Electro-Fenton degradation of a ternary pharmaceutical mixture and its application in the regeneration of spent biochar

Valorization of nano-scrap carbon iron filings as heterogeneous electro-Fenton catalyst for the removal of anticancer drug: insight into degradation mechanism

This study employs mechanically synthesized nano-scrap carbon iron filings (nSCIF) as a cost-effective and sustainable catalyst in heterogeneous electro-Fenton process. The catalytic behaviour of nSCIF was studied for the oxidation of cytarabine (CBN) under the influence of various experimental parameters such as pH, catalyst dose and applied current density. The highest removal efficiency (~ 99%) was achieved in 90 min of reaction at pH 3, 0.4 g L-1 of nSCIF dose and applied current density of 40 mA cm-2. Being a solid catalyst, nSCIF enhances the production of •OH radicals and promotes the cathodic regeneration of iron species (Fe3+ to Fe2+). The mineralization efficiency reached 78% within 3 h of reaction time. The daughter products generated during the reaction were identified through mass spectrometry analysis where eight major transformation productions were identified. The degradation of CBN was mainly contributed by the oxidation of aromatic ring. These findings corroborate the potential of utilizing industrial waste in the electrocatalytic oxidation of persistent pollutant.

Cutting-edge regeneration technologies for saturated adsorbents: a systematic review on pathways to circular wastewater treatment system

Adsorption seemed like an excellent physicochemical process employed for wastewater treatment. In the last few decades, significant improvements have been made in efficiency and economy to remove contaminants from wastewater using several adsorbents. However, less attention was paid to the regeneration of used adsorbents. Aside from the adsorbent's high adsorption performance, the disposal of spent adsorbents is an environmental concern. Regeneration is an important aspect to stimulate the adsorption efficiency of the spent adsorbent for wastewater treatment. This article reviews the various regeneration techniques like electrochemical regeneration, biological regeneration, thermal regeneration, ultrasound regeneration, and chemical regeneration in detail that have been performed for the renewal of saturated adsorbents. In the ultrasonic regeneration technique, Fe3O4-loaded coffee waste hydrochar adsorbent showed 100% regeneration efficiency (RE) after 1.3 h at the power consumption of 300 W/L. Electrochemical regeneration of granular activated carbon, Nyex, graphene and titanium dioxide composite, and Nyex 1000 showed 100% RE after 3, 0.16, 0.12, and 1.5 h, respectively, with electrolyte Na2SO4 and NaCl. In the regeneration technique, powdered activated carbon showed 90% RE after 48-72 h. Immobilized fungal biomass (Rhizopus nigricans) adsorbent showed 111-115% RE with base (0.01 N NaOH, NaHCO3, and Na2CO3) solvent. The present study addresses issues including waste generation, adsorbent potential and efficiency, eco-friendly techniques, and the release of adsorbed pollutants in regenerating saturated adsorbents. The mechanisms of adsorbent regeneration were thoroughly examined, highlighting the significance of the regeneration process in adsorption. Furthermore, this review discusses the advantages of hybrid regeneration techniques like microwave-activated ultraviolet-advanced oxidation, electro-peroxide approach, electrochemical and electrothermal methods, and the secondary use of spent adsorbents as catalysts, fertilizer, cementitious materials, secondary adsorbent bio-fuels, etc. Using saturated adsorbents is a practical technology for sustainable wastewater treatment that has the potential to minimize pollution and promote a circular economy. This review concludes with a discussion of the present challenges in the regeneration of the used adsorbents, as well as future directions for ensuring the system's feasibility from an economic and environmental standpoint for use on an industrial scale.

Electrode material impact on microbial fuel cell and electro-Fenton systems for enhanced slaughterhouse wastewater treatment: A comparative study of graphite and titanium

The treatment of slaughterhouse wastewater is a complex task demanding careful consideration due to its challenging nature. Therefore, exploring more sustainable treatment methods for this particular type of wastewater is of utmost significance. This research focused on the impact of electrode materials, specifically graphite and titanium, on the efficiency of microbial fuel cells (MFCs) and electro-Fenton systems in treating slaughterhouse wastewater. Both graphite and titanium electrodes displayed increasing current density trends, with titanium outperforming graphite. Titanium showed superior electron transfer and current generation (2.2 to 21.2 mA/m2 ), while graphite ranged from 2.4 to 18.9 mA/m2 . Titanium consistently exhibited higher power density, indicating better efficiency in converting current to power (0.059 to 22.68 mW/m2 ), compared to graphite (0.059 to 12.25 mW/m2 ) over the 48-h period. In removal efficiency within the MFC system alone, titanium exhibited superior performance over graphite in key parameters, including zinc (45.5% vs. 37.19%), total hardness (39.32% vs. 29.4%), and nitrates (66.87% vs. 55.8%). For the electro-Fenton system with a graphite electrode, the removal efficiency ranged from 34.1% to 87.5%, with an average efficiency of approximately 56.2%. This variability underscores fluctuations in the efficacy of the graphite electrode across diverse wastewater treatment scenarios. On the other hand, the electro-Fenton system employing a titanium electrode showed removal efficiency values ranging from 26.53% to 89.99%, with an average efficiency of about 68.4%. The titanium electrode exhibits both a comparatively higher and more consistent removal efficiency across the evaluated scenarios. On the other hand, the integrated system achieved more than 90% removal efficiency from most of the parameters. The study underscores the intricate nature of slaughterhouse wastewater treatment, emphasizing the need for sustainable approaches. PRACTITIONER POINTS: Microbial fuel cell (MFC) and electro-Fenton were investigated for slaughterhouse wastewater treatment. The MFC microbial activity started to decrease after 24 h. The integrated system achieved up to 99.8% removal efficiency (RE) for total coliform bacteria. Up to 99.4% of RE was also achieved for total suspended solids (TSS). The integrated system highly improved RE of the pollutants.

Carbon Gels-Green Graphene Composites as Metal-Free Bifunctional Electro-Fenton Catalysts

The Electro-Fenton (EF) process has emerged as a promising technology for pollutant removal. However, the EF process requires the use of two catalysts: one acting as an electrocatalyst for the reduction of oxygen to H2O2 and another Fenton-type catalyst for the generation of ·OH radicals from H2O2. Thus, the search for materials with bifunctionality for both processes is required for a practical and real application of the EF process. Thus, in this work, bifunctional electrocatalysts were obtained via doping carbon microspheres with Eco-graphene, a form of graphene produced using eco-friendly methods. The incorporation of Eco-graphene offers numerous advantages to the catalysts, including enhanced conductivity, leading to more efficient electron transfer during the Electro-Fenton process. Additionally, the synthesis induced structural defects that serve as active sites, promoting the direct production of hydroxyl radicals via a 3-electron pathway. Furthermore, the spherical morphology of carbon xerogels enhances the accessibility of the reagents to the active sites. This combination of factors results in the effective degradation of Tetracycline (TTC) using metal-free catalysts in the Electro-Fenton process, achieving up to an impressive 83% degradation without requiring any other external or additional catalyst.

Application of Deep Eutectic Solvents (DES) for the Synthesis of Iron Heterogeneous Catalyst: Application to Sulfamethoxazole Degradation by Advanced Oxidation Processes

The development of novel approaches to the remotion of pharmaceuticals in wastewater is a subject of concern due to their effect on living beings and the environment. Advanced oxidation processes and the use of relevant catalysts are feasible treatment alternatives that require further development. The development of suitable heterogeneous catalysts is a necessity. This work proposes the synthesis of an iron catalyst in a deep eutectic solvent (Fe-DES) composed of choline chloride and citric acid, which was physically and chemically characterized using SEM-EDS and TEM, FTIR, RAMAN, XRD and XPS. The characterisation confirmed the presence of iron in the form of hematite. Fe-DES was shown to be a multipurpose catalyst that can be applied in the removal of sulfamethoxazole as a reagent in the Fenton and electro-Fenton processes and as an activator of peroxymonosulfate (PMS) processes. After testing the catalyst with the aforementioned techniques, the best result was achieved by combining these processes in an electro-PMS, with great efficiency achieved by dual activation of the PMS with the catalyst and electric field, attaining total elimination at natural pH in 90 min. Furthermore, the degradation was confirmed by the detection of short-chain carboxylic acids (oxalic, succinic, and acetic) and reduction in toxicity values. These results confirm the suitability of Fe-DES to degrade high-priority pharmaceutical compounds.

One-pot synthesis of graphene hydrogel/M (M: Cu, Co, Ni) nanocomposites as cathodes for electrochemical removal of rifampicin from polluted water

Nowadays, the removal of pharmaceutical contaminants from water resources and wastewater is of great importance due to environmental and health issues. Over the decades, various methods have been reported to remove pollutants from wastewater. Among the developed methods, advanced oxidation processes (AOPs) have received significant attention from researchers. In this study, we report the one-pot synthesis of graphene hydrogel-metal (GH-M, M: Co, Ni, Cu) nanocomposites via the combination of polyol and hydrothermal methods. The structure of the resulting nanocomposites was examined by transmission electron microscopy (TEM), inductively coupled plasma-mass spectroscopy (ICP-MS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Raman spectroscopy methods. Afterward, as-prepared GH-Cu, GH-Co, and GH-Ni nanocomposites were used to prepare cathodes for the electro-Fenton (EF) process to remove rifampicin (RIF) from polluted water. The effect of operational parameters, including current density (mA/cm²), initial pH, initial RIF concentration (mg/L), and process time (min) was investigated via response surface methodology (RSM). The optimal values for current density, pH, initial RIF concentration, and process time using GH-Ni as cathode were 30 mA/cm², 5, 30 mg/L, and 90 min, respectively. The results at optimal values showed that the maximum RIF removal efficiency for GH-Cu, GH-Co, and GH-Ni cathodes was 90.47, 92.60, and 93.69%, respectively. Brunauer Emmett Teller (BET), atomic force microscopy (AFM), energy-dispersive X-ray (EDX), and cyclic voltammetry (CV) analyses were performed to investigate the performance of the cathodes for the RIF removal. Finally, total organic carbon (TOC), gas chromatography-mass spectrometry (GC-MS), and atomic absorption spectroscopy (AAS) analyses were performed for further investigation of the RIF removal from polluted water. The results claimed that one-pot synthesized GH-M cathodes can effectively remove RIF from polluted water through EF process.

Study of the performance of a cylindrical flow-through electro-Fenton reactor using different arrangements of carbon felt electrodes: effect of key operating parameters

In this work, a cylindrical flow-through electro-Fenton reactor containing graphite felt electrodes and an Fe(II) loaded resin was evaluated for the production of the Fenton reaction mixture and for the degradation of amoxicillin (AMX) and fecal coliforms containing aqueous solutions. First, the influence of several factors such as treatment time, current intensity, flow rate, and electrode position was investigated for the electrogeneration of H₂O₂ and the energetic consumption by means of a factorial design methodology using a 2⁴ factorial matrix. Electric current and treatment time were found to be the pivotal parameters influencing the H₂O₂ production with contributions of 40.2 and 26.9%, respectively. The flow rate had low influence on the responses; however, 500 mL min^-1 (with an average residence time of 1.09 min obtained in the residence time distribution analysis) allowed to obtain a better performance due to the high mass transport to and from the electrodes. As expected, polarization was also found to play an important role, since for the cathode-to-anode flow direction, lower H₂O₂ concentrations were observed when compared with the anode-to-cathode flow arrangement, indicating that part of the H₂O₂ produced in the cathode was destroyed at the anode. A fluorescence study of hydroxyl radical production, on the other hand, showed that higher yields were obtained using an anode-to-cathode flow direction (up to 3.88 µM), when compared with experiments carried out using a cathode-to-anode flow path (3.11 µM). The removal of a commercial formulation of the antibiotic AMX was evaluated in terms of total organic carbon, achieving up to 57.9% and 38.63% of pollutant mineralization using synthetic and real sanitary wastewater spiked, respectively. Finally, the efficiency of the process on the inactivation of fecal coliforms in sanitary wastewater samples was assessed, reducing 90% of the bacteria after 5 min of electrolysis.

Limitations and future directions of application of the Fenton-like process in micropollutants degradation in water and wastewater treatment: A critical review

Growing water scarcity and pollution are the main challenges that scientists need to focus on currently. Fenton-like processes are promising for applications related to water and wastewater treatment. Although there have been reviews on the fundamentals and applications of Fenton oxidation, a review focusing on the limitations of Fenton oxidation and their possible solutions is still insufficient. This review summarises the features, advantages, and drawbacks of the classic Fenton process. A comprehensive literature survey was conducted to review studies conducted over the last few decades dealing with the application of Fenton processes to organic pollutant removal from water and wastewater. The present overview highlights the modifications of Fenton processes focusing on industrial applications in water and wastewater treatment, especially for micropollutant degradation. Additionally, this study reviews the possibilities and future directions of research on Fenton-like processes to enable the incorporation of Fenton-based methods into existing water and wastewater treatment technologies, including industrial wastewater. It also presents a novel technological solution and improvements to the Fenton-like process to improve the efficiency and reduce the cost.