Formaldehyde degradation by UV/TiO_2/O_3 process using continuous flow mode

The degradation of formaldehyde gas was studied using UV/TiO2/O3 process under the condition of continuous flow mode. The effects of humidity, initial formaldehyde concentration, residence time and ozone adding amount on degradation of formaldehyde gas were investigated. The experimental results indicated that the combination of ozonation with photocatalytic oxidation on the degradation of formaldehyde showed a synergetic action, e.g,, it could considerably increase decomposing of formaldehyde. The degradation efficiency of formaldehyde was between 73.6% and 79.4% while the initial concentration in the range of 1.84--24 mg/m^3 by O3/TiO2flJV process. The optimal humidity was about 50% in UV/TiO2/O3 processs and degradation of formaldehyde increases from 39.0% to 94.1% when the ozone content increased from 0 to 141 mg/m^3. Furthermore, the kinetics of formaldehyde degradation reaction could be described by Langmuir-Hinshelwood model. The rate constant k of 46.72 mg/（m^3.min） and Langmuir adsorption coefficient K of 0.0268 m^3/mg were obtained.

Photolysis pathway of nitroaromatic compounds in aqueous solutions in the UV/H_2O_2 process

Nitroaromatic compounds such as nitrobenzene and nitrophenols are largely synthesised and particularly often occur in water bodies as toxic pollutants. The degradation of these compounds in the environment via direct photolysis and by biological treatment is difficult and usually slow. In our two previous published papers, we have discussed the advanced oxidation of nitrobenzene and nitrophenols in aqueous solutions irradiated by direct photolysis using polychromatic light and by means of UV/H2O2 process. The experimental results suggested the UV/H2O2 process is an effective and efficient technology for complete mineralization of these organic compounds. Based on the results therein, comprehensive reaction mechanism for nitrobenzene photolysis was proposed with detailed discussions.

Photodegradation of nitroaromatic compounds in aqueous solutions in the UV/H_2O_2 process

Photodegradation of nitrobenzene and nitrophenols in aqueous solutions by means of UV/H2 O2 process was studied in the Rayox batch reactors. Three nitrophenol isomers were identified as main photoproducts in the irradiated NB aqueous solutions. The distribution of nitrophenol isomers follows the order p-〉 m-〉 o-nitrophenol. Other intermediates detected include nitrohydroquinone, nitrocatechol, catechol, benzoquinone, phenol, nitrate/nitrite ions, formic acid, glyoxylic acid, maleic acid, oxalic acid and some aliphatic ketones and aldehydes. The degradation of nitrobenzene and nitrophenols at initial stages follows the first-order kinetics and the decay rate constants for nitrobenzene（NB） are around l0^-3-10^-2 s^-1 and for nitrophenols are around 10^-2 s^-1. The decomposition of H2 O2 in the presence of NB and each nitrophenol isomers follows zero-order kinetics. The quantum yields at initial stages for NB decay were estimated around 0.30 to 0.36, and for NPs decay is around 0.31-0.54.

Advanced treatment of oil recovery wastewater from polymer flooding by UV/H_2O_2/O_3 and fine filtration

In order to purify oil recovery wastewater from polymer flooding （ORWPF） in tertiary oil recovery in oil fields, advanced treatment of UV/H2O2/O3 and fine filtration were investigated. The experimental results showed that polyacrylamide and oil remaining in ORWPF after the conventional treatment process could be effectively removed by UV/H2O2/O3 process. Fine filtration gave a high performance in eliminating suspended solids. The treated ORWPF can meet the quality requirement of the wastewater-bearing polymer injection in oilfield and be safely re-injected into oil reservoirs for oil recovery.

Influence of coexisting substances on the photodegradation behaviors of 17α-ethinylestradiol (EE_2) in the UV/H_2O_2 process

The batch photodegradation reactor was used to investigate the influence of the common coexisting substances in wastewater,such as H+,anions (HCO3-,Cl-and NO3-) and organic compounds (methanol and bisphenol A),on the photodegradation behaviors of EE2 in the UV/H2O2 process.The results indicated that the addition of coexisting substances can influence the photodegradation behaviors of EE2 and it also follows the first-order kinetics.The acidic (pH 2-4) and alkaline (pH 10-12) medium benefit the photodegradation of EE2,but the photodegradation rate constant of EE2 keeps almost constant in the pH value of 4-10.The addition of anions,such as HCO3-,Cl-and NO3-,can inhibit the photodegradation of EE2,and the rate constant has a negative linear relationship with the concentration of the anions.However,the reduction degrees vary with the anions kinds,and the inhibition effect of the three anions is in the order of HCO3->NO3->Cl-.Addition of 5 mg/L methanol and bisphenol A can reduce the photodegradation rate constant of EE2by 84.31% and 72%,respectively.By comparison,the retardant effect of methanol is much more evident.In the studied concentrations range,the photodegradation rate constant of EE2 is the unary quadratic function of the organic compounds concentrations.

Decomposition of Benzo （a） Pyrene on Artificial Sea Water Using UV/Photocatalytic Oxidation Process

In recent years, serious heavy oil pollution has frequently occurred in the ocean. Heavy oil has escaped from grounded oil carrier and drifted ashore. Drifted heavy oil contains hazardous chemical such as benzo （a） pyrene and other poly aromatic hydrocarbons （PAHs）. These hazardous chemicals have worse affected on sea plants and animals. Thus, it is important to develop effective elimination of hazardous chemicals or drifted petroleum from sea shore. In this study, we have investigated the decomposition of benzo （a） pyrene on artificial sea water using UV/photocatalytic oxidation process. From this study, it was found that about 90% of benzo （a） pyrene on artificial seawater was decomposed by UV/photocatalytic oxidation process. And there were no by-product from decomposition of benzo （a） pyrene. It was supposed that benzo （a） pyrene was completely decomposed using UV/photocatalytic oxidation process.

Photocatalytic oxidation of nitric oxide from simulated flue gas by wet scrubbing using ultraviolet/TiO_2/H_2O_2 process

Nitric oxide(NO) from flue gas is hard to remove because of low solubility and reactivity. A new technology for photocatalytic oxidation of NO using ultraviolet(UV)/TiO2/H2O2 process is studied in an efficient laboratory-scale reactor. Effects of several key operational parameters on NO removal efficiency are studied, including TiO2 content, H2O2 initial concentration, UV lamp power, NO initial content, oxygen volume fraction and TiO2/H2O2 solution volume. The results illustrate that the NO removal efficiency increases with the increasing of H2O2 initial concentration or UV lamp power. Meanwhile, a lower NO initial content or a higher TiO2/H2O2 solution volume will result in higher NO removal efficiency. In addition, oxygen volume fraction has a little effect.The highest NO removal efficiency is achieved at the TiO2 content of 0.75 g/L, H2O2 initial concentration of 2.5 mol/L, UV lamp power of 36 W, NO initial content of 206×10-6 and TiO2/H2O2 solution volume of 600 m L. It is beneficial for the development and application of NO removal from coal-fired flue gas with UV/TiO2/H2O2 process.

Enhanced debromination of 4-bromophenol by the UV/sulfite process：Efficiency and mechanism

Halogenated aromatic compounds have attracted increasing concerns due to their toxicity and persistency in the environment, and dehalogenation is one of the promising treatment and detoxification methods. Herein, we systematically studied the debromination efficiency and mechanism of para-bromophenol（4-BP） by a recently developed UV/sulfite process. 4-BP underwent rapid degradation with the kinetics accelerated with the increasing sulfite concentration, pH（6.1–10） and temperature, whereas inhibited by dissolved oxygen and organic solvents. The apparent activation energy was estimated to be 27.8 kJ/mol. The degradation mechanism and pathways of 4-BP were explored by employing N2O and nitrate as the electron scavengers and liquid chromatography/mass spectrometry to identify the intermediates. 4-BP degradation proceeded via at least two pathways including direct photolysis and hydrated electron-induced debromination. The contributions of both pathways were distinguished by quantifying the quantum yields of 4-BP via direct photolysis and hydrated electron production in the system. 4-BP could be readily completely debrominated with all the substituted Br released as Br-, and the degradation pathways were also proposed. This study would shed new light on the efficient dehalogenation of brominated aromatics by using the UV/sulfite process.

DBP formation from degradation of DEET and ibuprofen by UV/chlorine process and subsequent post-chlorination

The formation of disinfection by-products（DBPs） from the degradation of N,N-diethyl-3-methyl benzoyl amide（DEET） and ibuprofen（IBP） by the ultraviolet irradiation（UV）/chlorine process and subsequent post-chlorination was investigated and compared with the UV/H_2O_2 process.The pseudo first-order rate constants of the degradation of DEET and IBP by the UV/chlorine process were 2 and 3.1 times higher than those by the UV/H_2O_2 process, respectively, under the tested conditions. This was due to the significant contributions of both reactive chlorine species U（RCS） and hydroxyl radicals（HO） in the UV/chlorine process. Trichloromethane, 1,1,1-trichloro-2-propanone and dichloroacetic acid were the major known DBPs formed after 90% of both DEET and IBP that were degraded by the UV/chlorine process. Their yields increased by over 50%after subsequent 1-day post-chlorination. The detected DBPs after the degradation of DEET and IBP comprised 13.5% and 19.8% of total organic chlorine（TOCl）, respectively, and the proportions increased to 19.8% and 33.9% after subsequent chlorination, respectively. In comparison to the UV/H_2O_2 process accompanied with post-chlorination, the formation of DBPs and TOCl in the UV/chlorine process together with post-chlorination was 5%–63% higher,Ulikely due to the generation of more DBP precursors from the attack of RCS, in addition to HO.

Effects of UV/Ag-TiO_2/O_3 advanced oxidation on unicellular green alga Dunaliella salina:Implications for removal of invasive species from ballast water

The UV/Ag-TiO2/O3 process was investigated for ballast water treatment using Dunaliella salina as an indicator. Inactivation curves were obtained, and the toxicity of effluent was determined. Compared with individual unit processes using ozone or UV/Ag-TiO2, the inactivation efficiency ofD. salina by the combined UV/Ag-TiO2/O3 process was enhanced. The presence of ozone caused an immediate decrease in chlorophyll a （chl-a） concentration. Inactivation efficiency and chl-a removal efficiency were positively correlated with ozone dose and ultraviolet intensity. The initial total residual oxidant （TRO） concentration of effluent increased with increasing ozone dose, and persistence of TRO resulted in an extended period of toxicity. The results suggest that UV/Ag-TiO2/O3 has potential for ballast water treatment.

Experimental and model comparisons of H_2O_2 assisted UV photodegradation of Microcystin-LR in simulated drinking water

The degradation of Microcystin-LR (MC-LR) in water by hydrogen peroxide assisted ultraviolet (UV/H2O2) process was investigated in this paper. The UV/H2O2 process appeared to be effective in removal of the MC-LR. MC-LR decomposition was primarily ascribed to production of strong and nonselective oxidant-hydroxyl radicals within the system. The intensity of UV radiation, initial concentration of MC-LR, MC-LR purity, dosages of H2O2, the initial solution pH, and anions present in water, to some extent, influenced the degradation rate of MC-LR. A modified pseudo-first-order kinetic model was developed to predict the removal efficiency under different experimental conditions.

Formation of halonitromethanes from methylamine in the presence of bromide during UV/Cl2 disinfection

The UV/Clprocess is commonly used to achieve a multiple-barrier disinfection and maintain residuals. The study chose methylamine as a precursor to study the formation of hightoxic halonitromethanes(HNMs) in the presence of bromide ions(Br-) during UV/Cldisinfection. The maximum yield of HNMs increased first and then decreased with increasing concentration of Br-. An excessively high concentration of Br-induced the maximum yield of HNMs in advance. The maximum bromine incorporation factor(BIF) increased, while the maximum bromine utilization factor(BUF) decreased with the increase of Br-concentration. The maximum yield of HNMs decreased as p H value increased from 6.0 to 8.0 due to the deprotonation process. The BUF value remained relatively higher under an acidic condition, while p H value had no evident influence on the BIF value. The maximum yield of HNMs and value of BUF maximized at a Cl:Br-ratio of 12.5, whereas the BIF value remained relatively higher at low Cl:Br-ratios(2.5 and 5). The amino group in methylamine was first halogenated, and then released into solution as inorganic nitrogen by the rupture of C-N bond or transformed to nitro group by oxidation and elimination pathways. The maximum yield of HNMs in real waters was higher than that in pure water due to the high content of dissolved organic carbon. Two real waters were sampled to verify the law of HNMs formation. This study helps to understand the HNMs formation(especially brominated species) when the UV/Clprocess is adopted as a disinfection technique.

Effect of the ultraviolet/chlorine process on microbial community structure,typical pathogens,and antibiotic resistance genes in reclaimed water

Urban wastewater contains a wide range of pathogens and antibiotic resistance genes(ARGs),which are a serious concern if reusing treated wastewater.However,few studies have explored the microbial communities in reclaimed water using ultraviolet(UV)/chlorine treatment and assessed the changes of the resistome.This study investigated the occurrence of typical pathogens,ARGs,and bacterial communities in UV/chlorine-treated reclaimed water samples.The numbers of culturable and viable but non-culturable pathogens were effectively reduced to 0 CFU/mL within 1–10 and 10–30 min after UV/chlorine treatment,respectively.Meanwhile,the physicochemical indices of water quality were not affected.UV/chlorine treatment could significantly change the bacterial community structure of reclaimed water,showing a decrease in bacterial abundance and diversity.Chlorine-resistant Acinetobacter and Mycobacterium were the dominant bacterial genera(>50%)after UV/chlorine treatment.Moreover,the number of ARGs and mobile genetic elements(MGEs)decreased with an increase in UV/chlorine exposure.However,eight ARGs and three MGEs were consistently detected in more than three seasons,making these major concerns because of their potential role in the persistence and dissemination of antibiotic resistance.Overall,the results of this study suggest that UV/chlorine treatment can potentially improve the microbiological safety of reclaimed water.And more attention should be paid to the pathogens that are both chlorine-resistant and carry MGEs because of their potential for resistance transmission.

Selective elimination of chromophoric and fluorescent dissolved organic matter in a full-scale municipal wastewater treatment plant

Effluent organic matter（Ef OM） from municipal wastewater treatment plants potentially has a detrimental effect on both aquatic organisms and humans.This study evaluated the removal and transformation of chromophoric dissolved organic matter（CDOM） and fluorescent dissolved organic matter（FDOM） in a full-scale wastewater treatment plant under different seasons.The results showed that bio-treatment was found to be more efficient in removing bulk DOM（in term of dissolved organic carbon,DOC） than CDOM and FDOM,which was contrary to the disinfection process.CDOM and FDOM were selectively removed at various stages during the treatment.Typically,the low molecular weight fractions of CDOM and protein-like FDOM were more efficiently removed during bio-treatment process,whereas the humic-like FDOM exhibited comparable decreases in both bio-treatment and disinfection processes.Overall,the performance of the WWTP was weak in terms of CDOM and FDOM removal,resulting in enrichment of CDOM and FDOM in effluent.Moreover,the total removal of the bulk DOM（P 〈 0.05） and the protein-like FDOM（P 〈 0.05） displayed a significant seasonal variation,with higher removal efficiencies in summer,whereas removal of CDOM and the humic-like FDOM showed little differences between summer and winter.In all,the results provide useful information for understanding the fate and transformation of DOM,illustrating that sub-fractions of DOM could be selectively removed depending on treatment processes and seasonality.