单段式和两段式纳滤与反渗透膜除砷对比研究

Comparison investigation on arsenic removal with one stage and two-stage nanofiltration & reverse osmosis membranes

分别采用一级单段式和两段式NF与RO膜系统,研究了其对地下水中三价砷(As(Ⅲ))和五价砷(As(Ⅴ))的截留性能与机理、水质影响、预氧化以及膜污染。结果表明:单段式NF/RO膜对电中性As(Ⅲ)的截留率均较低,分别小于30%和56%,而对As(Ⅴ)截留率均较高,分别大于80%和95%,电荷排斥机理显著。次氯酸钠预氧化As(Ⅲ),总砷的截留效率得到有效提高。原水中共存离子、pH对NF膜截留As(Ⅴ)的影响较大,对RO影响较小。在相同的操作条件下,两段式NF/RO膜较单段式的NF/RO膜对砷的截留性能基本保持稳定,而膜通量和系统回收率均有明显提高,NF膜更理想。ESEM/EDS分析得出,膜表面污染物以钙盐结晶体为主,化学清洗可使膜系统性能得到恢复,NF膜可完全恢复。

One stage and two-stage membrane systems with nanofiltration（NF）and reverse osmosis（RO）membrane were employed to study the removal of arsenic（As（Ⅲ）and As（Ⅴ）） from groundwater and the influence from the influent quality,the pre-oxidation method,and the membrane fouling.Results showed that one stage NF/RO demonstrated low As（Ⅲ）rejection rates（less than 30%and 56% respectively）but both gave better performances for As（Ⅴ）removal（more than 95% and 80% respectively）,where Donnan exclusion played a main role.The total arsenic rejection rate was prominent increased with NaClO pre-oxidation As（Ⅲ）to As（Ⅴ）.Co-existing ions and pH values gave prominently negative effect on NF while insignificant effect on RO in As（Ⅴ）removal.With the stable rejection performance,prominent improvement with the permeate flux and conversion rate was seen in the two-stage system,where NF presented the better characteristic.ESEM/EDS demonstrated that the main fouling components were calcium compounds.The membrane performances could be recovered,especially for NF,by chemical cleaning method.