Applying ultraviolet/persulfate (UV/PS) pre-oxidation for controlling ultrafiltration membrane fouling by natural organic matter (NOM) in surface water.

Membrane fouling is a recognized obstacle for the application of ultrafiltration (UF) for drinking water treatment. In this study, ultraviolet/persulfate (UV/PS) oxidation was employed as a pretreatment to control membrane fouling caused by natural organic matter (NOM) in surface water. The effects of UV/PS pretreatment on amounts and characteristics of NOM were investigated in terms of dissolved organic carbon, fluorescent spectrum, molecular weight distribution and hydrophobicity. UF membrane fouling during filtration of raw and pre-oxidized water was compared with transmembrane pressure development, and the fouled membranes were further characterized using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results indicate that NOM was considerably degraded and partially mineralized (∼58%) by UV/PS pretreatment at a PS dose not exceeding 0.6 mM and a UV irradiation time within 120 min, which was attributed to the generation of sulfate and hydroxyl radicals. The fluorescent compounds in NOM were almost completely degraded (>98%) by the UV/PS pretreatment at a PS dose of 0.4 mM, except for tyrosine-like proteins (∼80%). Moreover, UV/PS pretreatment decreased the ratio of macromolecular compounds and increased the hydrophilic fractions, resulting in reduced NOM adhesion to the membrane. Hence, irreversible fouling by NOM was significantly retarded (∼75%) by the UV/PS pretreatment due to reduction in NOM, and more importantly by preferential degradation of fluorescent, macromolecular and hydrophobic compounds. Fouling control performance was considerably improved at increased PS doses and extended UV irradiation time.

Transformation of triclosan to 2,8-dichlorodibenzo-p-dioxin by iron and manganese oxides under near dry conditions.

Triclosan (TCS) is a broad-spectrum antibacterial agent widely used in household and personal care products and is frequently detected in the environment. Previous studies have shown that TCS could be converted to the more toxic compound 2,8-dichlorodibenzo-p-dioxins (2,8-DCDD) in photochemical reactions and incineration processes. In this study, we demonstrated the formation of 2,8-DCDD from the oxidation of TCS by α-FeOOH and a natural manganese oxides (MnOx) sand. Experiments at room temperature and under near dry conditions showed that Fe and Mn oxides readily catalyzed the conversion of TCS to 2,8-DCDD and other products. Approximately 5.5% of TCS was transformed to 2,8-DCDD by α-FeOOH in 45 d and a higher conversion percentage (6.7%) was observed for MnOx sand in 16d. However, the presence of water in the samples significantly inhibited the formation of 2,8-DCDD. Besides 2,8-DCDD, 2,4-dichlorphenol (2,4-DCP), 4-chlorobenzene-1,2-diol, 2-chloro-5-(2,4-dichlorophenoxy)benzene-1,4-diol, and 2-chloro-5-(2,4-dichlorophenoxy)-1,4-benzoquinone were identified in the reactions. The possible pathways for the formation of reaction products were proposed. This study suggests that Fe and Mn oxides-mediated transformation of TCS under near dry conditions might be another potential pathway for the formation of 2,8-DCDD in the natural environment.