Sludge-based activated carbon catalyzed H2O2 oxidation of reactive azo dyes

Heterogeneous electro-Fenton treatment of coking wastewater using Fe/AC/Ni cathode: optimization of electrode and reactor organic loading

A self-developed iron-loaded activated carbon-based nickel foam electrode (Fe/AC/Ni cathode) was used to construct electro-Fenton reaction system to treat coking wastewater. To meet the gap between laboratory beaker experiments and field trials for practical applications, we proposed and validated a method for obtaining organic loads, the essential parameters used in the design of electrochemical systems for wastewater treatment. The three influencing factors most relevant to organic loading, the effective surface area of cathode, chemical oxygen demand (COD) concentration of influent, and treatment time, were selected and investigated for their effects on the COD removal rate of coking wastewater by single-factor experiments and further optimized by response surface method. The appropriate electrode area load (La) and reactor volume load (Lv) were calculated by their corresponding intrinsic relationships with the three factors. The optimum application conditions were effective surface area of cathode 28.5 cm2, COD concentration of influent 1.76 kg·m-3, and treatment time 160.43 min. Under these conditions, the maximum COD removal rate was 98.51%. The La and Lv were 8.905 mgCOD·cm-2·h-1 and 0.634 kgCOD·m-3·h-1, respectively. The characterization experiment results showed that the Fe/AC/Ni cathode had a significant effect on the treatment of refractory organic contaminants in coking wastewater.

Electrochemical degradation of azo dye using granular activated carbon electrodes loaded with bimetallic oxides

The performance of granular activated carbon (GAC) loaded with different combinations of Fe, Co, Ni, Mn, and Ti was examined for the electrochemical degradation of an azo dye such as acid red B (AR-B). Among the bimetallic groups, the combination of Fe and Co exhibited the best degradation effect. X-ray diffraction and X-ray photoelectron spectroscopy revealed that the morphology of the catalyst is CoFe2O4, and scanning electron microscopy manifested that the catalyst is distributed on the GAC surface and holes. The initial pH, hydraulic retention time, and current intensively affected the decolourisation and degradation efficiencies of AR-B, while the electrolyte types and concentrations did not exert any considerable effect. Electron spin resonance spectroscopy indicated that strong signals of hydroxyl radicals are produced by the Fe-Co/GAC electrodes. Results from fluorescence spectroscopy and gas chromatography-mass spectrometry suggested that hydroxyl radicals preferentially attack azo bonds during the degradation of AR-B, forming a series of compounds, and these compounds are finally degraded into small molecules of organic acids, carbon dioxide, and water.

Optimization, kinetics, and thermodynamics aspects in the biodegradation of reactive black 5 (RB5) dye from textile wastewater using isolated bacterial strain, Bacillus albus DD1

This study is aimed to model and optimize the decolorization of reactive black 5 (RB5) dye using Bacillus albus DD1. The response surface methodology (RSM) along with rotatable central composite design (rCCD) is used to optimize the response, % decolorization with four input variables: (i) pH (5-9), initial dye concentration (50-500 ppm), the composition of yeast extract as nitrogen source (0.2-1%) and amount of bacterial inoculum (5-25% v/v). The % decolorization is predicted to be ≈ 98% at the optimized condition (pH = 7.6, dye concentration = 200 ppm, bacterial inoculum = 20 v/v% and yeast extract = 0.4%). Furthermore, the kinetics and thermodynamics of RB5 degradation are also determined. The kinetic order of biodegradation of RB5 is found to follow first-order kinetics with a kinetic rate constant = 0.0384. The activation energy, E_a and frequency factor, A values are calculated as 34.46 kJ/mol and 24,343 (1/Day). A thermodynamic study is also carried out at different temperatures (298 K, 308 K, 310 K, 313 K, and 318 K) using optimized conditions. The values of the ΔH and ΔS are found to be +30.79 kJ/mol, and -0.1 kJ/mol/K, respectively using the Eyring-Polanyi equation. The values of ΔG are also calculated at all temperatures.

Microbial decolorization of Reactive Black 5 dye by Bacillus albus DD1 isolated from textile water effluent: kinetic, thermodynamics & decolorization mechanism

Reactive Black 5 is one of the most widely used dye in textile and other industries. It is one of the significantly toxic azo dye which poses a serious threat to the environment when discharged into water bodies. A bacterial strain having potential to decolourise and degrade RB5 was isolated from textile effluent, and further identified and characterized. On the basis of morphological, biochemical, and 16s rRNA sequence analysis, the isolate was identified as Bacillus albus DD1. It showed 98% removal of RB5 from aqueous medium within 38 h under optimum parameters, pH 7, temperature 40 °C, in the presence of 1% yeast extract as a co-substrate, and 25% inoculum size at the initial dye concentration of 50 mg/l. Kinetic study revealed the decolorization reaction is a first order non- spontaneous reaction. The rate constant and reaction rate for RB5 decolourization in presence of the isolate was 0.0523 s-1 and 2.6 × 10-3 mol/m3 sec, respectively. Values for ΔH and ΔS of the decolourization reaction, determined by thermodynamic analysis, were estimated to be +20.80 kJ/mol and ΔS = -0.1 kJ/mol K, respectively. LC-MS analysis revealed that decolorization was due to degradation of RB5 by cleavage of azo-bond by the bacterium, with the formation of s 3,6,8-trihyroxynapthalene and phthalic acid as degradation products. Therefore, the bacterium Bacillus albus DD1 has potential for application in biological treatment of dye contaminated industrial waste water.

Preparation of sludge-based materials and their environmentally friendly applications in wastewater treatment by heterogeneous oxidation technology

The sludge resource utilization and the high value-added development are environmentally friendly means for sludge treatment. With its rich organic substances and metals content, sludge can replace activated carbon and become a widely used carbon-based material, such as sludge-based activated carbon (SBAC). Meanwhile, as a heterogeneous catalyst, sludge-based catalyst (SBC) can solve the requirements of traditional Fenton catalysts for pH, metal ion leaching, and catalyst recycling. In this paper, combining the properties of SBAC/SBCs, the characteristics of the three methods of activation, support, and hydrothermal preparation of SBAC/SBCs are reviewed. In general, it is necessary to select an appropriate preparation method based on pollutants and environmental treatment goals. Furthermore, compared with other catalysts, SBC heterogeneous oxidation has obvious advantages in refractory organic pollutants. And the reaction mechanism usually involves SO₄·^-, ·OH, O₂·^-, and ¹O₂ processes. Finally, some possible directions for future research involving environmentally friendly SBAC/SBCs are proposed.

Recent Development in Sludge Biochar-Based Catalysts for Advanced Oxidation Processes of Wastewater

Sewage sludge as waste of the wastewater treatment process contains toxic substances, and its conversion into sludge biochar-based catalysts is a promising strategy that merges the merits of waste reutilization and environmental cleanup. This study aims to systematically recapitulate the published articles on the development of sludge biochar-based catalysts in different advanced oxidation processes of wastewater, including sulfate-based system, Fenton-like systems, photocatalysis, and ozonation systems. Due to abundant functional groups, metal phases and unique structures, sludge biochar-based catalysts exhibit excellent catalytic behavior for decontamination in advanced oxidation systems. In particular, the combination of sludge and pollutant dopants manifests a synergistic effect. The catalytic mechanisms of as-prepared catalysts in these systems are also investigated. Furthermore, initial solution pH, catalyst dosage, reaction temperature, and coexisting anions have a vital role in advanced oxidation processes, and these parameters are systematically summarized. In summary, this study could provide relatively comprehensive and up-to-date messages for the application of sludge biochar-based catalysts in the advanced oxidation processes of wastewater treatment.