Nitrate removal from contaminated water using polyelectrolyte-enhanced ultrafiltration

The removal of nitrate from contaminated groundwater via polyelectrolyte-enhanced ultrafiltration (UF) was investigated using different chelating polymers and membrane pore sizes. Although the percentage polymer rejection by membranes slightly decreased with higher chelating polyelectrolyte dosages, the nitrate rejection efficiency continued to increase while retaining a larger amount of polymers. Substantial nitrate removal up to >90% at high molar ratios of quaternary amine groups to nitrate was achieved depending on the types of chelating polymers and UF membranes used. The branched polymers removed nitrate better than the linear polymers, whereas the UF membrane with higher molecular weight cut-offs (MWCOs) removed more nitrate than that with smaller ones in the presence of polymers. Greater nitrate rejection using the branched chelating polymer and the membrane with higher MWCO was associated with the sorption of polyelectrolytes onto membrane pores and thereby better removal of nitrate by chelation. The flux decline became severe with increasing the dosage of polymers and the MWCO of the UF membranes, but it had no direct correlation with the molecular weight (MW) of chelating polymers. The regeneration of chelating polymers was successfully carried out with a NaCl solution and greater nitrate rejection was achieved with regenerated chelating polymers. This could be attributed to the irreversible attachment of polymers at the membrane surface during the first UF run. The polymers attached might offer an additional sorption capacity for nitrate.