Facile prepared ball-like TiO2 at GO composites for oxytetracycline removal under solar and visible lights.

With the widespread use of oxytetracycline (OTC), residual OTCs have been detected in natural surface waters, as well as in water and wastewater treatment systems. Semiconductor photocatalysis has been proven to be a green and high-performing method for the removal of organic contaminants. However, most photocatalysts are only effective when irradiated by UV light. This study explores the efficiency of a new semiconductor photocatalysis method for OTC removal under solar and visible light. To expand the spectral range from the UV to the visible region, a facile prepared ball-like TiO2 at graphene oxide (TiO2@GO) composite, a TiO2-associated catalyst, was synthesized. Chemical characterization indicated that the TiO2@GO has the features of both TiO2 and GO, with the regular TiO2 fiber balls cladded by GO nanosheets. The photocatalytic activity of TiO2@GO composites under solar and visible light was evaluated in terms of OTC degradation. Values of 100% and 90% OTC removal efficiencies were achieved with TiO2@GO at 6 mg/L under solar and visible light irradiation, respectively. The band structure of TiO2@GO expanded the spectral range to full light wavelengths, facilitating formation of a light-induced electron hole (h+), which was identified in this study as the major cause of OTC degradation. The pH and TSS levels (>100 mg/L) were found to have high and low impacts, respectively, on the removal efficiency of OTC, while natural organic matter (NOM) was found to have an insignificant impact. Furthermore, the degradation of OTC with catalysis by TiO2@GO was verified using two real water samples, and averages of 90% and 75% OTC removal efficiencies were achieved under solar and visible light respectively. The results indicate that the synthesized TiO2@GO composites can provide an effective way of removing toxic organic compounds, including OTC, from the water system.

Disinfection byproduct formation in drinking water sources: A case study of Yuqiao reservoir.

This study investigated the potential formation of disinfection byproducts (DBPs) during chlorination and chloramination of 20 water samples collected from different points of Yuqiao reservoir in Tianjin, China. The concentrations of dissolved organic matter and ammonia decreased downstream the reservoir, while the specific UV absorbance (SUVA: the ratio of UV254 to dissolved organic carbon) increased [from 0.67 L/(mg*m) upstream to 3.58 L/(mg*m) downstream]. The raw water quality played an important role in the formation of DBPs. During chlorination, haloacetic acids (HAAs) were the major DBPs formed in most of the water samples, followed by trihalomethanes (THMs). CHCl3 and CHCl2Br were the major THM species, while trichloroacetic acid (TCAA) and dichloroacetic acid (DCAA) were the major HAA species. Chloramination, on the other hand, generally resulted in lower concentrations of THMs (CHCl3), HAAs (TCAA and DCAA), and haloacetonitriles (HANs). All the species of DBPs formed had positive correlations with the SUVA values, and HANs had the highest one (R2 = 0.8). The correlation coefficients between the analogous DBP yields and the SUVA values in chlorinated samples were close to those in chloraminated samples.

Removal of graphene oxide nanomaterials from aqueous media via coagulation: Effects of water chemistry and natural organic matter.

With the increasing use of graphene oxide (GO) nanomaterials, its possible environmental release and human effects have received much attention. As GO may enter drinking or wastewater treatment systems like other carbonaceous nanomaterials, and have potential impact on human and/or environmental health, its removal efficiency during water treatment is important and requires investigation. In this study, the removal efficiency of GO during water treatment procedure via coagulation was evaluated, and the effects of solution chemistry and natural organic matter on the coagulation-based removal of GO nanomaterials were investigated. The results indicate that the removal efficiency of GO with alum coagulation can reach 80% with 20 mg/L alum dosage at neutral pH, and will not change significantly with higher concentration of alum. The coagulation mechanism and efficiency were strongly affected by the Al species in aqueous phase, which are controlled by pH. Co-existing cations (e.g. Na) may have minimal effect on GO removal efficiency, and the presence of humic acid (HA) suppresses coagulation remarkably at alum concentrations below 40 mg/L. The results from this study provide critical information for predicting the removal efficiency of GO nanomaterials during alum coagulation phase of water treatment procedure.