The effects of scale inhibitor ATMP in water on nanofiltration

As a kind of advanced water purification technology, nanofiltration (NF) has been widely used in the treatment of water. In the NF process, scale inhibitor such as aminotris (methylenephosphonic acid) (ATMP, H 6 atmp, H 6 L) is commonly added to control scale deposition. However, the impact of ATMP on the separation performance of NF has up to now been unknown. In this study, the impact of ATMP on calcium ion (Ca 2+ ) rejection rate and permeate flux of NF 270 membrane were investigated by permeate experiments with different ATMP concentrations. The results showed that ATMP had a significant impact on Ca 2+ rejection rate, as well as the feed pH. Both a local minimum in rejection rate and a slight maximum in permeate flux appeared at 10 mg·L –1 ATMP, corresponding to the feed pH about 5.5, which may be close to the isoelectric point (IEP) of membrane. When ATMP concentration was below 8 mg·L –1 and above 10 mg·L –1 , increasing ATMP concentration would both dramatically enhance Ca 2+ rejection rate. The main mechanism affecting the performance of NF was electrostatic effect caused by ATMP rather than its chelation effect. Our work demonstrated that in addition to the scale inhibition effect, ATMP in water also had a certain impact on the performance of NF membrane, especially for treating low alkalinity water (contain hardness and SO 4 2- ), and aminotris (methylene phosphonic acid) (ATMP, H 6 atmp, H 6 L) is preferred to avoid precipitation and improve NF softening and desalination performance.