Natural organic matter (NOM) is defined as a complex matrix of organic materials present in all surface, ground, and soil waters [1]. The presence of NOM, mainly humic substances (HS) in surface waters, constitutes the main route for the absorbance of solar energy in aquatic systems through which a series of photophysical and photochemical processes occur. Humic acid (HA) accounts for a significant fraction of the HS.The presence of HA in aqueous solutions is not directly toxic but could lead to organic disinfectant by-products (DBPs), which are undesired and hazardous products in water treatment after disinfection [2][3]. Furthermore, the high HA concentration in drinking water has the potential for some serious diseases, such as stomach cancer [4][5]. Thus, the presence of HA can be the cause of many problems, and their removal from water is a priority task [6] and has been attempted in different ways. Several processes have been attempted to remove HA from water such as coagulation [7-9], electrocoagulation (EC) [4,[10][11][12][13][14][15], electro-oxidation (EO) [16], ion exchange [17], membrane filtration [18-20], activated carbon adsorption and advanced oxidation processes [21-29]. AbstractRecently, the photocatalytic degradation technique with titanium dioxide (TiO 2 ) has been widely applied for the degradation of humic acid (HA) from aqueous solution due to its ability to achieve complete mineralization of organic contaminants. Because TiO 2 is the most commonly used semiconductor photocatalyst, efforts on the modification of TiO 2 in order to improve catalyst efficiency were presented in this review manuscript. The key photoreactor operation parameters such as TiO 2 loading, pH, temperature, oxygen concentration, concentration and nature of HA, light wavelength, light intensity, the presence of inorganic ions and mechanistic pathway for pollutant removal, and the formation of the intermediates and their effects on the mineralization and disinfection of the photo-process were also assessed. Although we can see an increase in the number of papers that have been published in this area, further progress is needed to improve the understanding of the dynamic interactions between TiO 2 photocatalytic oxidation process and HA, as well as to suggest possible future developments in this promising field.

The use of computational fluid dynamics (CFD) to predict internal and external flows has risen dramatically in the past decade. This research aims to use the commercial software, ANSYS Fluent V.14.5, to illustrate the effects of the rudder and blade pitch on the hydrodynamic performance of the marine propeller by experimenting with propellers and rudders of the M/V Tan Cang Foundation ship, which has designed conditions as follows: diameter of 3.65 m; speed of 200 rpm; average pitch of 2.459 m; boss ratio of 0.1730. Using CFD, the characteristic curves of the marine propeller and some important results showed that the maximum efficiency of the propeller is 0.66 with the open water propeller and 0.689 with the rudder‒propeller system at the advance ratio of 0.6. The obtained outcomes of this research are a significant foundation to calculate and design an innovative kind of propulsion for ships with high performance.

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Humic substances are among the most important natural organic matters (NOM) existing in ground and surface waters and are known as one of the main disinfection by-product (DBPs) precursors that may act as health risk factors [1]. Humic substances -mainly humic acids (HA), which constitute the major fraction of NOM in water supplies -have been suggested as a standard for mimicking NOM in the laboratory. HA are non-biodegradable and have color, odor, and also exhibit a wide range of distribution in molecular weight and Pol. J. Environ. Stud. Vol. 27, No. 6 (2018), 2765-2774 AbstractA photocatalyst comprised of strontium-doped TiO 2 coated on porous ceramic filter media (Sr-TiO 2 /PCFM) was prepared using the heat-treated process. The main objective of this study was to investigate the effects of catalyst dosage, initial HA concentrations, pH, and temperature on the adsorption and degradation of humic acid (HA) in a solution containing Sr-TiO 2 /PCFM under irradiation of UV light. Removal efficiency of 84.25% for HA was achieved under experimental conditions for a Sr-TiO 2 /PCFM dosage of 80 g at an initial concentration of 15 mg/L over a period of 8 h. Higher degradation was found for HA in the acidic environment and at higher operating temperatures. The rate of the adsorption reaction followed the pseudo second-order kinetics with the sorption isotherm well fitted to the Freundlich and Langmuir isotherm models. The oxidation rate constants of HA were evaluated by using pseudo first-order kinetics that can describe the photodegradation process. Furthermore, the photocatalytic stability of Sr-TiO 2 /PCFM was performed with 3 cycles reused. These findings suggest that the Sr-TiO 2 /PCFM was found to be an effective and promising approach to eliminating HA in water resources.

This research is the first report on the purification of domestic wastewater in respect to the application of strontium-doped TiO 2 coated on porous ceramic filter media (Sr-TiO 2 /PCFM) in eight laboratory-scale vertical flow constructed wetlands under irradiation of UV light. All the major pollutant parameters of wastewater were investigated. The online parameters showed that the decrease of dissolved oxygen (DO) reached 68.89% and in the constructed wetlands group which had the Sr-TiO 2 /PCFM material and had a certain anti-clogging ability. By the presence of photocatalyst Sr-TiO 2 /PCFM material, the removal efficiency of COD reached over 80% and eventually stabilized at a higher level (over 71%). Besides that, the Sr-TiO 2 /PCFM material in constructed wetlands improved the average removal efficiency of total phosphorus (TP), total nitrogen (TN), NH 4 +-N, total suspended solids (TSS), and turbidity by 60.89%, 34.89%, 41.87%, 21.10%, and 36.85%, respectively. With Sr-TiO 2 /PCFM material, under the irradiation of UV light, the overall removal efficiency of organic matter removal in terms of dissolved organic carbon (DOC) was 52% in 4 h, which was the best compared with other constructed wetland groups. The results of this study may in turn support improved testing and better optimization of constructed wetland systems for wastewater treatment.