铁盐预混凝对微滤膜污染的影响

针对混凝-微滤工艺, 为优化铁盐预混凝条件及揭示不同凝聚体特性对膜污染的影响, 分析了三氯化铁 (ferric chloride, FC) 和聚合硫酸铁 (polymeric ferric sulfate, PFS) 在不同投加量 (0.1、0.2、0.4、0.6 mmol/L) 和混凝pH (4.5、5.5、6.5、7.5) 条件下对水中天然有机物-腐植酸的去除率和膜污染的影响规律.实验结果表明:当酸性pH 4.5~5.5电性中和机理为主时, PFS低投药量 (0.1~0.2 mmol/L) 凝聚体颗粒大而密实, 膜过滤中通量下降缓慢, 膜污染程度轻, 此时聚铁水解产物的高电荷比单铁更有利于电中和;中性pH 6.5~7.5卷扫混凝时, FC高投药量 (0.4~0.6 mmol/L) 缓解膜污染的作用更明显, 此时单铁水解产物卷扫混凝形成凝聚体的颗粒粒径更大.可见, 混凝凝聚体颗粒大小与结构特性, 是膜污染的直接影响因素, 大而密实的颗粒有利于增加膜通量, 同时提高出水水质.

Influence of Iron Salts Pre-coagulation on Fouling of Microfiltration Membrane

To optimize the iron pre-coagulation condition and clarify the influence of different aggregates characteristics on membrane fouling for coagulation- microfiltration( MF) process, pre-coagulation conditions of ferric chloride( FC) and polymeric ferric sulfate( PFS) at different coagulant dosages( 0. 1,0.2,0.4,0.6 mmol/L) and coagulation pH values( 4.5,5.5,6.5,7.5) were analyzed to reveal membrane fouling mechanisms and humic acid removal. Results show that under acidic pH 4. 5-5. 5 of electrical neutralization coagulation condition,the lower PFS dosage( 0. 1- 0. 2 mmol /L) has the better coagulation effect,which the agglomerates have larger particle size and higher fractal dimension for more high positive charge produced by polymeric ferric hydrolysis products have an advantage in charge neutralization in comparison with FC. Thus membrane flux declination is slowed down and membrane fouling is alleviated. Under neutral pH 6. 5- 7. 5 of sweep coagulation,the higher dosage( 0. 4-0. 6 mmol /L) of FC is superior to reduce membrane fouling,as hydrolysis products of FC is liable to produce larger particles in sweep coagulation. Particle size and structural characteristics of the coagulation agglomerates directly affect the membrane fouling,the larger particle size and higher fractal dimension are superior to increase membrane flux and simultaneously improve water quality.