196 research outputs found
Degradation of N-nitrosodimethylamine (NDMA) and its precursor dimethylamine (DMA) in mineral micropores induced by microwave irradiation
No full textRemoval of N-nitrosodimethylamine (NDMA) in drinking water treatment poses a significant technical challenge due to its small molecular size, high polarity and water solubility, and poor biodegradability. Degradation of NDMA and its precursor, dimethylamine (DMA), was investigated by adsorbing them from aqueous solution using porous mineral sorbents, followed by destruction under microwave irradiation. Among the mineral sorbents evaluated, dealuminated ZSM-5 exhibited the highest sorption capacities for NDMA and DMA, which decreased with the density of surface cations present in the micropores. In contrast, the degradation rate of the sorbed NDMA increased with the density of surface cations under microwave irradiation. Evolutions of the degradation products and C/N ratio indicate that the sorbed NDMA and DMA could be eventually mineralized under continuous microwave irradiation. The degradation rate was strongly correlated with the bulk temperature of ZSM-5 and microwave power, which is consistent with the mechanism of pyrolysis caused by formation of micro-scale "hot spots" within the mineral micropores under microwave irradiation. Compared to existing treatment options for NDMA removal, microporous mineral sorption coupled with microwave-induced degradation has the unique advantages of being able to simultaneously remove NDMA and DMA and cause their full mineralization, and thus could serve as a promising alternative method. (C) 2016 Elsevier Ltd. All rights reserved.Natural Science Foundation of China [41472324, 41322024]; National Program for Support of Top-notch Young ProfessionalsSCI(E)[email protected]
Curbing dioxin emissions from municipal solid waste incineration in China: Re-thinking about management policies and practices
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Mechanism, kinetics, and pathways of self-sensitized sunlight photodegradation of phenylarsonic compounds
No full textBeing highly water-soluble, phenylarsonic feed additives discharged in animal wastes can easily accumulate in surface water bodies. The photodegradation mechanism, kinetics, and pathways of p-arsanilic acid (p-ASA), 4-hydrophenylarsonic acid (4-HPAA), and phenylarsonic acid (PAA) in water under simulated and natural sunlight irradiation were investigated. The -AsO(OH)(2) group was cleaved from the aromatic ring during photodegradation, and p-benzoquinone and p-hydroquinone were formed as the major organic degradation intermediates. Experimental results did not indicate any significant direct photolysis of the phenylarsonic compounds under simulated and natural sunlight irradiation, but consistently showed that they sensitized the formation of singlet oxygen, which was responsible for their photodegradation and oxidation of the As(III) released. A simple O-1(2)-based "heterogeneous" model was developed, which could well describe the kinetics of O-1(2) formation and phenylarsonic compound photodegradation under various conditions. Indirect photolysis caused by inorganic ions commonly present in natural waters was negligible, while natural organic matter could significantly inhibit their photodegradation. The half-lives of p-ASA, 4-HPAA, and PM photodegradation under simulated sunlight irradiation (765 W m(-2), 25 degrees C) were 11.82 +/- 0.19, 20.06 +/- 0.10, and 135 +/- 6.0 min, respectively, while their degradation rates under natural sunlight in the Pearl River Delta of southern China were 5 times slower due to lower irradiation intensity and water temperatures (19-23 degrees C). (C) 2016 Elsevier Ltd. All rights reserved.Natural Science Foundation of China [41322024, 41472324, 41202251]; Fundamental Research Funds for the Central Universities [35832015141]; National Program for Support of Top-notch Young ProfessionalsSCI(E)[email protected]
Lead (Pb) isotopic fingerprinting and its applications in lead pollution studies in China: A review
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Municipal solid waste (MSW) as a renewable source of energy: Current and future practices in China
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Sorption of chlorophenols on microporous minerals: mechanism and influence of metal cations, solution pH, and humic acid
No full textSorption of 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) on a range of dealuminated zeolites were investigated to understand the mechanism of their sorption on microporous minerals, while the influence of common metal cations, solution pH, and humic acid was also studied. Sorption of chlorophenols was found to increase with the hydrophobicity of the sorbates and that of the microporous minerals, indicating the important role of hydrophobic interactions, while sorption was also stronger in the micropores of narrower sizes because of greater enhancement of the dispersion interactions. The presence of metal cations could enhance chlorophenol sorption due to the additional electrostatic attraction between metal cations exchanged into the mineral micropores and the chlorophenolates, and this effect was apparent on the mineral sorbent with a high density of surface cations (2.62 sites/nm(2)) in its micropores. Under circum-neutral or acidic conditions, neutral chlorophenol molecules adsorbed into the hydrophobic micropores through displacing the "loosely bound" water molecules, while their sorption was negligible under moderately alkaline conditions due to electrostatic repulsion between the negatively charged zeolite framework and anionic chlorophenolates. The influence of humic acid on sorption of chlorophenols on dealuminated Y zeolites suggests that its molecules did not block the micropores but created a secondary sorption sites by forming a "coating layer" on the external surface of the zeolites. These mechanistic insights could help better understand the interactions of ionizable chlorophenols and metal cations in mineral micropores and guide the selection and design of reusable microporous mineral sorbents for sorptive removal of chlorophenols from aqueous stream.Natural Science Foundation of China [41472324, 41322024]; National Water Pollution Control and Treatment Science and Technology Project [2015ZX07406005-001]; National Program for Support of Topnotch Young ProfessionalsSCI(E)[email protected]
Rapid degradation of p-arsanilic acid with simultaneous arsenic removal from aqueous solution using Fenton process
No full textAlthough banned in some developed countries, p-arsanilic acid (p-ASA) is still used widely as a feed additive for swine production in many countries. With little uptake and transformation in animal bodies, nearly all the p-ASA administered to animals is excreted chemically unchanged in animal wastes, which can subsequently release the more toxic inorganic arsenic species upon degradation in the environment. For safe disposal of the animal wastes laden with p-ASA, we proposed a method of leaching the highly water-soluble p-ASA out of the manure first, followed by treatment of the leachate using the Fenton process to achieve fast oxidation of p-ASA and removal of the inorganic arsenic species released (predominantly arsenate) from solution simultaneously. The effects of solution pH, dosages of H2O2 and Fe2+, and the presence of dissolved organic matter (DOM) on the treatment efficiency were systematically investigated. Under the optimum treatment conditions (0.53 mmol L-1 Fe2+, 2.12 mmol L-1 H2O2, and initial pH of 3.0), p-ASA (10 mg-As L-1) could be completely oxidized to As(V) within 30 min in pure water and 4 natural water samples, and at the final pH of 4.0, the residual arsenic levels in solution phase were as low as 1.1 and 20.1-43.4 mu g L-1 in the two types of water matrixes, respectively. The presence of humic acid significantly retarded the oxidation of p-ASA by scavenging HO center dot, and inhibited the As(V) removal through competitive adsorption on ferric hydroxide. Due to the high contents of DOM in the swine manure leachate samples (TOC at similar to 500 mg L-1), much higher dosages of Fez} (10.0 mmol L-1) and H202 (40.0 mmol L-1) and a longer treatment time (120 min) were required to achieve near complete oxidation of p-ASA (98.0%), while maintaining the levels of residual arsenic in the solution at <70.0 mu g L-1. The degradation pathway of p-ASA in the Fenton process was proposed based on the major degradation products detected. Together, the results demonstrate that the Fenton process is promising as an efficient, robust, and low-cost treatment method for controlling the risk of p-ASA in the animal wastes generated at factory farms. (C) 2015 Elsevier Ltd. All rights reserved.Natural Science Foundation of China [41322024, 41202251, 41472324]; National Program for Support of Top-notch Young ProfessionalsSCI(E)[email protected]
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