Characterization of ferromagnetic sludge-based activated carbon and its application in catalytic ozonation of p-chlorobenzoic acid

Synthesis of algal-bacterial sludge activated carbon/Fe3O4 nanocomposite and its potential in antibiotic ciprofloxacin removal by simultaneous adsorption and heterogeneous Fenton catalytic degradation

The extensive use of pharmaceuticals has increased their presence in the environment, posing significant ecological and public health concerns. The current study reports the magnetic nanocomposite (M-ABAC) synthesis using the algal-bacterial sludge as the precursor for activated carbon and evaluates its potential in fluoroquinolone antibiotics removal. The activated carbon from algal-bacterial sludge was composited with Fe3O4 nanoparticles using the co-precipitation method. The M-ABAC was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Brunauer-Emmett-Teller (BET) analysis, and vibrating sample magnetometry (VSM). M-ABAC was employed for antibiotic ciprofloxacin (CIP) removal by combined adsorption and heterogenous Fenton degradation. The adsorption studies reveal that the Langmuir isotherm best fits the experimental data, with a maximum adsorption capacity of 81.6 mg/g. Pseudo-second-order kinetic model well describes adsorption kinetics. Fenton catalytic degradation was performed using H2O2 as the activating agent. The optimal H2O2 dosage was observed to be 10 mM. A CIP adsorptive removal efficiency of 75% was observed at 2 g/L dosage of M-ABAC in a 200 ppm CIP solution. Simultaneous adsorption and Fenton catalytic degradation further enhanced the removal efficiency to 92%. Radical scavengers experiment revealed that the hydroxyl radical (•OH) was the dominant reactive oxidation species. The degradation products of the CIP were identified using liquid chromatography quadrupole time-of-flight mass spectroscopy (LC-QTOF-MS). The possible CIP degradation mechanisms include decarboxylation, piperazine moiety degradation, defluorination, and hydroxylation.

Heterogeneous Catalytic Ozonation: Solution pH and Initial Concentration of Pollutants as Two Important Factors for the Removal of Micropollutants from Water

There are several publications on heterogeneous catalytic ozonation; however, their conclusions and the comparisons between them are not always consistent due to the variety of applied experimental conditions and the different solid materials used as catalysts. This review attempts to limit the major influencing factors in order to reach more vigorous conclusions. Particularly, it highlights two specific factors/parameters as the most important for the evaluation and comparison of heterogeneous catalytic ozonation processes, i.e., (1) the pH value of the solution and (2) the initial concentration of the (micro-)pollutants. Based on these, the role of Point of Zero Charge (PZC), which concerns the respective solid materials/catalysts in the decomposition of ozone towards the production of oxidative radicals, is highlighted. The discussed observations indicate that for the pH range 6–8 and when the initial organic pollutants’ concentrations are around 1 mg/L (or even lower, i.e., micropollutant), then heterogeneous catalytic ozonation follows a radical mechanism, whereas the applied solid materials show their highest catalytic activity under their neutral charge. Furthermore, carbons are considered as a rather controversial group of catalysts for this process due to their possible instability under intense ozone oxidizing conditions.

Catalytic Ozonation of Ibuprofen in Aqueous Media over Polyaniline-Derived Nitrogen Containing Carbon Nanostructures

Catalytic ozonation is an important water treatment method among advanced oxidation processes (AOPs). Since the first development, catalytic ozonation has been consistently improved in terms of catalysts used and the optimization of operational parameters. The aim of this work is to compare the catalytic activity of polyaniline (PANI) and thermally treated polyaniline (PANI 900) in the catalytic ozonation of ibuprofen solutions at different pH values (4, 7, and 10). Catalysts were thoroughly characterized through multiple techniques (SEM, Raman spectroscopy, XPS, pHPZC, and so on), while the oxidation process of ibuprofen solutions (100 mgL^-1) was assessed by several analytical methods (HPLC, UV254, TOC, COD, and BOD5). The experimental data demonstrate a significant improvement in ibuprofen removal in the presence of prepared solids (20 min for PANI 900 at pH10) compared with non-catalytic processes (56 min at pH 10). Moreover, the influence of solution pH was emphasized, showing that, in the basic region, the removal rate of organic substrate is higher than in acidic or neutral range. Ozone consumption mgO₃/mg ibuprofen was considerably reduced for catalytic processes (17.55-PANI, 11.18-PANI 900) compared with the absence of catalysts (29.64). Hence, beside the ibuprofen degradation, the catalysts used are very active in the mineralization of organic substrate and/or formation of biodegradable compounds. The best removal rate of target pollutants and oxidation by-products was achieved by PANI 900, although raw polyaniline also presents important activity in the oxidation process. Therefore, it can be stated that polyaniline-based catalysts are effective in the oxidation processes.

Recent Developments in Activated Carbon Catalysts Based on Pore Size Regulation in the Application of Catalytic Ozonation

Due to its highly developed pore structure and large specific surface area, activated carbon is often used as a catalyst or catalyst carrier in catalytic ozonation. Although the pore structure of activated carbon plays a significant role in the treatment of wastewater and the mass transfer of ozone molecules, the effect is complicated and unclear. Because different application scenarios require catalysts with different pore structures, catalysts with appropriate pore structure characteristics should be developed. In this review, we systematically summarized the current adjustment methods for the pore structure of activated carbon, including raw material, carbonization, activation, modification, and loading. Then, based on the brief introduction of the application of activated carbon in catalytic ozonation, the effects of pore structure on catalytic ozonation and mass transfer are reviewed. Furthermore, we proposed that the effect of pore structure is mainly to provide catalytic active sites, promote free radical generation, and reduce mass transfer resistance. Therefore, large external surface area and reasonable pore size distribution are conducive to catalytic ozonation and mass transfer.

Dual Effect of Acetic Acid Efficiently Enhances Sludge-Based Biochar to Recover Uranium From Aqueous Solution

Excess sludge (ES) treatment and that related to the uranium recovery from uranium-containing wastewater (UCW) are two hot topics in the field of environmental engineering. Sludge-based biochar (SBB) prepared from ES was used to recover uranium from UCW. Excellent effects were achieved when SBB was modified by acetic acid. Compared with SBB, acetic acid-modified SBB (ASBB) has shown three characteristics deserving interest: 1) high sorption efficiency, in which the sorption ratio of U(VI) was increased by as high as 35.0%; 2) fast sorption rate, as the equilibrium could be achieved within 5.0 min; 3) satisfied sorption/desorption behavior; as a matter of fact, the sorption rate of U(VI) could still be maintained at 93.0% during the test cycles. In addition, based on the test conditions and various characterization results, it emerged as a dual effect of acetic acid on the surface of SBB, i.e., to increase the porosity and add (−COOH) groups. It was revealed that U(VI) and −COO− combined in the surface aperture of ASBB via single-dentate coordination. Altogether, a new utilization mode for SBB is here proposed, as a means of efficient uranium sorption from UCW.

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.

Performance and mechanism of hydrogen sulfide removal by sludge-based activated carbons prepared by recommended modification methods

The sludge-based activated carbons (SACs) were prepared by sewage sludge and corn straw and modified by ferric nitrate. The H₂S removal performance and the desulfurization mechanism of the modified SAC were studied. Results showed that breakthrough sulfur capacity and saturation sulfur capacity of the SAC prepared by recommended modification were 27.209 mg/g and 48.098 mg/g, which were as 4.68 times and 7.02 times larger as those before modification, respectively. Additionally, results showed that the desulfurization products of unmodified SAC were mainly sulfur, while that of modified SAC were mainly sulfate. These results indicated that ferric nitrate modification changed the way of hydrogen sulfide removal by SAC: the desulfurization process of unmodified SAC can be expressed as S^2- → S⁰ → S⁴⁺ → S⁶⁺, and the oxidative active component was dominated by O*, while that of modified SAC can be expressed as S^2- → S⁰ → S⁶⁺, and the oxidative active components are both Fe³⁺ and O*.

Application of Plasma Treatment in Preparation of Soybean Oil Factory Sludge Catalyst and Its Application in Selective Catalytic Oxidation (SCO) Denitration

At present, the most commonly used denitration process is the selective catalytic reduction (SCR) method. However, in the SCR method, the service life of the catalyst is short, and the industrial operation cost is high. The selective catalytic oxidation absorption (SCO) method can be used in a low temperature environment, which greatly reduces energy consumption and cost. The C/N ratio of the sludge produced in the wastewater treatment process of the soybean oil plant used in this paper is 9.64, while the C/N ratio of the sludge produced by an urban sewage treatment plant is 10⁻20. This study shows that the smaller the C/N ratio, the better the denitration efficiency of the catalyst. Therefore, dried oil sludge is used as a catalyst carrier. The influence of different activation times, and LiOH concentrations, on catalyst activity were investigated in this paper. The denitration performance of catalysts prepared by different activation sequences was compared. The catalyst was characterized by Fourier Transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). The experimental results showed that: (1) When the concentration of the LiOH solution used for activation is 15%, and the activation time is four hours, the denitration effect of the catalyst is the best; (2) the catalyst prepared by activation before plasma roasting has the best catalytic activity.

Surface modification of sludge-derived carbon by phosphoric acid as new electrocatalyst for degradation of acetophenone

Sludge-derived carbons (SCs) were modified by different acids and used as electrocatalyst for electrochemical oxidation degradation of acetophenone. The results showed that SC treated with phosphoric acid (H₃PO₄-SC) exhibited the highest catalytic activity. The degradation efficiency of acetophenone reached 87.0%, and TOC removal was 72.3% under the conditions of 100 mg L^-1 acetophenone, 90 mA cm^-2, and 180 min reaction time. The element content and chemical state of H₃PO₄-SC were measured by XRF, XRD, TGA, FTIR, and Mössbauer spectra, and the results indicated that ferric iron and phosphate on the surface of H₃PO₄-SC might play the main role in acetophenone degradation. The carbonyl-¹³C-labeled acetophenone was first used to investigate the degradation of acetophenone in electrochemical oxidation by NMR.