Wastewater Treatment Methods Research Articles

Comparative evaluation between Taguchi method and response surface method for optimization of electrocoagulation process in the context of treatment of dairy industry wastewater.

The presence of a large amount of organic and inorganic pollutants in dairy effluent is a substantial environmental issue. This study investigated electrocoagulation (EC) as a potential treatment method for dairy wastewater under different operating conditions, such as applied voltage (5-25V), electrolysis time (30-90min), and inter-electrode distance (1-2cm) by using aluminum electrodes. This study focuses on achieving the maximum removal of BOD, COD, and nitrate in dairy effluents with the aforementioned operating conditions. The process was optimized using the response surface methodology (RSM) and Taguchi method. RSM method optimized the electrocoagulation operating conditions such as the voltage at 23.75V, time of 90min, and inter-electrode distance at 1.07cm. This optimization achieved the maximum removal percentage of BOD, COD, and nitrate at 79.06%, 84.35%, and 79.64%, respectively, in dairy effluent. Taguchi method optimized the electrocoagulation parameters such as the voltage at 25V, time duration of 90min, and inter-electrode distance of 1.00cm, showcasing improved removal percentages of BOD, COD, and nitrate as 90.54%, 89.28%, and 82.74% respectively. The current study attempts to understand the optimization efficiencies between Taguchi method and response surface method for diary wastewater treatment.

Ferrate as a coagulant prior to sand filters treating secondary wastewater effluent for reuse.

Wastewater reuse is one of the crucial water resources in Egypt due to the ongoing need to increase water resources and close the supply-demand gap. In this study, a new coagulant has been investigated before sand filters as an advanced wastewater treatment method. The sand filter pilot was run at a hydraulic loading rate of 0.75 m/h and two different dosages of three coagulants (Alum, FeCl3, and Ferrate VI) were selected using the jar tests. The sand filter without coagulant removed 12% of BOD5 and 70% of turbidity. Applying in-line coagulation before the sand filter provided effluents with better quality, especially for turbidity, organics, and microorganisms. Ferrate provided the highest removal of turbidity (90%) and BOD5 (93%) at very low dosages and lower costs compared with other coagulants, however, it adversely impacted both conductivity and dissolved solids. A significant effect on reducing bacteria was obtained with 40.0 mg/L of alum. According to the study's findings, the ferrate coagulant enhanced the sand filter's performance producing effluents with high quality, enabling it to meet strict water reuse regulations as well as aquatic environmental and health preservations.

Structural selective regulation of Fe3O4@C composite as adsorbent for removing different organic pollutants

ABSTRACT Many wastewater treatment methods have been developed because large amounts of organic pollutants (OPs) entered into the water bodies and adsorption is one of the classic and important technologies. Recently, magnetic adsorbents have garnered extensive attention due to the high efficiency and distinctive recyclability. The control of their structures and surface properties is crucial. Here, the magnetite@carbon (Fe3O4@C) composite was prepared by coupling microreactor and pyrolysis reactor. The structures and surface properties of the Fe3O4@C were effectively adjusted by changing the pyrolysis temperature and Na2CO3 concentration. The Fe3O4@C composite prepared at 800°C of pyrolysis temperature with 1 mol·L−1 of Na2CO3 concentration has lipophilicity and the highest adsorption capacity of 92# gasoline among those adsorbents, which is as high as 7.6 g·g−1. The Fe3O4@C synthesized at 500°C with 1 mol·L−1 of Na2CO3 concentration has hydrophilicity and the highest adsorption capacity of Rhodamine B and Methyl Blue. The saturated adsorption capacities are about 166 and 301 mg·g−1, respectively. Fe3O4@C can be easily separated from wastewater and simply regenerated with less capacity loss after five cycles. The results show that the Fe3O4@C prepared by this method could be suitable for the removal of different OPs by adjusting the preparation conditions.

Fabrication of hollow electrospun Polypyrrole@Cellulose fibrous membrane for ultrahigh-flux dye removal

Membrane technology is a promising method for wastewater treatment, and the balancing between high water flux and high rejection is crucial but extremely challengeable. Herein, an advanced polypyrrole@cellulose fibrous membrane with a hollow structure was prepared through electrospinning followed by a dip-coating process. The sustainable and low-cost cellulose was applied as the raw material while the nontoxic and environmentally stable polypyrrole was chosen as the active layer. Benefiting from the unique hollow structure and the abundant adsorption sites from the polypyrrole, the resulting membrane achieved 99.4 % rejection of anionic Congo red, along with a water flux of 3025.5 L m−2 h−1, which was 4–140 times higher than that of the previously reported membranes. Moreover, it could also efficiently separate cationic methylene blue (a rejection ratio of >96.0 %). This work confirmed the feasibility of hollow electrospun membrane with high dye rejection at ultrahigh water flux, and offered new possibilities to overcome the conflicts between permeation and selectivity in dyeing wastewater treatment.

Degradation of reactive blue dye under UV irradation using iron based nanocomposites

Abstract The textile industry contributes significantly to environmental pollution through the discharge of non-biodegradable colored dye effluents, emphasizing the need for effective wastewater treatment methods. Traditional approaches, including physical and biological treatments, face limitations, necessitating exploration into advanced oxidation processes (AOPs). Iron-based photocatalysts, particularly those synthesized through green methods, have shown promise in degrading organic pollutants. In this study, iron nanocomposites, including CSINCs, ASINCs, and ACINCs, are synthesized by mixing two different plant extract mixtures with an Iron precursor solution. XRD analysis confirms cubic structures for the prepared nanocomposites, with crystalline sizes of 14.21, 15.79, and 28.74 nm, respectively. UV–vis spectrophotometer shows characteristic absorption peaks in the 380–400 nm range. FESEM imaging reveals spherical particles, and EDX analysis detects typical signals of Fe, O, and C. FTIR spectra indicate various functional groups present in the nanocomposites. The study further focuses on optimizing the degradation of Reactive Blue 171 (RB 171) dye, considering factors such as pH, concentration of RB 171, and photocatalyst concentration. The results demonstrate that ACINCs, specifically at a concentration of 10 mg/100 mL in a mixture with Reactive Blue dye at a concentration of 50 ppm, exhibit enhanced degradation under UV irradiation. This detailed investigation contributes to the understanding of the structural and functional characteristics of Iron nanocomposites and their potential application in the efficient degradation of textile dyes, emphasizing the importance of optimizing key parameters for enhanced photocatalytic performance.

Mechanisms and Strategies of Advanced Oxidation Processes for Membrane Fouling Control in MBRs: Membrane-Foulant Removal versus Mixed-Liquor Improvement.

Membrane bioreactors (MBRs) are well-established and widely utilized technologies with substantial large-scale plants around the world for municipal and industrial wastewater treatment. Despite their widespread adoption, membrane fouling presents a significant impediment to the broader application of MBRs, necessitating ongoing research and development of effective antifouling strategies. As highly promising, efficient, and environmentally friendly chemical methods for water and wastewater treatment, advanced oxidation processes (AOPs) have demonstrated exceptional competence in the degradation of pollutants and inactivation of bacteria in aqueous environments, exhibiting considerable potential in controlling membrane fouling in MBRs through direct membrane foulant removal (MFR) and indirect mixed-liquor improvement (MLI). Recent proliferation of research on AOPs-based antifouling technologies has catalyzed revolutionary advancements in traditional antifouling methods in MBRs, shedding new light on antifouling mechanisms. To keep pace with the rapid evolution of MBRs, there is an urgent need for a comprehensive summary and discussion of the antifouling advances of AOPs in MBRs, particularly with a focus on understanding the realizing pathways of MFR and MLI. In this critical review, we emphasize the superiority and feasibility of implementing AOPs-based antifouling technologies in MBRs. Moreover, we systematically overview antifouling mechanisms and strategies, such as membrane modification and cleaning for MFR, as well as pretreatment and in-situ treatment for MLI, based on specific AOPs including electrochemical oxidation, photocatalysis, Fenton, and ozonation. Furthermore, we provide recommendations for selecting antifouling strategies (MFR or MLI) in MBRs, along with proposed regulatory measures for specific AOPs-based technologies according to the operational conditions and energy consumption of MBRs. Finally, we highlight future research prospects rooted in the existing application challenges of AOPs in MBRs, including low antifouling efficiency, elevated additional costs, production of metal sludge, and potential damage to polymeric membranes. The fundamental insights presented in this review aim to elevate research interest and ignite innovative thinking regarding the design, improvement, and deployment of AOPs-based antifouling approaches in MBRs, thereby advancing the extensive utilization of membrane-separation technology in the field of wastewater treatment.

Season and side-chain length affect the occurrences and behaviors of phthalic acid esters in wastewater treatment plants

Emerging pollutants (EPs) are prevalent in aquatic environments globally. Researchers strive to understand their occurrence and behavior prior to their release into the environment. In this study, we examined five wastewater treatment plants (WWTPs), collected 50 wastewater samples and 10 sludge samples. We explored the sources and destinations of phthalic acid esters (PAEs) within these WWTPs using mass balance equations. Wastewater treatment diminished the frequency and concentration of PAEs, and decreased the fraction of short-chain PAEs. We confirmed the increased concentration of PAEs post-primary treatment and modified the mass balance equation. Calculations suggest that weaker “the mix” in winter than in summer and stronger sedimentation in winter than in summer resulted in high efficiency of PAEs removal by winter wastewater treatment. The mass flux of biodegradation was influenced by the combination of biodegradation efficiency and the strength of the particular type of PAEs collected, with no seasonal differences. Mass fluxes for sludge sedimentation were mainly influenced by season and were higher in winter than in summer. This study enhances our understanding of emerging pollutants in manual treatment facilities and offers insights for optimizing wastewater treatment methods for water professionals.

Magnetically Sensitive Carbon-Based Nanocomposites for the Removal of Dyes and Heavy Metals from Wastewater: A Review

The methods of wastewater treatment from heavy metal ions and dyes are analyzed, and the key advantages of powdered magnetically sensitive carbon nanocomposites as adsorbents are shown. Methods for selecting and preparing raw materials and activators for the synthesis of such nanocomposites are considered, and methods for synthesizing nanocomposites are analyzed. The properties, modeling of adsorption kinetics and isotherms, and efficiency of magnetic carbon nanocomposites for wastewater treatment from dyes and heavy metals are described.

One-dimensional nanostructure arrays with Schottky Junction enhanced charge separation for the photoelectrocatalytic selective removal of Uranium from wastewater

The photoelectrocatalytic reduction of soluble U(VI) to relatively insoluble U(IV) is a promising method for uranium wastewater treatment. However, the strong reliance on sacrificial agents and an inert atmosphere due to the rapid charge reorganization remains a great challenge. The construction of an inner electrical field at a heterojunction interface accompanied by an external electric field provides a promising strategy for enhancing charge transfer. Herein, a photoelectrode was proposed by in-situ coating nano-TiO2 cone arrays (NTCA) on a titanium mesh, and used for uranium removal from complex effluents under air conditions without sacrificial agents. The enhanced spatial charge separation driven by the Schottky junction built-in electric field and an external bias voltage, coupled with rapid fluid diffusion, granted the photoelectrode an outstanding photoelectrocatalytic uranium removal performance with photocurrent densities of up to 3 mA cm−2 at −0.55 VAg/AgCl. The impressive uranium removal performance was maintained in a wide range of chemical conditions, as well as in real seawater and industrial wastewater. Theoretical calculation revealed that uranyl ions were confined on the NTCA surface as [UO2(H2O)5]2+, further reduced to UO2. This work demonstrated a viable route for uranium separation from aqueous solutions with inexhaustible solar energy and minimal electrical energy.

A new ceramic microfiltration membrane based on olive seeds: development and characterization

ABSTRACT The development of low-cost methods for wastewater treatment and the separation of oil-in-water emulsions is of considerable significance. Recently, natural material-based, inexpensive membranes have become a hot area of research. In this work, natural olive seeds were used to develop a novel ceramic membrane support. With the oil filtration process in place, the choice was reached to utilize the olive kernels’ beneficial qualities best. The process involved blending plastic paste with water and organic ingredients, followed by extruding the resulting paste into a porous tubular. After firing at 200 °C/2 h, the membrane's water permeability and porosity were 1,852 L/h m2 bar and 45%, respectively, and its average pore width varied from 2 to 15 μm. The efficiency of the microfiltration membrane in separating oil-in-water emulsions was assessed using two test solutions containing oil concentrations of 500 and 1,000 mg/L. Under a transmembrane pressure of 1 bar, the membrane exhibited exceptional permeate flux exceeding 200 L/m2 h, along with a high oil rejection rate of over 96% across all feed concentrations.

Highly efficient and selective nitrate and Hg(II) removal from wet oxidation flue gas purification wastewater using bifunctional MXene nanofiltration membrane

The wet oxidation process is a promising method for simultaneously removing SO2, NO, and Hg0 from coal-fired flue gas. However, the resource utilization of the resulting wastewater, which is enriched with complex ions such as Hg2+, NH4+, NO3−, and SO42−, remains a significant challenge. To achieve the simultaneous goals of concentrating NH4+/NO3−/SO42− ions, adsorbing and separating Hg2+ ions, and reusing wastewater, a bifunctional MXene composite nanofiltration membrane with large interlayer spacing and excellent electrostatic repulsion was developed. The membrane was prepared by co-depositing MXene nanosheets, carboxylated multi-walled carbon nanotubes (MWCNTs), and sodium dodecyl sulfate (SDS) onto an NF-90 membrane. The resulting MXene-MWCNTs-SDS (MMS-COOH) composite membrane demonstrated exceptional salt rejection of 84.4 % for NO3−, 89.0 % for NH4+, 99.8 % for SO42−, and 99.7 % for Hg2+. After 30 cycles, the membrane structure remained stable, maintaining good reusability, with NH4+ and SO42− rejection still reaching 90.0 %. Moreover, the maximum adsorption capacity for Hg2+ was 2869.6 mg g−1, while the capacities for Cr6+ and Pb2+ were 577.6 and 316.8 mg g−1, respectively. The MMS-COOH composite membrane introduces an innovative method for the benign treatment of wet oxidation flue gas purification wastewater and facilitates the recovery of (NH4)2SO4 and NH4NO3 as fertilizers, holding a promising application prospect.

Bi2O3/MoO3 composites: A synergistic approach towards photocatalytic degradation and enhanced antimicrobial activity

The escalating concerns over the water containments and public health pose the great threat to sustainable environment. In this quest there is strong need of advance materials with sustainable solutions that provides the innovative methods for wastewater treatment. This article explores an in-depth study of synergistic effect of composites for photo degradation of methyl orange (MO) and tetracycline (TC) along with the antimicrobial activity. The composites were synthesized through facile hydrothermal method with the weight concentration of 1%, 3%, 5%, 7% of MoO3 represented by BOMO-1, BOMO-3, BOMO-5 and BOMO-7 respectively. Enhanced photocatalytic reported attributed to efficient charge separation and active sites formation of composites. Moreover significantly improved antibacterial activity of nanostructures occurs because of hetrojunction formation. The synergistic potential of Bi2O3/MoO3 composites resulted the generation of Reactive oxygen species (ROS) which performs the redox reaction to improved their activities. Additionally the fabricated nanomaterials evaluated by different characterization to check their optical, structural, morphological and electronic properties. The dual functionality of Bi2O3/MoO3 makes it a promising material for wastewater treatment as well as environmental remediation. These results predict its widely use for advance catalysis and hydrogen evolution procedure in near future.

Hydroxyl Radical-Based Advanced Oxidation Processes of Red Reactive Dyes by Ultrafine Bubbles Method

The breakdown of dyes, which are environmentally hazardous substances and notoriously difficult to degrade, presents the main treatment challenge for wastewater from textile industries. Most advanced oxidation processes (AOPs) for dye degradation usually use costly decolorizing agents, whose residue from Wastewater Treatment Plants may be hazardous to the environment. The present study aimed to apply ultrafine bubbles (UFBs) for water AOPs to degrade textile dyes. Our most recent innovation, ultrafine bubbles, enables the production of reactive oxygen species recently introduced as oxidants in AOPs. First, the disc diffuser was optimized by introducing various flow rates of 1–5 L Per Minute (LPM) to generate UFBs with unique characteristics observed from Zeta Potential, pH, Dissolved Oxygen (DO), and Oxidation–Reduction Potential (ORP). The air UFBs using a disc diffuser with 3 LPM were selected to degrade the Navacron Ruby S-3B dye solution (1000 Pt-Co). The treatment was optimized on the coagulant dosage (0.25, 0.5, 0.75, and 1 ppm) and bubbling times (0–120 min). As a result, the UFBs were successful in degrading the Navacron Ruby S-3B dye solution, resulting in a 45% reduction in Pt-Co color scale with a bubbling time of only 120 min and minimal coagulant dosage (0.5 ppm) compared to the Navacron Ruby S-3B dye solution treatment commonly using a coagulant dosage of 1.5 ppm without UFBs. Based on FTIR, XRF, and PL analysis, we propose the AOP mechanism of hydroxyl radicals for the Navacron Ruby S-3B dye solution. It is emphasized that UFB water AOPs (UFBs–WAOPs) represent a promising alternative technology for treating textile wastewater without chemicals or decolorizing agents. Thus, the UFBs-WAOPs are economical and environmentally benign textile wastewater treatment methods.

Integration of CeO2 and Bi2O3 nanoparticles with TiO2-x to fabricate QDs-sized visible-light-triggered materials with efficient performances in the photodegradation of contaminants

The design and synthesis of novel materials with significant performance is the main goal for the researcher working on wastewater treatment methods. Hence, in this work, the visible-light-triggered TiO2-x/CeO2/Bi2O3 (denoted as Tov/CeO/BiO) nanocomposites were prepared through a facile hydrothermal route preceded calcination at 400 °C, which presented a QDs size of about 5 nm. The phase, morphology, spectroscopic, textural, and electrochemical characteristics of the samples were investigated by different approaches. The photocatalytic ability was studied against the removal of tetracycline (TC), fuchsine (FS), and malachite green (MG) to exhibit their capability in removing various contaminants. It is confirmed that the Tov/CeO/BiO nanocomposites exhibit higher photocatalytic ability than pure TiO2-x and CeO2/Bi2O3 samples. The degradation rate constants of TC, FS, and MG by Tov/CeO/BiO-4 nanocomposite were 500×10−4, 205×10−4, and 324×10−4 min−1, respectively. The promoted performance is about 16.2, 9.62, and 9.23 folds superior to the TiO2-x, and 38.1, 16.5, and 29.1 times greater than the CeO2/Bi2O3 photocatalyst for the eliminations of TC, FS, and MG pollutants, respectively. The admirable photocatalytic efficiency of the Tov/CeO/BiO nanocomposites was associated with improved light harvesting, effective separation of charge carriers, and improved textural features. Additionally, the quenching tests showed that the holes played a prominent role in the degradation of the target pollutant. The reusability of dual S-scheme Tov/CeO/BiO-4 photocatalyst was studied during four repetitive runs. Ultimately, compared to the untreated solution, it was indicated that the resulting solution after the photocatalytic reaction has a positive impact on the growth of wheat seeds.

Experimental investigation and thermomechanical performance evaluation of supercritical water oxidation of n‐dodecane/tributyl phosphate

AbstractBACKGROUNDNuclear energy has brought immense benefits while also generating a large amount of wastewater that urgently needs to be processed. Supercritical water oxidation (SCWO) technology serves as an efficient method for wastewater treatment. In this study, a SCWO experiment was carried out with organic solvent of 30% tributyl phosphate (TBP) and 70% n‐dodecane. This study investigated the operating parameters and the effects of enhanced oxidation techniques on chemical oxygen demand (COD) removal efficiency. An organic solvent SCWO process was developed, and its energy and exergy efficiencies were assessed using Aspen Plus.RESULTSThe COD removal was about 96.18% at the experimental parameters of 500 °C, 10 min, 25 MPa, oxidation coefficient of 1.5 and material concentration of 4 wt%. COD removal increased by 3.09% with the addition of CeO2. Finally, the overall energy and exergy efficiencies of the SCWO system were found to be 58.8% and 9.1% respectively by Aspen Plus.CONCLUSIONIt was found that the reaction temperature had the greatest effect on the COD removal rate compared with other reaction parameters. The decomposition of organic solvents can be divided into two stages, fast and slow, and the addition of alkali and catalyst can effectively promote the decomposition of waste organic solvents. The experiments showed that SCWO is feasible for the treatment of n‐dodecane/TBP. © 2024 Society of Chemical Industry (SCI).

Microbial Biopolymers: From Production to Environmental Applications—A Review

Industrial evolution and agricultural expansion, explained by continuing population growth, have rendered enormous problems for the world throughout the past few decades, primarily because of waste generation. To reduce environmental impact and dependence on fossil fuels, scientists have explored replacing synthetic polymers with environmentally friendly and sustainable alternatives in many emergent applications. In this regard, microbial biopolymers have gained special attention. Many biopolymers originating from various strains of bacteria, fungi, and algae have been reported and their possible applications have increased rapidly. This review focuses on the wide range of microbial biopolymers, their characteristics, and factors influencing their production. The present study also describes the environmental applications of microbial biopolymers. The use of these biopolymers is very attractive as a value-added and sustainable approach to wastewater treatment. By acting as adsorbents, coagulants, and flocculants as well as filters in membrane processes, microbial biopolymers shine as promising solutions beyond conventional methods. They can be integrated into various stages of the treatment process, further enhancing the efficiency of wastewater treatment methods. Microbial biopolymer applications in bioremediation and soil stabilization are also reviewed. Several studies have demonstrated the strong potential of biopolymers in soil improvement due to their ability to minimize permeability, eliminate heavy metals, stabilize soil, and limit erosion. Challenges related to scaling up and the downstream processing of microbial biopolymers, as well as its future perspectives in environmental applications, are also discussed.

Experimental study on coagulation and adsorption treatment of wastewater in combustion cavity for underground coal gasification

Underground Coal Gasification (UCG) is a promising mineral resource development technology that can transform in-situ coal into combustible gas by controlling combustion. However, wastewater generated during the UCG process can lead to environmental pollution in adjacent areas through diffusion or infiltration. In order to seek an efficient and inexpensive in-situ treatment method for underground gasification combustion zone wastewater, UCG model experiments were conducted to obtain wastewater, and the treatment effects of chemical coagulation and physical adsorption methods were compared in this work. The COD concentration in wastewater from underground combustion zone ranges between 555 ∼ 703 mg/L, with a pH value between 8.26 ∼ 8.85. The organic pollutants mainly come from the dissolution of high carbon components, mainly aromatic compounds in tar, which leads to high toxicity and pollution risk of wastewater. For chemical coagulation method, the removal effect of organic pollutants in combustion zone wastewater by ferric sulfate is better than that of aluminum sulfate due to excellent hydrolysis reaction of Fe3+. The corresponding COD removal rate and COD removal cost are 24.34 % and 0.176 ¥/g, respectively. For physical adsorption method, due to the large total pore volume and wide specific surface area of organic bentonite, it can effectively remove COD content. The COD removal rate and COD removal cost, and COD adsorption capacity are 60.23 %, 0.213 ¥/g, and 89.75 mg/g, respectively. Comprehensive comparison shows that physical adsorption is more suitable for in-situ treatment of combustion zone wastewater.

Implications of the operation of continuous granular activated carbon filters on the effluent quality.

Granular activated carbon (GAC) filtration is a commonly used method for advanced wastewater treatment. Filters can be operated continuously or discontinuously, with continuous operation not requiring feed flow interruption for backwashing and circulation (B/C). This study investigated the influence of B/C on the effluent quality of continuous filters. Two continuous GAC filters were operated for 1.5 years, with analysis of dissolved substances and particulate matter in the influent and effluent. The results indicated that various B/C modes had no impact on the removal of dissolved organic carbon and organic micropollutants (OMP), achieving an OMP removal of over 70% after 5,600 treated bed volumes (m3 treated wastewater per m3 GAC). However, it was evident that continuous B/C over 2-4 h resulted in increased turbidity, total suspended solids over 30 mg/L and total phosphorus concentrations of 1.3 mg/L in the filter effluent. Additionally, the study demonstrated that longer and more intensive B/C processes resulted in GAC size degradation with AC concentrations of up to 6.9 mg/L in the filter effluent, along with a change in GAC particle size. Furthermore, the importance of pre-filtration in reducing particulate matter in the filter influent and decreasing hydraulic head loss could be demonstrated.

Catalytic air oxidation of biogas slurry using Cu sub-nanocluster supported by mesoporous TiZrO4 and protected by SiO2 shell

Biogas slurry, an inevitable outcome of anaerobic digestion (AD), is a treatment burden for urban environmental management. In this study, two kinds of biogas slurry (slurry J and slurry C), collected from the AD plants in Japan and China, were treated using novel TiZrO4 @Cu and TiZrO4 @Cu@SiO2 multilayered hollow spheres containing Cu sub-nanoclusters as the catalyst. The results showed that the chemical oxygen demand (COD) was removed by 63 % for slurry J and 44 % for slurry C after 5 h. The Cu sub-nanoclusters acted as co-catalysts and active centers, facilitating rapid electron transfer to oxygen molecules and forming highly reactive •O2− and •OH species (Use slurry J as the based solution). These free radicals cleaved the interconnecting bonds between benzene rings, disintegrated the ring structure, formed intermediate compounds such as n-hexylic acid, and ultimately mineralized organic pollutants in biogas slurry into CO2 and H2O. At the same time, TiZrO4 @Cu@SiO2 had excellent stability due to the protection of the SiO2 shell and reduced threefold Cu leaching than TiZrO4 @Cu. The COD removal rate was always 60 % in six cycles in the slurry J. The new catalyst ensured the high performance of catalytic air oxidation at low temperatures, which has significant potential as an environmentally friendly and energy-saving method for organic wastewater treatment.

Overview of treatment methods of tannery wastewater

Overview of treatment methods of tannery wastewater