Activated persulfate by iron-based materials used for refractory organics degradation: a review

Potential of metallurgical iron-containing solid waste-based catalysts as activator of persulfate for organic pollutants degradation

The production of solid wastes in the metallurgical industry has significant implications for land resources and environmental pollution. To address this issue, it is crucial to explore the potential of recycling these solid wastes to reduce land occupation while protecting the environment and promoting resource utilization. Steel slag, red mud, copper slag and steel picking waste liquor are examples of solid wastes generated during the metallurgical process that possess high iron content and Fe species, making them excellent catalysts for persulfate-based advanced oxidation processes (PS-AOPs). This review elucidates the catalytic mechanisms and pathways of Fe2+ and Fe0 in the activation PS. Additionally, it underscores the potential of metallurgical iron-containing solid waste (MISW) as a catalyst for PS activation, offering a viable strategy for its high-value utilization. Lastly, the article provides an outlook towards future challenges and prospects for MISW in PS activation for the degradation of organic pollutants.

Enhancement of norfloxacin degradation by citrate in S-nZVI@Ps system: Chelation and FeS layer

The degradation of organic pollution by sulfur-modified nano zero-valent iron(S-nZVI) combined with advanced oxidation systems has been extensively studied. However, the low utilization of nZVI and low reactive oxygen species (ROS) yield in the system have limited its wide application. Herein, a natural organic acid commonly found in citrus fruits, citric acid (CA), was combined with the conventional S-nZVI@Ps system to enhance the degradation of norfloxacin (NOR). The addition of CA increased the NOR removal by about 31% compared with the conventional S-nZVI@Ps system under the same experimental conditions. Among them, the enhanced effect of CA is mainly reflected in its ability to promote the release of Fe2+ and accelerate the cycling of Fe2+ and Fe3+ to further improve the utilization of nZVI and the generation of ROS; it also promotes the dissolution of the active substance (FeS) on the surface of S-nZVI to further improve the degradation rate of NOR. More importantly, the chelate of CA and Fe2+ (CA-Fe2+) had higher reactivity than alone Fe2+. Free radical quenching and electron spin resonance (ESR) experiments indicated that the main ROS for the degradation of NOR in the CA/S-nZVI@Ps system were SO4•- and OH•. CA-bound sulfur-modifying effects on NOR degradation was systematically investigated, and the degradation mechanism of NOR in CA/S-nZVI@Ps system was explored by various techniques. Additionally, the effect of common anions in water matrix on the degradation of NOR in CA/S-nZVI@Ps system and its degradation of various pollutants were also studied. This study provides a new perspective to enhance the degradation of pollutants by S-nZVI combined with advanced oxidation system, which can help to solve the application boundary problem of S-nZVI.

Chemical and biological combined treatment for sugarcane vinasse: selection of parameters and performance studies

Sugarcane vinasse has been reported as a high strength industrial wastewater that could cause severe environmental pollution due to its complex and bio-refractory compounds. Thus, the combined coagulation and sequencing batch biofilm reactor (SBBR) system was employed for the sugarcane vinasse treatment. This study aims to determine the recommended conditions of various parameters under coagulation and SBBR and investigate the effectiveness of combined processes. First, the approach of the coagulation process could achieve the maximum COD reduction and decolorization efficiencies of 79.0 ± 3.4% and 94.1 ± 1.9%, respectively, under the recommended conditions. Next, SBBR as an integrated biofilm reactor showed excellent synergistic biodegradability, removing 86.6 ± 4.3% COD concentration and 94.6 ± 3.8% color concentration at 3.0 g·COD/L of substrate loading concentration. The kinetic studies of SBBR revealed that the first-order kinetic model was the best fit for COD reduction efficiency. In contrast, the second-order kinetic model was the best fit for decolorization efficiency. The SBBR reaction was further investigated by ultraviolet-visible spectrophotometry (UV-Vis). In the combined processes, SBBR followed by the coagulation process (SBBR-CP) showed greater COD reduction and decolorization efficiencies (97.5 ± 0.3 and 99.4 ± 0.1%) when compared to the coagulation process followed by SBBR (CP-SBBR). This study demonstrated the removal performance and potential application of the combined sequential process to produce effluent that can be reused for bioethanol production and fertigation. This finding provides additional insight for developing effective vinasse treatment using combined chemical and biological processes.

Degradation of refractory organic matter in MBR effluent from treating landfill leachate by the UV-nZVI-H2O2 system

In this study, nano zero-valent iron (nZVI) was used as the Fe²⁺ source in the Fenton reaction, and a UV-nZVI-H₂O₂ system was constructed to efficiently degrade and mineralize refractory organic matter in landfill leachate. The results showed that under the optimal conditions (initial pH = 3, UV = 14 W, nZVI = 0.5 g/L, and [H₂O₂] = 30 mM), the removal efficiencies of total organic carbon, absorbance at 254 nm, and color number were 61.38%, 83.89%, and 85.79%, respectively. Control experiments show that the UV-nZVI-H₂O₂ system has the highest removal rate and mineralization rate of refractory organic matter. The excellent performance of the UV-nZVI-H₂O₂ system is related to a higher H₂O₂ utilization rate. The H₂O₂ residue in the UV-nZVI-H₂O₂ system was the lowest, and the effective utilization rate of H₂O₂ was as high as 98.80%. Alcohol quenching experiments and hydroxyl radical quantitative experiments showed that the dominant reactive oxygen species in the UV-nZVI-H₂O₂ system was HO^• and the yield of HO^• was as high as 2007.80 μM, which was much higher than that in other systems. The results of spectra analysis showed that the low molecular weight, high fluorescence frequency organic matter, and relatively stable aromatic organic matter were significantly degraded after treatment with the UV-nZVI-H₂O₂ system and the aromatic degree, humification degree, molecular weight, and molecular polymerization degree of refractory organic matter were also significantly decreased. The mechanism of the UV-nZVI-H₂O₂ reaction includes homogeneous and heterogeneous Fenton reactions and adsorption and precipitation of organic matter by iron-based colloids. This study can provide theoretical and technical support for the advanced treatment of refractory organic matter in landfill leachate.

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

The world faces tremendous challenges and environmental crises due to the rising strength of wastewater. The conventional technologies fail to achieve the quality water that can be reused after treatment means "zero effluent" discharge of the industrial effluent. Therefore, now the key challenge is to develop improved technologies which will have no contribution to secondary pollution and at the same time more efficient for the socio-economic growth of the environment. Sustainable technologies are needed for wastewater treatment, reducing footprint by recycling, reusing, and recovering resources. Advanced oxidation process (AOP) is one of the sustainable emerging technologies for treating refractory organic contaminants present in different industrial wastewaters like textile, paper and pulp, pharmaceuticals, petrochemicals, and refineries. This critical review emerges details of advanced oxidation processes (AOPs), mentioning all possible permutations and combinations of components like ozone, UV, the catalyst used in the process. Non-conventional AOP systems, microwave, ultrasound, and plasma pulse assisted are the future of the oxidation process. This review aims to enlighten the role of AOPs for the mineralization of refractory organic contaminants (ROC) to readily biodegradable organics that cannot be either possible by conventional treatment. The integrated AOPs can improve the biodegradability of recalcitrant organic compounds and reduce the toxicity of wastewater, making them suitable for further biological treatment.

Disinfection of treated urban effluents for reuse by combination of coagulation/flocculation and Fenton processes

In this study, a combination of coagulation/flocculation and Fenton processes was studied as tertiary treatment in order to generate treated water susceptible to reuse. The combination of both processes has never been applied in disinfection of real urban wastewater. The best removals of turbidity and enterobacteria were achieved when applying a coagulant (FeCl₃) dosage of 120 mg/L and the natural pH of the effluent (7.14). The following Fenton reaction presented the maximal enterobacteria inactivation after 120 min at 25 °C, when using hydrogen peroxide and added iron concentrations of 100 mg/L and 7 mg/L, respectively. The abundance of antibiotic resistant (amoxicillin and sulfamethoxazole) enterobacteria and total enterobacteria, enterococci, and heterotrophs, and antibiotic resistance genes - ARG - (sul1, bla_TEM and qnrS) was evaluated before and after each step of the treatment. Values below 10 CFU/100 mL were achieved for total and resistant cultivable enterobacteria immediately after treatment and after storage for 72 h, therefore meeting the strictest limit imposed for E. coli. Physico-chemical parameters also met the established limits for water reuse. Despite harbouring a rich and diverse bacterial community, the final stored disinfected wastewater contained high relative abundance of potentially hazardous bacteria. Such results point out the need of a deep microbiological characterization of treated wastewater to evaluate the risk of its reuse in irrigation.

Review on the degradation of chlorinated hydrocarbons by persulfate activated with zero-valent iron-based materials

Chlorinated hydrocarbons (CHCs) are often used in industrial processes, and they have been found in groundwater with increasing frequency in recent years. Several typical CHCs, including trichloroethylene (TCE), 1,1,1-trichloroethane (TCA), carbon tetrachloride (CT), etc., have strong cytotoxicity and carcinogenicity, posing a serious threat to human health and ecological environment. Advanced persulfate (PS) oxidation technology based on nano zero-valent iron (nZVI) has become a research hotspot for CHCs degradation in recent years. However, nZVI is easily oxidized to form the surface passivation layer and prone to aggregation in practical application, which significantly reduces the activation efficiency of PS. In order to solve this problem, various nZVI modification solutions have been proposed. This review systematically summarizes four commonly used modification methods of nZVI, and the theoretical mechanisms of PS activated by primitive and modified nZVI. Besides, the influencing factors in the engineering application process are discussed. In addition, the controversial views on which of the two (SO₄·^- and ·OH) is dominant in the nZVI/PS system are summarized. Generally, SO₄·^- predominates in acidic conditions while ·OH prefers neutral and alkaline environments. Finally, challenges and prospects for practical application of CHCs removal by nZVI-based materials activating PS are also analyzed.

Response Surface Methodology for Optimization of Bisphenol A Degradation Using Fe3O4-Activated Persulfate

In this study, the degradation of bisphenol A (BPA) by a magnetite (Fe3O4)/persulfate (PS) system was investigated. The effects of magnetite dosage, PS concentration, BPA concentration, and pH on Fe3O4-activated PS in degrading BPA were investigated using single factor experiments. magnetite dosage, PS concentration, and pH were identified as factors in the response surface experimental protocol. Using Box-Behnken analysis, a quadratic model with a high correlation coefficient (0.9152) was obtained, which was accurate in predicting the experimental results. The optimal parameter conditions obtained by the response surface methodology (RSM) were [magnetite] = 0.3 g/L, [PS] = 0.26 mM, and pH = 4.9, under which the predicted BPA degradation rate was 59.54%, close to the real value.

Enhanced catalytic activity and stability of composite of cellulose film and nano zero-valent iron on Juncus effusus for activating peroxydisulfate to degrade Rhodamine B dye

In this study, a novel peroxydisulfate (PDS) activator (CF-nZVI-JE) was prepared via in-situ loading nano zero-valent iron (nZVI) on Juncus effusus (JE) followed with wrapping a layer of cellulose film (CF). The CF-nZVI-JE had the same 3D structure as the JE, being easy to separate from aqueous solution. The loaded nZVI existed single nanoparticles with a size of 60-100 nm except chain-type agglomeration of nanoparticles due to the stabilization of JE fibers. The activation performance of the CF-nZVI-JE for PDS was evaluated with Rhodamine B (Rh B) as a representative pollutant. Under the optimal activating conditions, the degradation rate of Rh B reached 99% within 30 min in the CF-nZVI-JE/PDS system. After five cycles, the degradation rate of Rh B was still over 85%, suggesting that the CF-nZVI-JE had good reusability. More interestingly, SO₄^·- and ·OH radicals were simultaneously detected in the CF-nZVI-JE/PDS system, but only SO₄^·- existed in the JE-ZVI/PDS system, suggesting the different activation mechanism. Meanwhile, the introduction of CF not only facilitated to the mineralization of Rh B but also significantly reduced the release amount of iron ions. Hence, the CF-nZVI-JE can be employed as a promising PDS activator for the treatment of organic wastewater.

A persulfate oxidation system for removing acid orange from aqueous solution: Evaluation and degradation mechanism

Peroxymonosulfate-based advanced oxidation (PMS-AOP) is a promising technology for the degradation of environmental pollutants. PMS can be activated by various transition metals, especially cobalt-based catalysts, but pure cobalt catalyst suffers from severe metal leakage and poor cyclicality. This study synthesized NiCo₂O₄ using a co-precipitation hydrothermal method. The structures, morphologies, and chemical states of the prepared catalysts were hexagonal sheet structures. The activation of PMS by catalyst (NiCo₂O₄) is investigated in a PMS/carbonate (PC) system for Orange II degradation. The observed pseudo-first-order rate constants (k₁) were assessed by the effects of different water matrices and operation conditions. The results show that k_obs with NiCo₂O₄ were increased by 13 times than that of treatment without NiCo₂O₄. This was mainly due to Co³⁺ and Ni³⁺ act as electron acceptors to capture electrons from the PMS/PC system, forming a good redox cycle with HSO₅^-/SO₅^- and oxidizing Co²⁺/Ni²⁺ to produce a large amount of more active components (e.g., ¹O₂ and SO₄^⋅-). The good reusability and high stability of NiCo₂O₄ were demonstrated by five recycle tests. These results suggest that the NiCo₂O₄/PC system is an efficient and stable method of pollution remediation.

Applications and influencing factors of the biochar-persulfate based advanced oxidation processes for the remediation of groundwater and soil contaminated with organic compounds

Biochar (BC) is a low-cost material rich in carbon, which is being used increasingly as a catalyst in persulfate-based advanced oxidation processes (PS-AOPs) for the remediation of groundwater and soil contaminated with organic compounds. In this work, a general summary of preparation methods and applications of various BC (i.e., pristine BC, magnetic BC, and chemically modified BC) in PS-AOPs is presented. Different influence factors (e.g., pH, anions, natural organic matter) for the degradation of organic compounds are discussed. Meanwhile, the influence of external energy (e.g., solar irradiation, UV-Vis, ultrasonic) is also mentioned. Furthermore, the advantage of different BC in PS-AOPs are compared. Finally, potential problems, challenges, and prospects in the application of biochar-persulfate based advanced oxidation processes (BCPS-AOPs) are discussed in the conclusion and perspective.

Austenitic Stainless Steel as a Catalyst Material for Photo-Fenton Degradation of Organic Dyes

In this paper, a typical austenitic stainless steel was used as a catalyst in the visible photo-Fenton degradation process of two model dyes, methylene blue and methylorange, in the presence of hydrogen peroxide and potassium persulfate as free radical-generating species. The concentration intervals for both peroxide and persulfate were in the range of 333–1667 μg/L. Very high photodecoloration efficiencies have been achieved using peroxide (>93%), while moderate ones have been achieved using persulfate (>75%) at a pH value of 6.5. For methylene blue, the maximum mineralization yield of 74.5% was achieved using 1665 μg/L of hydrogen peroxide, while methylorange was better mineralized using 999 μg/L of persulfate. The photodegradation of the dye occurred in two distinct steps, which were successfully modeled by the Langmuir–Hinshelwood pseudo-first-order kinetic model. Reaction rate constants k between 0.1 and 4.05 h−1 were observed, comparable to those presented in the reference literature at lower pH values and higher concentrations of total iron from the aqueous media.

Iron-based persulfate activation process for environmental decontamination in water and soil

Sulfate radical based advanced oxidation processes have been extensively studied for the degradation of environmental contaminants. Iron-based materials such as ferrous, ferric, ZVI, iron oxides, sulfides etc., and various natural iron minerals have been explored for activating persulfate to generate sulfate radicals. In this review, an overview of different iron activated persulfate systems and their application in the removal of organic pollutants and metals in water and soil are summarised. The chemistry behind the activation of persulfate by homogenous and heterogeneous iron-based materials with/without the assistance of electrochemical techniques are also discussed. Besides, the soil decontamination by iron persulfate system and a brief discussion on the ability of the persulfate system to reduce metals presence in wastewater are also summarised. Finally, future research prospects, believed to be useful for all researchers in this field, based on up to date research progress is also given.