Arsenic removal by MF membrane with chemical sludge adsorption and NF membrane equipped with vibratory shear enhanced process

Conventional arsenic removal processes have difficulty removing low concentrations of arsenic ion from water. Therefore, it is very hard to comply with stringent low levels of arsenic, such as below 10 mug/L. So, we have developed two arsenic removal processes which are able to comply with more stringent arsenic regulations. They are the MF membrane process combined with chemical sludge adsorption and NF membrane process equipped with the vibratory shear enhanced process (VSEP). In this paper, we examine the performance of these new processes for the removal of arsenic ion of a low concentration from water. We found that chemical sludge produced in the conventional rapid sand filtration plants can effectively remove As (V) ions of H2AsO4- and HAsO42- through anion exchange reaction. The removal efficiency of MF membrane process combined with chemical sludge adsorption increased to about 36%, compared to MF membrane alone. The strong shear force on the NF membrane surface produced by vibration on the VSEP causes the concentration polarization layer to thin through increased back transport velocity of particles. So, it can remove even dissolved constituents effectively. Therefore, As (V) ions such as H2AsO4- and HAsO42- can be removed. The concentration of As (V) ions decreased from 50 mug/L to below 10 mug/L and condensation factor in recirculating water increased up to 7 times by using NF membrane equipped with VSEP.