The treatment of wastewater from the textile industry containing organic dyes faces many challenges since these compounds resist the biodegradation process in conventional treatment units. Among the physicochemical processes, photocatalysis is considered a facile, cheap, and environmental-friendly technology for treating persistent organic pollutants in waters at low concentrations. This study investigated several physicochemical factors determining the photocatalytic activity of titanate nanotubes (TNTs) to remove Procion MX 032 (PMX), an azo dye, in waters. Degradation of PMX by photocatalytic oxidation process at room temperature (30°C) was set up with the UV irradiation in the presence of different types of photocatalyst such as ST-01 (100% anatase), industrial TiO2, TNTs calcined at 120°C and 500°C. Effect of reaction time, catalyst amount, pH, light wavelength and intensity, and oxidants was investigated. Consequently, TNTs calcined at 500°C provided the highest removal efficiency. The photocatalytic oxidation of PMX by TNT calcined at 500°C was affected by pH variation, getting the highest removal at pH of 8, and inhibited with the presence of H2O2 and O2. Particularly, the PMX degradation using titanate nanotubes was optimized under the UV-A intensity of 100 W/m2. The dye was degraded by more than 95% at the TNTs concentration of 75 mg/L and pH 8.0 after 90 min. The results suggest that photocatalysis using TNTs can be a simple but efficient treatment method to remove PMX and potentially be applied for the treatment of wastewaters containing dyes.

The reverse osmosis (RO) water desalination system powered by the photovoltaic (PV) unit is commonly used to produce drinking water due to their reasonable price. This review focused to display different designs of small-scale PV powered brackish water RO (PV-BWRO) systems that were installed to improve the water productivity at remote areas. The configuration of BWRO units, which determined the operating cost, permeate flow and amount of rejected water, is of great concerns in this work. The specific energy consumption (SEC), total capital cost and water production cost are also analysed to display the feasibility of application of PV unit for small-scale BWRO desalination system. The single-stage configuration was suitable for most of small-scale BWRO systems owning high recovery rates (i.e., higher than 50%). The PV solar system pairing with batteries was not recommended at production capacities below 5 m3 for their high cost and short lifetime. Independently operated PV-BWRO systems required the highest capital cost while produced the lowest operating and overall production costs compared to hybrid systems.

In natural water, colloidal particles play an important role in the transport of organic compounds, including pollutants. The analysis of colloidal particles creates more bases for the selection of river water treatment technology, making the treatment more efficient. In this study, the size and zeta potential of colloidal particles in Saigon river water were determined. Seven sampling sites were randomly selected along the river length in Ho Chi Minh City. One of the locations was selected to investigate colloidal properties at different times (i.e. 10 samples). The results showed that the colloidal particles have poor stability with Zeta potentials in the range from -19 mV to -12 mV. Besides, statistical analysis showed that the zeta potential had an inverse correlation with the pH value and the permanganate index with the significant coefficients of -0.67 and -0.73, respectively. The size of colloidal particles in water is not uniform; however, due to poor stability, part of the particles join together and settle down. Coagulation-flocculation-sedimentation-rapid sand filtration experiments were also performed to remove colloidal particles from the water. The treated water has low turbidity with a removal efficiency of 97%. This shows that the colloidal particles presented in the Saigon River water could be easily removed by the traditional physicochemical method. However, the parameters of the permanganate index and Coliforms did not meet the standard of QCVN 01-1/2018/BYT for drinking purposes, which still require further treatment.