Ultrafiltration behavior of nitrophenols in the presence of humic substances

Drinking water sources are often exposed to contamination by xenobiotics such as nitroaromatic compounds and pesticides. Their presence, even at comparatively low concentrations, makes water unfit for direct municipal supply. In this work, a series of nitrophenols (NPs) of different acidity and hydrophobicity (e.g. nitrophenols; p-nitrophenol (PNP), 2,4-dinitrophenol (DNP), 3,5-dinitrosalicylic acid (DNSA), 2-methyl-4,6-dinitrophenol (DNOC) and 4-nitrophenyl phosphate disodium salt hexahydrate (NPP)) were selected as major pollutants and the effect of their interaction with natural organic matter (e.g. humic substances) on ultrafiltration process in neutral and acidic pHs were elucidated. All trials were carried out with each nitrophenol (0.05 mM) using hydrophilic composite ultrafiltration membrane and repeated with the same conditions but in the presence of HA (0.1 mg/ml). The efficiency of separation was strongly influenced by kind of nitrophenols, pH of solution and concentration of humic substances. In acidic condition, the rejection was decreased in the presence or absence of HA compared to neutral pH. In both conditions, the rejections of DNP, DNSA and DNOC were increased in HA concentrations around 0.2 mg/ml in neutral and around 0.1 mg/ml in acidic condition. The rejections of NPP in the presence and absence of HA did not change during time in both conditions. The behavior of PNP was different from NPs. In neutral condition, the presence of HA resulted in rejection decline at the early stages of the experiment and was gradually increased in HA concentrations higher than 0.37 mg/ml. In acidic condition the rejection was gradually increased in the solution containing HA. The differences between fluxes with or without the presence of HA for both conditions were negligible for all NPs due to negligible formation of a condensed layer to provide resistance against the passage of water.