）	温度/℃	TOC/（mg·L^-1）
数值	7.50	5.5	1.62	240	10	1 100	0.15	72.3	102.6	24.3	2.6

Table 2 Effects of different PAC dosage on effluent quality

PAC投加量/（mg·L^-1）	浊度/NTU	浊度去除率/%	TOC/（mg·L^-1）	TOC去除率/%
2	3.50	65	2.12	18.46
5	2.40	76	1.63	37.31
10	2.30	77	1.68	35.38
15	2.50	75	1.57	39.62

Fig. 1 Effect of PAC dosage on ultrafiltration and reverse osmosis operating pressure

Fig. 2 Effect of adjusting pH on residual concentration of aluminum ion in supernatant

Fig. 3 Effect of different GT values on residual aluminum concentration

Fig. 4 Number of alunite particles under different hydraulic retention time and coagulant dosage

Fig. 5 Variation trend of reverse osmosis differential pressure under different PAC dosage

Fig. 6 Composition analysis of scale sample of reverse osmosis membrane module

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