p -Arsanilic acid ( p -ASA) is widely used in China as livestock and poultry feed additive for promoting animal growth. The use of organoarsenics poses a potential threat to the environment because it is mostly excreted by animals in its original form and can be transformed by UV–Vis light excitation. This work examined the initial rate and efficiency of p -ASA phototransformation under UV-C disinfection lamp. Several factors influencing p -ASA phototransformation, namely, pH, initial concentration, temperature, as well as the presence of NaCl, NH 4 + , and humic acid , were investigated. Quenching experiments and LC–MS were performed to investigate the mechanism of p -ASA phototransformation. Results show that p -ASA was decomposed to inorganic arsenic (including As(III) and As(V)) and aromatic products by UV-C light through direct photolysis and indirect oxidation. The oxidation efficency of p -ASA by direct photosis was about 32%, and those by HO and 1 O 2 were 19% and 49%, respectively. Cleavage of the arsenic–benzene bond through direct photolysis, HO oxidation or 1 O 2 oxidation results in simultaneous formation of inorganic As(III), As(IV), and As(V). Inorganic As(III) is oxidized to As(IV) and then to As(V) by 1 O 2 or HO . As(IV) can undergo dismutation or simply react with oxygen to produce As(V) as well. Reactions of the organic moieties of p -ASA produce aniline, aminophenol and azobenzene derivatives as main products. The photoconvertible property of p -ASA implies that UV disinfection of wastewaters from poultry and swine farms containing p -ASA poses a potential threat to the ecosystem, especially agricultural environments.
Jing Xu,Xiangyi Shen,Duanli Wang,Chuxuan Zhao,Zizheng Liu,Ivan P. Pozdnyakov,Feng Wu,Jun Xia
The usage of p -arsanilic acid (ASA) in livestock and poultry farms leads to its release into the environment. The phototransformation of ASA generates toxic inorganic arsenic species and organic by-products, which affects the water security of the peripheral river basin. In this work, we have investigated the pH-dependent kinetics and mechanisms of ASA photolysis under Ultraviolet-C (UV-C) light (254 nm) irradiation in the pH range 1–11 in the absence of oxygen. The degradation rate of ASA, the ratio of the generated inorganic arsenic species, and the amount of primary organic by-products were determined under the aforesaid conditions. Our results clearly showed the pH-dependent photochemistry of ASA. The photolysis rate was low under acidic conditions, and As(III) and p -aminophenol were the main products. With increasing pH, the photolysis rate increased significantly, and As(V) and aniline became the main products. A pH-based kinetic model has been established that allows prediction of the generation rates of As(III), As(V), p -aminophenol, and aniline according to the photolysis rate of ASA.
Xiaoxia Ye,Huiting Lin,Ruiyang Chi,Zhixuan Guo,Yuancai Lv,Chunxiang Lin,Yifan Liu,Wei Luo
Efficient and rapid removal of p -arsanilic acid ( p -ASA) in water is very important in environmental protection and human health, however it is still a severe challenge in actual engineering. Herein, a novel sorbent (CF-PEI) was successfully fabricated by simply modifying the amphiphilic skin collagen fiber (CF) substrate with Polyethylenimine (PEI). The as-prepared CF-PEI exhibits high-efficiency adsorption for negatively charged p -ASA with aromatic rings due to the introduction of amino groups and the existence of hydrophobic bands, and the maximum adsorption capacity of CF-PEI for p -ASA was high up to 285.71 mg g −1 . In addition, the adsorption mechanism of CF-PEI on p -ASA mainly includes electrostatic interaction, hydrogen bond and amphiphilicity. The multi-level all-fiber structure of CF makes it mainly focus on surface mass transfer with short mass transfer distance, and its capillary drainage effect can realize large flow and rapid separation. CF-PEI based on CF can realize the ability to separate low-concentration p -ASA with high flow rate and high efficiency. The effective processing volume was 12.5 L g −1 when the separation flux reached as high as 9931.27 L m −2 h −1 . Notably, the p -ASA adsorbed on CF-PEI was almost completely eluted by NaOH (0.5 mol L −1 ). The adsorbent is convenient to prepare, recyclable, high in efficiency, and has a great application prospect in removing organic micro-pollutants.
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