Variation and comparison of biotoxicity during typical biological treatment of dyeing wastewater

In present study, dyeing wastewater samples were collected from three typical dyeing wastewater treatment plants in Wujiang, Shengze and Shanghai, China. Physicochemical properties and biotoxicity indicators (luminescent bacteria acute toxicity and umu genotoxicity) were tested and the relationships among them were analyzed. The results revealed that two biotoxicity indicators varied significantly among different treatment units of three plants. After treatment by plant A, luminescent bacteria acute toxicity of dyeing wastewater reduced effectively, while umu genotoxicity increased significantly. Two biotoxicity indicators exhibited decrease and increase trends during the treatment processes of plant B and plant C, respectively. Correlation analysis indicated that there was little correlation among biotoxicity indicators and physicochemical properties, meanwhile two kinds of biotoxicity indicators were relatively independent. Therefore, it was recommended that comprehensive evaluation of dyeing wastewater toxicity needs the combination of various biotoxicity indicators, and the relationship among biotoxicity indicators and physicochemical properties of dyeing wastewater should be established individually. The results of this study would offer a general understanding and evaluation of biotoxicity during actual dyeing wastewater treatment processes and provide database for toxicity reduction and management of dyeing wastewater.

A novel polyaniline/NiO nanocomposite as a UV and visible-light photocatalyst for complete degradation of the model dyes and the real textile wastewater

The textile processing industry utilizes enormous amounts of water. After the dying process, the wastewater discharged to the environment contains carcinogens, non-biodegradable, toxic, and colored organic materials. This study aimed to develop a nanocomposite material with improved photocatalytic activity to degrade textile dyes and without a need for a post-separation process after the use. For this, nickel oxide nanoparticles (NiO NPs) were synthesized by a simple method in aqueous media. Then, NiO-doped polyaniline (PANI/NiO) with efficient absorption in the visible region (optical band gap of 2.08 eV) synthesized on a stainless steel substrate with electropolymerization of aniline in the aqueous media. The photocatalytic activity of PANI/NiO film was also investigated by the degradation of model dyes. Under UV and visible light irradiation, the PANI/NiO film degraded methylene blue and rhodamine B dyes entirely in 30 min. Moreover, the PANI/NiO film was also utilized to degrade real textile wastewater (RTW) without applying any pre-process; it was entirely decomposed by the nanocomposite film in only 45 min under UV light irradiation. The photocatalytic reaction rate of the pure PANI film is increased as 2.5 and 1.5 times with the addition of NiO NPs under UV and visible light irradiations for degradation RTW, respectively. The photocatalytic efficiency was attributed to reduced electron-hole pair recombination on the photocatalyst surface. Furthermore, the photocatalytic stability is discussed based on re-use experiments. The photocatalytic performance remains nearly unchanged, and the degradation of dyes is kept 94% after five cycles.

Preparation of composite adsorbents of activated carbon supported MgO/MnO2 and adsorption of Rhodamine B

Activated carbon (AC) was modified by MgO and MnO₂ through an impregnation-precipitation-calcination procedure. The batch experiments of adsorption of Rhodamine B (RB) by a modified adsorption material, an MgO-MnO₂-AC composite, were carried out and the characteristics of the composite adsorbent were evaluated. The results showed that manganese/magnesium loading changed the surface area, pore volume and increased the number of active adsorption sites of AC. The highest Brunauer-Emmett-Teller (BET) surface area (1,036.18 m²·g^-1) was obtained for MgO-MnO₂-AC compared with AC. The content of AC loaded with magnesium and manganese was 34.24 and 5.51 mg·g^-1 respectively. The adsorption of RB on MgO-MnO₂-AC was significantly improved. The maximum adsorption capacity of RB on MgO-MnO₂-AC was 16.19 mg·g^-1 at 25 °C under the RB concentration of 50 mg·L^-1. The adsorption of RB by AC and MgO-MnO₂-AC increased with the initial concentration of RB. The adsorption of RB increased first and then decreased when pH was between 3 and 11. The results indicated that the pseudo-second-order kinetic equation and Langmuir equation can be used to describe the adsorption of RB on MgO-MnO₂-AC.

Comparative study of antiestrogenic activity of two dyes after Fenton oxidation and biological degradation

In present study, two methods (Fenton oxidation and biological degradation) were used to degrade azo dye (Reactive Black 5, RB5) and anthraquinone dye (Remazol Brilliant Blue R, RBBR). The changes of antiestrogenic activities of these two dyes through two degradation methods were detected using the yeast two-hybrid assay method. Fluorescence spectroscopy together with gas chromatography-mass spectrometry (GC-MS) method was performed to analyze the metabolites of RB5 and RBBR after Fenton oxidation and biological degradation. Results indicated that by Fenton oxidation, the decolorization of RB5 and RBBR were 99.31% and 96.62%, respectively, which were much higher than that by biological degradation. Dissolved organic carbon (DOC) reduction rates of RB5 and RBBR after Fenton oxidation were also much higher than that after biological degradation. By Fenton oxidation, the antiestrogenic activities of RB5 and RBBR all decreased below detection limit after degradation, while by biological degradation all of them increased significantly after degradation. Fluorescence spectroscopy analysis and GC-MS analysis confirmed the degradation effects of RB5 and RBBR by these two degradation methods. In addition, fluorescence spectroscopy analysis revealed that the metabolites humic acid-like substances might contribute to the increasing of antiestrogenic activity of RB5 and RBBR after biological degradation.

Advanced nitrogen removal from the biological secondary effluent of dyeing wastewater via a biological–ferric–carbon nitrification and denitrification process

The nitrification was easily initiated in Fe–C system; extra carbon source and Fe³⁺ in nitrification liquid were beneficial for denitrification. Good performance of N and COD removal made the technology a good choice for advanced nitrogen removal.