Formation of disinfection by-products from coexisting organic matter during vacuum ultraviolet (VUV) or ultraviolet (UV) treatment following pre-chlorination and their fates after post-chlorination

Photodegradation of halogenated organic disinfection by-products: Decomposition and reformation

In this study, the photodegradation of 33 different DBPs (trihalomethanes, haloacetic acids, haloacetaldehydes, and haloacetonitriles) and TOX with low pressure UV light and the subsequent reformation of DBPs with chlorine and monochloramine were investigated. Results indicated that photodegradation followed the order of TOI > TOBr > TOCl, and treated surface water with low SUVA254 background did not impact the photodegradation of highly UV susceptible DBPs such as triiodomethane (TIM), diiodobromomethane (DIBM), tribromomethane (TBM). The mass balance results of chloride, bromide and iodide showed that the main photodegradation mechanism of TOBr and TOI was dehalogenation supported by halide releases (i.e., Cl-, Br- and/or I- ion). In addition, the photodegradation removal effect was higher, when brominated DBPs formation was high. Although low pressure UV light effectively removed halogenated organic DBPs, subsequent use of disinfectants (Cl2 and NH2Cl) reformed photodegraded DBPs, and the overall DBPs concentrations were increased, which suggested that the released Br- and I- ions will reform DBPs in distribution systems, with oxidants present or added (e.g., booster chlorination) in distribution systems. This study showed that although UV photodegradation will reduce halogenated organic DBPs in distribution systems, especially more toxic iodinated and brominated DBPs, it will be a more effective technology towards the end of the distribution system or a point of entry solution rather than in distribution system with post-disinfection and residence time.

Integrated estrogenic effects and semi-volatile organic pollutants profile in secondary and tertiary wastewater treatment effluents in North China

Endocrine-disrupting effects on aquatic organisms caused by wastewater discharging have raised extensive concerns. However, the efficiency of various wastewater treatment processes to remove estrogenic activity in effluents and the association with organic micropollutants was not well known. We evaluated the estrogenic activity using a well-characterized in vivo bioassay featuring the Chinese rare minnows (Gobiocypris rarus) and analyzed 886 semi-volatile organic compounds (SVOCs) in effluents from four secondary wastewater treatment plants (SWTP A-D) and a tertiary wastewater treatment plant (TTP E) that utilized various common treatment processes in northern China. The final effluents from SWTPs and TTP E all exhibited estrogenic effects, increasing male fish plasma vitellogenin (VTG) contents and estradiol/testosterone (E₂/T) ratios. Key regulating genes in the male fish liver including vtg1, vtg3, era, erβ, and cyp19a were upregulated. TTP E demonstrated high performance in reducing estrogenic activity in the effluents, with a reduction of 64% in integrative biomarkers of estrogenic response (IBR). UV disinfection at SWTPs removed IBR by 14%- 33%, while ozone disinfection at TTP E did not reduce IBR. Several SVOCs including alkanes, chlorobenzenes, and phthalates, detected at ng/L to µg/L level, significantly correlated with effluent estrogenic activity. Our findings suggest the necessity and the potential means to improve the efficiency of current wastewater treatment approaches to achieve better protection for aquatic organisms against the joint effects of mixtures of various categories of micropollutants in effluents.

Enhancement of optoelectronic properties of layered MgIn 2 Se 4 compound under uniaxial strain, an ab initio study

We argue that tuning the structure of a semiconductor offers abundant scope for use in a number of applications. In this work, by means of comprehensive density functional theory computations, we demonstrated that layered MgIn 2 Se 4 could be a promising candidate for future electronic and optoelectronic technologies. To do this task, we have applied a uniaxial strain in the z-direction. The results show that MgIn 2 Se 4 can support only a - 2.5 % of deformation without losing its dynamical stability. However, we showed that the effect of strain strongly affects the bonding pattern, which tends to increase the bandgap value. Both the charge density and noncovalent interactions were analyzed to understand this behavior. In addition, we saw that the application of non-hydrostatic pressure also enhanced the photocatalytic/optoelectronic performance of the investigated material, offering useful insights into layered MgIn 2 Se 4 for future development in this area.

Degradation of N-nitrosamines and 1,4-dioxane using vacuum ultraviolet irradiation (UV254+185 nm or UV172 nm)

Advanced oxidation processes (AOPs) play a vital role in attenuating contaminants of emerging concern (CECs) during potable water reuse. AOPs are conventionally performed by irradiating with a 254-nm low-pressure (LP) mercury-vapor (Hg) ultraviolet (UV) lamp along with chemical treatment. Compared with UV-C light treatment (200-280 nm), vacuum-UV (V-UV) light treatment (100-200 nm) is advantageous in terms of hydroxyl radical generation without the requirement for chemical treatment. This study assessed the potential of V-UV (172-nm Xe₂ excimer or 185 + 254-nm LP-Hg) lamps on the destruction of two major CECs in potable water reuse, namely N-nitrosodimethylamine (NDMA) and 1,4-dioxane. Direct irradiation using UV_{254 nm} or UV_{185+254 nm} lamps achieved ≥94% removal of N-nitrosamines, including NDMA, at a UV dose of 900 mJ/cm². In contrast, the Xe₂ excimer lamp (UV_{172 nm}) was less effective for N-nitrosamine removal, achieving up to 82% removal of NDMA. The removal of 1,4-dioxane by V-UV lamps at a UV dose of 900 mJ/cm² reached 51% (UV_{172 nm}) and 28% (UV_{185+254 nm}), both of which results were superior to that obtained using a conventional UV_{254 nm} lamp (10%). The addition of hydrogen peroxide during UV_{254 nm} or UV_{185+254 nm} irradiation was found to enhance the removal of 1,4-dioxane, while UV_{172 nm} irradiation without hydrogen peroxide addition still exhibited greater efficiencies than those UV_{254 nm} lamps-based AOPs. Overall, this study demonstrated that the removal of both NDMA and 1,4-dioxane can be successfully achieved using either a UV_{254+185 nm} lamp with hydrogen peroxide or a UV_{172 nm} Xe₂ excimer lamp without hydrogen peroxide.

Mg2TiO4 spinel modified by nitrogen doping as a Visible-Light-Active photocatalyst for antibacterial activity

Nitrogen doped Mg₂TiO₄ spinel, i.e. Mg₂TiO_4-xN_y, has been synthesized and investigated as a photocatalyst for antibacterial activity. Mg₂TiO_4-xN_y demonstrates superior photocatalytic activity for E. coli disinfection under visible light illumination (λ ≥ 400 nm). Complete disinfection of E. coli at a bacterial cell density of 1.0 × 10⁷ CFU mL^-1 can be achieved within merely 60 min. Mg₂TiO_4-xN_y is capable of generating superoxide radicals (^•O₂ ^-) under visible light illumination which are the reactive oxygen species (ROSs) for bacteria disinfection. DFT calculations have verified the importance of nitrogen dopants in improving the visible light sensitivity of Mg₂TiO_4-xN_y. The facile synthesis, low cost, good biocompatibility and high disinfection activity of Mg₂TiO_4-xN_y warrant promising applications in the field of water purification and antibacterial products.

Mg2TiO4 spinel modified by nitrogen doping as a Visible-Light-Active photocatalyst for antibacterial activity

Nitrogen doped Mg₂TiO₄ spinel, i.e. Mg₂TiO_4-xN_y, has been synthesized and investigated as a photocatalyst for antibacterial activity. Mg₂TiO_4-xN_y demonstrates superior photocatalytic activity for E. coli disinfection under visible light illumination (λ ≥ 400 nm). Complete disinfection of E. coli at a bacterial cell density of 1.0 × 10⁷ CFU mL^-1 can be achieved within merely 60 min. Mg₂TiO_4-xN_y is capable of generating superoxide radicals (^•O₂ ^-) under visible light illumination which are the reactive oxygen species (ROSs) for bacteria disinfection. DFT calculations have verified the importance of nitrogen dopants in improving the visible light sensitivity of Mg₂TiO_4-xN_y. The facile synthesis, low cost, good biocompatibility and high disinfection activity of Mg₂TiO_4-xN_y warrant promising applications in the field of water purification and antibacterial products.