Molecular level separation of arsenic (V) from drinking water using cationic micelles and ultrafiltration membrane.

摘要

The United States Environmental Protection Agency (U.S. EPA) lowered the maximum contaminant level (MCL) for arsenic from 50 mug/L to 10 mug/L. About 4,000 drinking water treatment systems in the U.S. may require additional treatment technologies for arsenic to comply with the new MCL. The satisfactory removal of arsenic from drinking water is often unattainable using conventional removal processes and new technologies are in need.; A new arsenic treatment process [micellar-enhanced ultrafiltration (MEUF)] which is capable of achieving extremely low arsenic concentrations is presented in this study. The effects of membrane materials, membrane nominal molecular weight cut-off (NMWCO), feed water arsenic concentration, feed water pH, and the presence of co-occuring inorganic solutes (carbonate, phosphate, silicate, and sulfate) have been shown to play a significant role on the efficiency of arsenic (V) removal and the permeate flux. The results proved that with careful design of the MEUF process, a combination of the parameters described above could be used in order to comply with the new MCL. Polyethersulfone (PES) membranes of 5 kDa NMWCO was found to achieve excellent arsenic removals. For most cases, the arsenic concentration was reduced below 1 ppb using 5 kDa PES membranes. Compared to the coagulation-assisted microfiltration (CMF) process, economic analyses based on a fully continuous operation indicated a lower total capital cost (TCC) and a higher operating and maintenance (O&M) cost for the MEUF process using 5 kDa PES membranes. Considering the superior efficiency of the proposed process the cost differentials are marginal at best.; A nonlinear equilibrium model which combines thermodynamic relations, charge balance equations, and material balance equations with the Oosawa two-phase polyelectrolyte theory has also been developed to correlate the binding of arsenic to cationic cetylpyridinium chloride (CPC) micelles in semiequilibrium dialysis (SED) and MEUF. The mathematical model predicts the permeate arsenic concentrations that would be expected in MEUF from the much simpler SED experiments. The predictions of the nonlinear equilibrium model are compared with the experimental results and they are in strong agreement. Therefore, it is a useful tool in optimizing the process parameters or designing the MEUF process.