Fe
O
magnetic nanoparticles (MNPs) are attractive heterogeneous Fenton-like catalysts for oxidative degradation of organic pollutants with H
O
. Herein highly efficient and stable Fe
O
MNPs (Fe
O
...-op-DES, ca. 10nm) were successfully prepared via a novel oxidative precipitation-combined ionothermal synthesis, which comprised oxidative precipitation of FeSO
·7H
O in choline chloride:2urea deep eutectic solvent. Among five different Fe
O
particles tested, Fe
O
-op-DES MNPs exhibited the highest catalytic activity with the activation energy of 47.6kJmol
for degradation of Rhodamine B (RhB) with H
O
under the same conditions (Fe
O
dosage of 0.50gL
, H
O
concentration of 40mmolL
, pH 6.4, 55°C, 2h). Fe
O
-op-DES MNPs were magnetically recoverable, and had good catalytic stability and recyclability without the need of regeneration (>98% degradation efficiency of RhB in 2h and pseudo-first-order rate constant of 0.0376min
after having been continuously running for 12h). The superior catalytic performance of Fe
O
-op-DES MNPs was attributed to the combination of multiple technologically important features, including the nanometer size, high Fe
content, large surface area, high density of surface active sites and stable crystal structure (no phase transformation, negligible iron leaching and particle aggregation after reaction). The wide applicability of Fe
O
-op-DES MNPs was also demonstrated by the degradation of four other organic pollutants.
•Wastewater treatment plants effluents constitute the major source of PhACs in aquatic environment.•Nano-filtration is an effective technique for PhACs removal from wastewater.•Coupling of AOPs with ...membrane filtration as pre/post-treatment or hybrid process.•Hybrid process is only possible with photocatalysis or EAOPs.•EAOPs–membrane filtration is an efficient hybrid wastewater treatment technique.
Pharmaceuticals as emerging pollutants have become a major concern not only because of the threat posed to health and safety of the aquatic life but also due to their continuous accumulation in aquatic environment and development of antibiotic-resistant microbial strains. Single classical water treatment techniques have been generally inadequate for the removal of these hazardous substances. Combined treatment techniques such as membrane separation and advanced oxidation processes (AOPs) is an exciting technology for complete removal of these pollutants because each technique complements the advantages and overcomes the challenges of the other. Technical flexibility of membrane separation technology has allowed possible integration/coupling with several AOPs as: pretreatment stage for removal of organics (which may cause membrane fouling) from membrane feed stream; post-treatment stage for oxidation of organics in both membrane permeate and concentrate streams or one pot/hybrid process for concurrent separation and oxidation of pollutants in the feed stream. AOPs such as ozonation, peroxone (O3/H2O2), UV/H2O2, photo-Fenton, photocatalysis and electrochemical advanced oxidation processes (EAOPs) have been successfully integrated with membrane separation for removal of pharmaceuticals from water and they are critically examined in this review.
Display omitted
•Possible reactive species formed in various AOPs were summarized.•Formation mechanisms and influencing factors of reactive species were analyzed.•Various methods for identifying ...reactive species formed in AOPs were introduced.•Reaction mechanisms of different reactive species with pollutants were discussed.
The formation, identification and reaction mechanism of reactive species in various advanced oxidation processes (AOPs) are crucial for understanding the principles of AOPs and the degradation mechanism of recalcitrant organic contaminants because reactive species are responsible for the degradation of organic contaminants in AOPs. In this review, the possible reactive species generated in various AOPs (such as Fenton oxidation, photochemical oxidation, electrochemical oxidation, ozonation, gamma ray/electron beam radiation, persulfate-based oxidation, wet air oxidation and ultrasonic oxidation), were systematically analyzed and summarized, including hydroxyl radicals (HO), hydrogen radical (H), hydrated electron (eaq−), sulfate radicals (SO4−), peroxymonosulfate radicals (SO5−), superoxide radicals (O2−), singlet oxygen (1O2) and hydroperoxy radicals (HO2). The factors that influence the formation of reactive species were discussed, mainly including pH, inorganic anions and dissolved organic matter. The main identification methods, such as electron spin resonance (ESR), electron paramagnetic electron (EPR), high performance liquid chromatography (HPLC), transient absorption spectrum, quenching experiments and kinetic analysis, were introduced, and the reaction mechanism of reactive species with organic contaminants were discussed. Finally, concluding remarks and perspectives were proposed. This review paper will provide an insight into the formation, identification and reaction mechanism of reactive species in AOPs, which is helpful for reader to better understand the degradation mechanism of recalcitrant organic contaminants in various AOPs.
Display omitted
•Effect of inorganic anions (IA) on the performance of AOPs was summarized.•Effect of IA on the formation and transformation of reactive species was discussed.•Effect of IA on the ...stability of oxidants (H2O2 and persulfate) was evaluated.•Effect of IA on the catalytic activity of catalysts was analyzed.•Inorganic anions have influence on comprehensive performance on AOPs.
Inorganic anions, such as chloridion, carbonate, phosphate, sulfate and nitrate are ubiquitous in water, they will react with hydroxyl radical and sulfate radical produced during advanced oxidation processes (AOPs), to form chlorine radical, carbonate radical nitrate radical, phosphate radical and sulfate radical, which have a significant influence on the transformation of organic pollutants. It is generally believed that the quenching effect of inorganic anions on reactive species produced in AOPs was the main reason to influence the performance of AOPs. While this reason cannot explain all the results. In addition, at present most of studies only focused on the effect of inorganic anions on the removal efficiency of targeted organic pollutant by AOPs. For better understanding the effect of inorganic anions on the performance of AOPs, it is crucial to comprehensively evaluate the effect of inorganic anions on AOPs. In this review paper, the effect of inorganic anions (such as chloridion, carbonate, phosphate, sulfate and nitrate) on the performance of AOPs, including the transformation of reactive species, stability of oxidants, catalytic activity of catalysts and degradation products, was systematically summarized and reviewed. Firstly, their effect on the formation and transformation of reactive species was discussed, then the effect on the stability of oxidants (H2O2 and persulfate) and catalysts was introduced. Furthermore, the effect on the catalytic activity of catalysts was analyzed. Finally, the effect on the degradation intermediate products of organic pollutants was summarized. This review will provide an insight into the underlying influence mechanism of inorganic anions on AOPs, which is conducive to comprehensively evaluate the effect of inorganic anions on the performance of AOPs.
•The traditional mineralization path of CN− was overturned in a novel Electro-Fenton system.•CN− could be converted into NO3− but not CNO− by the synergy of •OH and •O2−.•The Electro-Fenton system ...shows the feasibility of practical application for the actual cyanide residue eluent.
Traditional methods of cyanides’ (CN−) mineralization cannot overcome the contradiction between the high alkalinity required for the inhibition of hydrogen cyanide evolution and the low alkalinity required for the efficient hydrolysis of cyanate (CNO−) intermediates. Thus, in this study, a novel Electro-Fenton system was constructed, in which the free cyanides released from ferricyanide photolysis can be efficiently mineralized by the synergy of •OH and •O2−. The complex bonds in ferricyanide (100 mL, 0.25 mM) were completely broken within 80 min under ultraviolet radiation, releasing free cyanides. Subsequently, in combination with the heterogeneous Electro-Fenton process, •OH and •O2− were simultaneously generated and 92.9% of free cyanides were transformed into NO3- within 120 min. No low-toxic CNO− intermediates were accumulated during the Electro-Fenton process. A new conversion mechanism was proposed that CN− was activated into electron-deficient cyanide radical (•CN) by •OH, and then the •CN intermediates reacted with •O2− via nucleophilic addition to quickly form NO3-, preventing the formation of CNO− and promoting the mineralization of cyanide. Furthermore, this new strategy was used to treat the actual cyanide residue eluent, achieving rapid recovery of irons and efficient mineralization of cyanides. In conclusion, this study proposes a new approach for the mineralization treatment of cyanide-containing wastewater.
Display omitted .
Display omitted
Sulfate radical-based advanced oxidation processes (SR-AOPs) have received intensively attention due to the ability and adaptability. Biochar-based catalysts have been regarded as the ...effective catalysts for activating peroxymonosulfate (PMS) to generate sulfate radicals (SO4•-). This article discussed the advance of the PMS activation by biochar-based catalysts. Firstly, the sources and synthesis methods of biochar-based catalysts have been discussed. Secondly, the different activation mechanisms (including radical pathways and non-radical pathways) of pristine biochar, heteroatom doping biochar and biochar composites catalysts for PMS activation are reviewed, respectively, which includes (i) the significant role of persistent radical (PFRs) and the special structures (defects and graphitization) of pristine biochar, (ii) the effects of element doping (especially N atom) and metal species on the biochar catalysts, (iii) the production mechanisms of reactive oxygen species (ROS) and special non-radical mechanism. Thirdly, the influences of PMS and catalysts concentration, temperature, pH, anions and natural organic matter (NOM) on the contaminants degradation process have been presented. Finally, the conclusion and prospects section discussed the challenges and possible future directions for the degradation of contaminants by biochar/PMS systems. This review is expected to provide new ideas for the application of biochar-based catalysts and broaden the ways for the removal of organic contaminants.
Display omitted
•Unexpected nitration processes led to formation of several nitro-derivatives.•Nitrogen fixation importantly contributes to formation of reactive nitrogen species in ...sonolysis.•Denitration and renitration processes in persulfate based AOPs causes nitration of intermediates.•Post-treatment and nitro-derivatives monitoring are important in AOPs.•Risk of low water quality in case of unexpected nitration during treatment process.
Chemical compounds containing nitro group (nitro-products) are a one of toxic by-products, that can be formed during wastewater treatment processes. In case of presence of nitrite or nitrate ions, the formation of nitro-products during advanced oxidation processes (AOPs) is very common. It is caused by the reactive nitrogen species (RNs) such as nitrate radical (NO3•), nitrite radical (NO2•), nitrogen oxide radical (NO•) and peroxynirite (ONOO–). In fact, the oxidative degradation of N-containing pollutants releases nitrate, nitrite and ammonium ions. In some cases, secondary reactions of mineralised nitrogen species (nitrate and nitrite ions) with the parent or intermediate compound generate next several nitro-products. The nitro-products are more toxic comparing to the primary pollutants and act as the precursors of the nitrogenous disinfection by-products. Moreover, some studies reported unexpected nitro-products formation during the oxidative degradation. In case of such processes a special attention should be made to monitor and minimize these effects. De-nitration of the initial nitro-compounds induces the formation of various nitro-products in AOPs. It was observed for UV light driven, Fenton and persulfate based AOPs. The sonochemical nitrogen fixation is a key mechanism for the formation of nitro-compounds in ultrasounds based AOPs. Therefore, this paper is focused on comparison of various AOPs in terms of nitro-products formation mechanisms and the associated environmental issues.
•Heterogeneous sulfate radical-based advanced oxidation processes were introduced.•Strategies of SFs and SFCs catalyst for PMS activation were overviewed.•Research gaps and needs related to this ...system were proposed.
In recent ten years, the sulfate radical-based advanced oxidation processes (AOPs) have been paid increasing attention due to their superior performance and adaptability in decomposition of organic pollutants. The spinel ferrites (SFs) and spinel ferrite-based composites (SFCs) coupling with peroxymonosulfate (PMS) for heterogeneous catalysis is an efficient way to decompose the organic pollutants by generating reactive sulfate radicals. This article reviewed the recent progress on diverse heterogeneous ferrites (Ni/Cu/Zn/Co/Mn-ferrites) and ferrite composites catalysts (i.e., (Ni/Cu/Zn/Co/Mn-ferrites supported by various substrates) for PMS activation. Besides, impacting factors, synergistic methods of SFs/SFCs-PMS systems in organic decomposition and potential applications were also considered and discussed. Eventually, we proposed the future recommendations and challenges related to SFs and SFCs catalysts, heterogeneous SFs/SFCs-PMS systems and their possible applications in wastewater purification.
Display omitted
•The application of SR-AOPs for IWW treatment was systematically reviewed.•The theoretical (reactive species) and practical aspects (IWW composition) were analyzed.•SR-AOPs are vastly ...studied in landfill leachate and petrochemical IWW effluents.•Its advantages include the simultaneous HO/SO4− generation with non-radical pathways.•Limitations include the difficulty to apply heating, microwave and ultrasound activation.
Over the last years, Sulfate Radical-based Advanced Oxidation Processes (SR-AOPs) have received considerable attention due to their high versatility and efficacy in disinfection and decontamination. Their advantages over classical AOPs, the generation of sulfate radicals (SO4∙-) from peroxydisulfate (PDS, S2O82-), or joint sulfate and hydroxyl radicals (HO∙) production from peroxymonosulfate (PMS, HSO5-) and their abundant activation methods have facilitated their introduction into various remediation and effluent decontamination processes. In this review, we present the advances in the field of industrial wastewater (IWW) treatment by SR-AOPs, by activation of either PMS or PDS via any suitable method, in homogeneous or heterogeneous (photo)catalytic processes. This review aims to present the state of the art in SR-AOPs application for IWW treatment, and act as a guideline of the field advances, summarize the previous application experiences, hence avoid research pitfalls and empower better IWW treatment practices. After an integrated presentation of the dominant pathways towards IWW decontamination, we discuss the SR-AOPs application in the treatment of effluents such as landfill leachate, petrochemical and pharmaceutical WW, pulp or paper industry effluents, textile and winery WW, as well as less studied processes such as coking, olive mill or soil washing effluents. Finally, the advantages and shortcomings of SR-AOPs for IWW treatment, as well as their perspectives are discussed.
Display omitted
•Advanced oxidation processes (AOPs) effectively remove organics from produced water.•Both homogeneous and heterogeneous processes are reviewed and evaluated.•Photo-assisted ...techniques and electrochemistry increase the efficiency of oxidation.•AOPs are flexible in terms of configuration and combination with other treatment steps.•The most effective processes need important development for real-scale implementation.
Produced water is the main by-product generated by fossil fuel extraction activities. This wastewater is often heavily contaminated and associated with significant health, safety, and environmental risks; thus, adequate treatment systems are required to bring these streams to a quality that may be suitable for their recycling, reuse, or discharge into the environment. Advanced oxidation processes (AOPs) are increasingly studied to purify produced waters, and specifically for the removal of organic pollutants in the aqueous and non-aqueous phases. This review evaluates Fenton-based oxidation, heterogeneous catalysis, electro-oxidation, photo-assisted processes, and homogeneous advanced oxidation processes to remove organic contaminants in produced water. The efficiency and applicability of the reviewed approaches are discussed with particular attention to the configurations within the water purification train. Ozonation, Fenton-based techniques, heterogeneous photocatalysis, and anodic oxidation techniques are the most widely researched AOPs in produced water treatment. Photo-assisted processes and electrochemistry have been shown to significantly improve the effectiveness of decontamination of more traditional processes. Oxidation can be exploited as polishing stage of already pre-treated effluents with the final goal of reuse with closing of the water cycle, or as a primary/secondary treatment step to facilitate subsequent biological processes and membrane separation steps. The combination of two oxidation approaches or the oxidation with a membrane-based treatment within the same hybrid system is particularly promising. Challenges, research needs, and future perspectives are thus examined to guide efforts aimed at improving the application of advanced oxidation in produced water treatment and accelerate its implementation at real scale.
PDF