Advanced oxidation process: a sustainable technology for treating refractory organic compounds present in industrial wastewater

A comprehensive review and perspective research in technology integration for the treatment of gaseous volatile organic compounds

Volatile organic compounds (VOCs) are harmful pollutants emitted from industrial processes. They pose a risk to human health and ecosystems, even at low concentrations. Controlling VOCs is crucial for good air quality. This review aims to provide a comprehensive understanding of the various methods used for controlling VOC abatement. The advancement of mono-functional treatment techniques, including recovery such as absorption, adsorption, condensation, and membrane separation, and destruction-based methods such as natural degradation methods, advanced oxidation processes, and reduction methods were discussed. Among these methods, advanced oxidation processes are considered the most effective for removing toxic VOCs, despite some drawbacks such as costly chemicals, rigorous reaction conditions, and the formation of secondary chemicals. Standalone technologies are generally not sufficient and do not perform satisfactorily for the removal of hazardous air pollutants due to the generation of innocuous end products. However, every integration technique complements superiority and overcomes the challenges of standalone technologies. For instance, by using catalytic oxidation, catalytic ozonation, non-thermal plasma, and photocatalysis pretreatments, the amount of bioaerosols released from the bioreactor can be significantly reduced, leading to effective conversion rates for non-polar compounds, and opening new perspectives towards promising techniques with countless benefits. Interestingly, the three-stage processes have shown efficient decomposition performance for polar VOCs, excellent recoverability for nonpolar VOCs, and promising potential applications in atmospheric purification. Furthermore, the review also reports on the evolution of mathematical and artificial neural network modeling for VOC removal performance. The article critically analyzes the synergistic effects and advantages of integration. The authors hope that this article will be helpful in deciding on the appropriate strategy for controlling interested VOCs.

MXene-based composite aerogels with bifunctional ferrous ions for the efficient degradation of phenol from wastewater

Herein, MXene-based composite aerogel (MXene-Fe2+ aerogel) are constructed by a one-step freeze-drying method, using Ti3C2Tx MXene layers as substrate material and ferrous ion (Fe2+) as crosslinking agent. With the aid of the Fe2+ induced Fenton reaction, the synthesized aerogels are used as the particle electrodes to remove phenol from wastewater with three-dimensional electrode technology. Combined with the dual roles of Fe2+ and the highly conductive MXene, the obtained particle electrode possesses extremely effective phenol degradation. The effects of experiment parameters such as Fe2+ to MXene ratio, particle electrode dosage, applied voltage, and initial pH of solution on the removal of phenol are discussed. At pH = 2.5, phenol with 50 mg/L of initial concentration can be completely removed within 50 min at 10 V with the particle electrode dosage of 0.56 g/L. Finally, the mechanism of degradation is explored. This work provides an effective way for phenol degradation by MXene-based aerogel, which has great potential for the degradation of other organic pollutants in wastewater.

Green route to fabrication of Semal-ZnO nanoparticles for efficient solar-driven catalysis of noxious dyes in diverse aquatic environments

This work successfully demonstrates a sustainable and environmentally friendly approach for synthesizing Semal-ZnO nanoparticles (NPs) using the aqueous leaf extract of Bombax ceiba L. These NPs exhibit an absorption peak at approximately 390 nm in the UV-visible spectrum and an energy gap (Eg) of 3.11 eV. Detailed analyses of the morphology and particle size using various spectroscopic and microscopic techniques, XRD, FE-SEM with EDS, and HR-TEM reveal crystallographic peaks attributable to the hexagonal phase, with an average crystal size of 17 nm. The Semal-ZnO NPs also exhibit a notable photocatalytic efficiency for degrading methylene blue (MB) and methyl orange (MO) under sunlight in different water samples collected from diverse natural sources, indicating that they are promising photocatalysts for environmental remediation. The photocatalytic efficiency of the biofabricated Semal-ZnO NPs is impressive, exhibiting a photodegradation rate of up to 99% for MB and 79% for MO in different water samples under exposure to sunlight. The novel phytofabricated Semal-ZnO NPs are thus a beacon of hope for the environment, with their desirable photocatalytic efficiency, pseudo-first-order kinetics, and ability to break down noxious dye pollutants in various aquatic environments.

Simulated sunlight/periodate-triggered formation of toxic halogenated bisphenols in highly saline water

Periodate (PI)-based oxidation using the activators, such as metal ions and light irradiation, has emerged as a feasible treatment strategy for the effective remediation of contaminated water and wastewater. Given the pervasive nature of PI residues and solar exposure during application, the role of solar light in remediating the challenging highly saline water matrices needs to be elucidated. In this study, bisphenol A (BPA) was selected as the targeted micropollutant, which can be efficiently eliminated by the simulated sunlight (SSL)/PI system in the presence of high-level Cl- (up to 846.0 mM) at pH 7.0. The presence of different background constituents of water, such as halides, nitrate, and dissolved organic matter, had no effect, or even accelerated BPA abatement. Particularly, the ubiquitous Br- or I- appreciably enhanced the BPA transformation efficiency, which may be ascribed to the generation of high-selective reactive HOBr or HOI. The in silico predictions suggested that the transformation products generated by halide-mediated SSL/PI systems via halogen substitutions showed greater persistence, bioaccumulation, and aquatic toxicity than BPA itself. These findings highlighted a widespread phenomenon during PI-based oxidative treatment of highly saline water, which needs special attention under solar light illumination.

Decomposition of metal-organic complexes and metal recovery in wastewater: A systematic review and meta-synthesis

Metals are rarely found as free ions in natural and anthropogenic environments, but they are often associated with organic matter and minerals. Under the context of circular economy, metals should be recycled, yet they are difficult to extract for their complex forms in real situations. Based on the protocols of review methodology and the analysis of VOS viewer, there are few reviews on the properties of metal-organic complexes, decomplexation methods, the effect of coexisting ions, the pH influence, and metal recovery methods for the increasingly complicated metal-organic complexes wastewater. Conventional treatment methods such as flocculation, adsorption, biological degradation, and ion exchange fail to decompose metal-organic complexes completely without causing secondary pollution in wastewater. To enhance comprehension of the behavior and morphology exhibited by metal-organic complexes within aqueous solutions, we presented the molecular structure and properties of metal-organic complexes, the decomplexation mechanisms that encompassed both radical and non-radical oxidizing species, including hydroxyl radical (OH), sulfate radical (SO˙4-), superoxide radical (O˙2-), hydrogen peroxide (H2O2), ozone (O3), and singlet oxygen (1O2). More importantly, we reviewed novel aspects that have not been covered by previous reviews considering the impact of operational parameters and coexisting ions. Finally, the potential avenues and challenges were proposed for future research.

The application of ferrous and graphitic N modified graphene-based composite cathode material in the bio-electro-Fenton system driven by sediment microbial fuel cells to degrade methyl orange

In this work, the ferrous (Fe2+) and graphitic N modified graphene-based composite cathode materials (N-rGO/Fe3O4) were developed through an in-situ reduction method, aiming to facilitate the two-electron pathway in the oxidation-reduction process. This approach generated a specific concentration of H2O2, enabling the construction of a sediment bio-electro-Fenton system using Fe2+ released from the cathode materials. Notably, this system operates without the need for proton exchange membranes. During the cathode material preparation, the utilization of Fe2+ as a reduction agent for graphene oxide (GO), triggered ammonia water to form graphitic N in graphene sheets. This addition enhanced the two-electron pathway, resulting in increased H2O2 production. Specifically, when the Fe2+ concentration was maintained at 0.1 mol/L, precise preparation of N-rGO/Fe3O4 occurred, leading to a maximum output voltage of 0.528 V and a maximum power density of 178.17 mW/m2. The degradation of methyl orange (MO) reached 68.91% within a 25-h period, a phenomenon contributed to the presence of graphitic N in the graphene sheets. H2O2, a byproduct of the two-electron pathway in cathode oxidation reduction reaction, played a crucial role in constructing the bio-electro-Fenton system. This system, in conjunction with Fe2+ released from N-rGO/Fe3O4, facilitated the complete degradation process of MO.

Aluminum-based ozone catalysts prepared by mixing method: Characteristics, performance and carbon emissions

Green and low carbon is an essential direction for the development of water treatment technology. Ozone catalysts prepared by the mixing method have advantages in terms of energy consumption and CO2 emissions, but are considered to be insufficient in catalytic efficiency and stability. In this paper, an Mn-Cu-Ce/Al2O3 (MCCA) catalyst was prepared by optimizing the preparation conditions of the mixing method and the types and ratios of active components. Taking petrochemical secondary effluent (PCSE) as the treatment object, the performance of the catalyst and the carbon emission in the preparation process were studied; and compared with the impregnation method. Results showed that compared with catalysts loaded with other components, the MCCA had a higher removal efficiency for TOC (43.04%) and COD (53.18%), which was basically equivalent to the impregnation method, and the treated effluent reached the expected concentration. MCCA promoted the decomposition rate of O3 by ten times, and the main active species generated were found to be •OH and 1O. Similar to the catalytic ozonation by the catalyst prepared by the impregnation method, the adsorption sites and surface hydroxyl groups on the MCCA surface play a significant role in the degradation of pollutants. However, the carbon emission in the catalyst preparation process of the mixing method was 418.68 kg/ton, which was only 44% of the impregnation method (949.67 kg/ton). Under the global low-carbon transition, this study shows that the mixing method aligns more with the concept of green, clean, and efficient ozone catalyst preparation.

Advances in ultrasound-assisted synthesis of photocatalysts and sonophotocatalytic processes: A review

Water pollution and the global energy crisis are two significant challenges that the world is facing today. Ultrasound-assisted synthesis offers a simple, versatile, and green synthetic tool for nanostructured materials that are often unavailable by traditional synthesis. Furthermore, the integration of ultrasound and photocatalysis has recently received considerable interest due to its potential for environmental remediation as a low-cost, efficient, and environmentally friendly technique. The underlying principles and mechanisms of sonophotocatalysis, including enhanced mass transfer, improved catalyst-pollutant interaction, and reactive species production have been discussed. Various organic pollutants as dyes, pharmaceuticals, pesticides, and emerging organic pollutants are targeted based on their improved sonophotocatalytic degradation efficiency. Additionally, the important factors affecting sonophotocatalytic processes and the advantages and challenges associated with these processes are discussed. Overall, this review provides a comprehensive understanding of sono-assisted synthesis and photocatalytic degradation of organic pollutants and prospects for progress in this field.

Magnetic-acoustic actuated spinous microrobot for enhanced degradation of organic pollutants

A growing interest in the development of efficient strategies for the removal of organic pollutants from polluted water is emerging. As such, artificial micro/nano machines performing excellent water purification tasks have recently attracted more research attention of scientists. Hereby a spinous Fe3O4@PPy microrobot is presented that towards an efficient organic pollutant removal by enhancing Fenton-like reaction. The microrobot is fabricated by wrapping polypyrrole (PPy) on a spiny magnetic template prepared from sunflowers pollen. Modulating the sound pressure and frequency of the ultrasonic field enables the Fe3O4@PPy microrobot to present multimode motion, such as violent eruption-like motion caused by local cavitation (ELM), march-like unific motion (MLM), and typhoon-like rotation toward the center gathered motion (TLM). This multimode motion achieves the sufficient locomotion of microrobots in three-dimensional space and effective contact with organic pollutants in polluted water. Furthermore, a 5.2-fold increase in the degradation rate of methylene blue has been realized using Fe3O4@PPy microrobots under low-concentration hydrogen peroxide conditions. Also, the magnetically controlled recovery of microrobots from water after the completion of the degradation task has been demonstrated. The magnetic-acoustic actuated spinous microrobot can be extrapolated to other catalytic microrobot, developing a new strategy for an easier implementation and recovery of microrobot in real applications of water purification.

Microalgal-based bioremediation of emerging contaminants: Mechanisms and challenges

Emerging contaminants (ECs) in different ecosystems have consistently been acknowledged as a global issue due to toxicity, human health implications, and potential role in generating and disseminating antimicrobial resistance. The existing wastewater treatment system is incompetent at eliminating ECs since the effluent water contains significant concentrations of ECs, viz., antibiotics (0.03-13.0 μg L-1), paracetamol (50 μg L-1), and many others in varying concentrations. Microalgae are considered as a prospective and sustainable candidate for mitigating of ECs owing to some peculiar features. In addition, the microalgal-based processes also offer cost and energy-efficient solutions for the bioremediation of ECs than conventional treatment systems. It is pertinent that, microalgal-based processes also provides waste valorization benefits as microalgal biomass obtained after ECs treatment can be potentially applied to generate biofuels. Moreover, microalgae can effectively utilize alternative metabolic (cometabolism) routes for enhanced degradation of ECs. Additionally, the ECs removal via the microalgal biodegradation route is highly promising as it can transform the ECs into less toxic compounds. The present review comprehensively discusses different mechanisms involved in removing ECs and various factors that affect their removal. Also, the technoeconomic feasibility of microalgae than other conventional wastewater treatment methods is summarised. The review also highlighted the different molecular and genetic tools that can augment the activity and robustness of microalgae for better removal of organic contaminants. Finally, we have summarised the challenges and future research required towards microalgal-based bioremediation of emerging contaminants (ECs) as a holistic approach.

Degradation of phenol by perborate in the presence of iron-bearing and carbonaceous materials

We investigated the oxidation of phenol by perborate-a newly proposed oxidant-in the presence of iron-bearing and carbonaceous materials through batch experiments. We hypothesized that the oxidation of phenol by perborate was enhanced due to the formation of reactive oxygen species (ROS) in the presence of iron-bearing or carbonaceous materials. Zero-valent iron and ferrous iron (Fe2+) promoted the oxidation of phenol by perborate. Biochar, granular activated carbon, an anode carbonaceous material recovered from a spent Li-ion battery, and graphite also accelerated the oxidation of phenol by perborate. Quenching experiments with radical scavengers and electron paramagnetic resonance (EPR) analysis revealed that hydroxyl (˙OH) and superoxide (O2˙-) radicals were generated and enhanced the degradation of phenol in the perborate systems. Singlet oxygen (1O2) was involved in the iron-bearing material-perborate systems. Moreover, we found that Persil®, a commercial perborate detergent, enhances the oxidation of phenol in the presence of iron-bearing and carbonaceous materials. Our results suggest that perborate can be used for advanced oxidation processes to remediate recalcitrant organic contaminants in natural environments and engineered systems.

Capability of TiO2 and Fe3O4 nanoparticles loaded onto Algae (Scendesmus sp.) as a novel bio-magnetic photocatalyst to degration of Red195 dye in the sonophotocatalytic treatment process under ultrasonic/UVA irradiation

In this study, the magnetic photocatalyst Scendesmus/Fe3O4/TiO2 was synthesized, and its sonophotocatalytic properties in relation to the degradation of the Red195 dye were evaluated. Particles were characterized using a scanning electron microscope (SEM), Fourier's transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), and a vibrating-sample magnetometer (VSM). At a pH of 5, a photocatalyst dosage of 100 mg, an initial R195 concentration of 100 mg/l, an ultrasound power of 38W, and an exposure time of 20 min, the maximum Red195 removal efficiency (100%) was achieved. After five cycles of recycling, the composite's sonophotocatalytic degradation stability for R195 remains above 95%. Experiments on scavenging indicate that electrons (h+) and hydroxyls (OH-) are indispensable decomposition agents. The removal of R195 by Scendesmus/Fe3O4/TiO2 is consistent with the pseudo-first-order kinetic, Freundlich, and Henderson's isotherm models, as determined by kinetic and isotherm investigations. The negative activation enthalpy of the standard (ΔH°) illuminates the exothermic adsorption mechanism. The increase in standard Gibbs activation free energy (ΔG°) with increasing temperature reveals the process is not spontaneous. As indicated by the negative value of the standard entropy of activation (ΔS°), activation of the reactants resulted in a loss of freedom.

Enhanced Industrial Dye Degradation and Antibacterial Activity Supported by the Molecular Docking Study of Yttrium and Carbon Sphere-Doped Lanthanum Oxide Nanostructures

As the population grows, the scientific community remains focused on researching new materials, methods, and devices to ensure the availability of safe drinking water. The main aim of this research was to decrease the recombination rate of the charge carriers of La2O3 and enhance the catalytic and antimicrobial activity by employing Y/Cs- doped La2O3, respectively. In the current study, different concentrations of yttrium (Y) and a fixed amount of carbon spheres (Cs) doped into lanthanum oxide (La2O3) nanostructures (NSs) were synthesized by the coprecipitation technique. Cs are used as a cocatalyst as they have a high surface area and small size attributed to increased active sites and decreased recombination rate. Moreover, Y was further incorporated as it activates the generation of reactive oxygen species in the inhibition zone, enhancing the antibacterial activity and reducing the emission intensity. Advanced techniques were utilized to determine the structural properties, optical emission and absorption, elemental composition, and d-spacing of the synthesized samples. The reported ternary catalyst works efficiently, improving the catalytic activity and bactericidal potential. Moreover, in silico molecular docking studies, Cs-doped La2O3 and Y/Cs-doped La2O3 nanostructures toward DNA gyrase Escherichia coli showed good efficacy for antibacterial activity.

High-performance NiO@Fe3O4 magnetic core-shell nanocomposite for catalytic ozonation degradation of pharmaceutical pollution

Pharmaceuticals that are present in superficial waters and wastewater are becoming an ecological concern. Therefore, it is necessary to provide high-performance methods to limit the harmful ecological effects of these materials to achieve a sustainable environment. In this research, NiO@Fe3O4 nanocomposite was prepared by the co-precipitation method and utilized in the catalytic ozonation process for the degradation of 1-cyclopropyl-6-fluoro-4-oxo-7-piperazin-1-yl-quinoline-3-carboxylic acid (ciprofloxacin antibiotic), for the first time. The influencing parameters in the degradation process were analyzed and optimized via response surface methodology (RSM). The optimal ciprofloxacin removal efficiency (100%) was found at pH = 6.5, using 7.5 mg of the NiO@Fe3O4 nanocatalyst and 0.2 g L-1 h-1 ozone (O3) flow, applied over 20 min. Results showed a significant synergistic effect in the analyzed system, which makes the proposed catalytic ozonation process more efficient than using the catalyst and ozone separately. Also, based on the kinetic analysis data, the catalytic ozonation process followed the pseudo-first-order model. In addition, the nanocatalyst showed high recyclability and stability (88.37%) after five consecutive catalytic ozonation process cycles. In conclusion, the NiO@Fe3O4 nanocatalyst/O3 system can be effectively used for the treatment of pharmaceutical contaminants.

Hydrodynamic cavitation degradation of hydroquinone using swirl-type micro-nano bubble reactor

This study reports the degradation of hydroquinone using lab-scale hydrodynamic cavitation approach (aswirl-type micro-nano bubble reactor), which is considered a green and effective method. The effects of inlet pressure, gas flow rate, pH and initial hydroquinone concentration on hydroquinone degradation were analysed based on experimental research. After experiments investigation, it was concluded that with pH 7.38, hydroquinone concentration of 50 mg/L, and int pressure of 0.2 MPa, the degradation efficiency of hydroquinone reached 91.25% in wastewater. Furthermore, this study also investigated the degradation effect of hydroquinone wastewater by hydrodynamic cavitation combined with persulfate oxidation (HC + PS). The kinetics of hydroquinone degradation by HC or PS oxidation alone and HC + PS oxidation were also examined. Compared with the degradation method alone, the degradation of hydroquinone by HC + PS was more pronounced, and the enhancement factor was 4.55, which indicates that HC greatly enhances the oxidation capacity of PS. In additon, from viewpoint of energy consumption and operating cost, the synergy of HC + PS (1.05 mM) is also the most promising combination. Based on the detection results of the Gas chromatography-mass spectrometry (GC-MS) the possible degradation pathways of hydroquinone were analysed: under the action of ·OH and the high temperature and pressure by cavitation process, the hydroquinone molecule undergoes dehydrogenation and ring-opening reaction, demethylation and decarboxylation reaction to produce intermediate products, which are finally converted into CO2 and H2O in micro-nano bubble cavitation process.

Chitosan Hydrogels for Water Purification Applications

Chitosan-based hydrogels have gained significant attention for their potential applications in water treatment and purification due to their remarkable properties such as bioavailability, biocompatibility, biodegradability, environmental friendliness, high pollutants adsorption capacity, and water adsorption capacity. This article comprehensively reviews recent advances in chitosan-based hydrogel materials for water purification applications. The synthesis methods, structural properties, and water purification performance of chitosan-based hydrogels are critically analyzed. The incorporation of various nanomaterials into chitosan-based hydrogels, such as nanoparticles, graphene, and metal-organic frameworks, has been explored to enhance their performance. The mechanisms of water purification, including adsorption, filtration, and antimicrobial activity, are also discussed in detail. The potential of chitosan-based hydrogels for the removal of pollutants, such as heavy metals, organic contaminants, and microorganisms, from water sources is highlighted. Moreover, the challenges and future perspectives of chitosan-based hydrogels in water treatment and water purification applications are also illustrated. Overall, this article provides valuable insights into the current state of the art regarding chitosan-based hydrogels for water purification applications and highlights their potential for addressing global water pollution challenges.

Occurrence of per- and polyfluoroalkyl substances in aquatic environments and their removal by advanced oxidation processes

Per- and polyfluoroalkyl substances (PFAS), one of the main categories of emerging contaminants, are a family of fluorinated organic compounds of anthropogenic origin. PFAS can endanger the environment and human health because of their wide application in industries, long-term persistence, unique properties, and bioaccumulation potential. This study sought to explain the accumulation of different PFAS in water bodies. In aquatic environments, PFAS concentrations range extensively from <0.03 (groundwater; Melbourne, Australia) to 51,000 ng/L (Groundwater, Sweden). Additionally, bioaccumulation of PFAS in fish and water biota has been stated to range from 0.2 (Burbot, Lake Vättern, Sweden) to 13,900 ng/g (Bluegill samples, U.S.). Recently, studies have focused on PFAS removal from aqueous solutions; one promising technique is advanced oxidation processes (AOPs), including microwaves, ultrasound, ozonation, photocatalysis, UV, electrochemical oxidation, the Fenton process, and hydrogen peroxide-based and sulfate radical-based systems. The removal efficiency of PFAS ranges from 3% (for MW) to 100% for UV/sulfate radical as a hybrid reactor. Therefore, a hybrid reactor can be used to efficiently degrade and remove PFAS. Developing novel, efficient, cost-effective, and sustainable AOPs for PFAS degradation in water treatment systems is a critical area of research.

Coupling of Fenton reaction and white rot fungi for the degradation of organic pollutants

Advanced oxidation processes (AOPs) are a class of highly efficient pollution remediation technologies that produce oxidising radicals under specific conditions to degrade organic pollutants. The Fenton reaction is a commonly applied AOP. To combine the advantages of AOPs and biodegradation in the remediation of organic pollutants, some studies have developed coupled systems between Fenton AOPs and white rot fungi (WRF) for environmental organic pollutant remediation and have achieved some success. Moreover, a promising system, termed as advanced bio-oxidation processes (ABOPs), mediated by the quinone redox cycling of WRF, has attracted increasing attention in the field. In this ABOP system, the radicals and H₂O₂ produced through the quinone redox cycling of WRF can strengthen Fenton reaction. Meanwhile, in this process, the reduction of Fe³⁺ to Fe²⁺ ensures the maintenance of Fenton reaction, leading to a promising application potential for the remediation of environmental organic pollutants. ABOPs combine the advantages of bioremediation and advanced oxidation remediation. Further understanding the coupling of Fenton reaction and WRF in the degradation of organic pollutants will be of great significance for the remediation of organic pollutants. Therefore, in this study, we reviewed recent remediation techniques for organic pollutants involving the coupled application of WRF and the Fenton reaction, focusing on the application of new ABOPs mediated by WRF, and discussed the reaction mechanism and conditions of ABOPs. Finally, we discussed the application prospects and future research directions of the joint application of WRF and advanced oxidation technologies for the remediation of environmental organic pollutants.

Artificial intelligence-aided preparation of perovskite SrFexZr1-xO3-δ catalysts for ozonation degradation of organic pollutant concentrated water after membrane treatment

Membrane technology has been widely used to treat wastewater from a variety of industries, but it also results in a large amount of concentrated wastewater containing organic pollutants after membrane treatment, which is challenging to decompose. Here in this work, a series of perovskite SrFe_xZr_1-xO_3-δ catalysts were prepared via a modified co-precipitation method and evaluated for catalytic ozone oxidative degradation of m-cresol. An artificial neural intelligence networks (ANN) model was employed to train the experimental data to optimize the preparation parameters of catalysts, with SrFe_0.13Zr_0.87O_3-δ being the optimal catalysts. The resultant catalysts before and after reduction were then thoroughly characterized and tested for m-cresol degradation. It was found that the co-doping of Fe and Zr at the B-site and the improvement of oxygen vacancies and oxygen active species by reduction dramatically increased TOC removal rates up to 5 times compared with ozone alone, with the conversion rate of m-cresol reaching 100%. We also proposed a possible mechanism for m-cresol degradation via investigating the intermediates using GC-MS, and confirmed the good versatility of the reduced SrFe_0.13Zr_0.87O_3-δ catalyst to remove other common organic pollutants in concentrated wastewater. This work demonstrates new prospects for the use of perovskite materials in wastewater treatment.

Sustainable Alternatives for Tertiary Treatment of Pulp and Paper Wastewater

In this work, different alternatives to conventional tertiary treatment of pulp and paper (P&P) wastewater (WW), i.e., physicochemical coagulation-flocculation, were investigated to enhance the environmental and economic sustainability of industrial wastewater treatment. In particular, following a preliminary characterization of secondary effluents, cloth filtration and adsorption were studied, the former by pilot-scale tests, while the latter at laboratory scale. An economic analysis was finally accomplished to verify the full-scale applicability of the most promising technologies. Cloth filtration showed excellent total suspended solids (TSS) removal efficiency (mean 81% removal) but a very limited influence on chemical oxygen demand (COD) (mean 10% removal) due to the prevalence of soluble COD on particulate COD. Adsorption, instead, led to a good COD removal efficiency (50% abatement at powdered activated carbon—PAC—dosage of 400 mg/L). The economic analysis proved that adsorption would be convenient only if a local low-cost (100 €/ton) adsorbent supply chain was established. Ultrafiltration was considered as well as a potential alternative: its huge capital cost (19 M€) could be recovered in a relatively short timeframe (pay-back time of 4.7 years) if the ultrafiltrated effluent could be sold to local industries.