强化混凝/超滤组合工艺膜清洗技术的研究

Cleaning of Membrane in Combined Process of Enhanced Coagulation and Ultrafiltration

强化混凝/超滤技术在去除浊度及有机物等方面具有一定优势,但膜污染造成的性能下降阻碍了其进一步发展。膜清洗能够在一定程度上缓解膜污染、提高膜通量、恢复膜的过滤性能。以湖水为原水,进行强化混凝/超滤试验,考察了物理清洗和化学清洗对膜污染的去除效果。物理清洗以清洗时间为变量,采用先气冲、后水冲的方式;化学清洗以草酸和NaOH为清洗剂,比较不同的组合及清洗条件下的清洗效果。试验结果表明:水力清洗能在一定程度上改善及维持膜通量,清洗后通量上升的比例为50.6%;延长水力清洗时间及在过滤和清洗过程中增加曝气,均有助于通量的恢复。化学清洗后扫描电镜(SEM)的分析结果表明,当以三氯化铁为混凝剂时,采用2%的草酸溶液浸泡40 min后,对膜表面污染的去除效果较好,而先采用2%的草酸溶液浸泡40 m in,再用2%的NaOH溶液反冲30 min,对膜孔内污染的清洗效果相对较好。

The combined process of enhanced coagulation and ultrafiltration offers higher efficiency in removing turbidity and natural organic matters, but the decline of membrane performance caused by fouling hinders its further development. The cleaning can mitigate membrane fouling, improve membrane flux and recover membrane filtration performance to some extent. The effect of physical and chemical cleaning of membrane fouled by the lake water after enhanced coagulation and uhrafiltration was investigated. During the physical cleaning, backwashing with air and then water was adopted, and the cleaning time was the only variable. During the chemical cleaning, oxalic acid and sodium hydroxide were used as the cleaning agents. The cleaning efficiencies of different cleaning agents and conditions were compared. The experiment results show that hydraulic cleaning can improve and maintain the membrane flux, and the ratio of flux recovery obtained after cleaning is 50.6%. A longer cleaning time or addition of aeration during filtration and backwashing can improve the flux. SEM after chemical cleaning indicates that when ferric chloride is used as coagulant, after soaked in solution of 2% oxalic acid for 40 min, the removal ef- ficiency of foulants on the membrane surface is better. After soaked in 2% oxalic acid for 40 rain and then backwashing with sodium hydroxide for 30 min, the cleaning efficiency of membrane pores is better.