Degradation Of Recalcitrant Pollutants Research Articles

A short-circuited photo-assisted electrochemical cell for wastewater treatment

An economically attractive and highly efficient electrochemical cell is fabricated by connecting a carbon felt (CF) and a steel plate (S). Using this configuration, a photo-stimulated (CF/S) arrangement promotes photo-assisted Fenton reactions that result in the degradation of recalcitrant pollutants in water. As opposed to electro-Fenton reports that describe systems with externally polarized electrodes or photo-Fenton systems that utilize iron modified carbon substrates, this work proposes a short-circuited CF/S arrangement that does not require an external potential source. By following the color removal of a dye solution and the chromatography analysis of an emergent contaminant (sulfamethoxazole (SMX)), it was found that the highest efficiencies for the production of oxidative species are observed for tests performed under O2 saturation and UV light irradiation. Under these conditions, the CF/S arrangement achieves 97 % degradation of SMX (after 60 min) and 40 % of total organic carbon (TOC) removal after 240 min. Interestingly however, the CF/S arrangement also revealed a notable efficiency when anoxic and dark conditions were employed. We postulate that in this case, •OH radicals are produced by means of Fenton-like reactions and in order to support this interpretation, cyclic voltammetry and scanning electronic microscopy (SEM) and X-ray diffraction spectroscopy (XRD) measurements were carried out. The resulting data confirmed a Fenton-like mechanism that was further supported by the detection of •OH radical species that was assessed using coumarin absorption data. This study demonstrates that the CF/S cell is a promising approach for a novel photo-assisted Fenton wastewater treatment.

Performance and degradation pathways of bromuconazole by gamma radiation in aqueous solutions

Gamma irradiation has received increasing attention due to its high potential in the degradation of recalcitrant pollutants. Thus, in the present study, gamma irradiation was used for the degradation of bromuconazole with the presence of hydrogen peroxide (H2O2) as a source of •OH and humic acid as natural organic matter. The effects of initial concentration, irradiation doses and pH were examined. A kinetic study was performed, and the by-products were identified by HPLC-QTOF-MS/MS. Results showed that the degradation process of bromuconazole was pseudo-first-order and 99.9% of bromuconazole was decomposed under an absorbed dose of 1 kGy. The percentage of removal increased with doses and the degradation process was accelerated under neutral conditions. The addition of H2O2 showed a synergistic effect on the decomposition of bromuconazole and the degradation efficiency increased with the increase of H2O2 concentration. Humic acid indicated a negative influence on the degradation efficiency, which decreased from 99.6% to 70.365% at a dose of 0.8 kGy when the humic acid concentration was 20 mg/L. Six degradation products were identified and the kinetic rates of three intermediate compounds were calculated using a Himmelblau-Jones-Bischoff numerical analysis technique. A study conducted by 1H NMR indicated a complete mineralization at 1.2 kGy.

Ultrasound and UV technologies for wastewater treatment using boron-doped diamond anodes

In recent years, electrochemical technologies have found a niche in the degradation of recalcitrant pollutants. In this critical review, some of the most promising electrochemical tools for the removal of aqueous organic pollutants from wastewater are discussed in detail. In particular, we discuss the use of ultrasound and ultraviolet irradiation to enhance electro-oxidation using boron-doped diamond anodes. A brief description of the current state of the most relevant studies, all of which are still at a low technology readiness level, is presented, as applied to synthetic solutions and real effluents in experiments on laboratory and pilot scales.

One-pot synthesis of mesoporous silicas supported Cu single-atom and CuO nanoparticles for peroxymonosulfate-activated degradation of tetracycline over a wide pH range

Peroxymonosulfate activated heterogeneous Fenton-like catalytic reactions are promising in degradation of recalcitrant pollutants. Mesoporous silicas supported high-dispersion Cu species, as a kind of conventional heterogeneous catalysts for extensive applications, are rarely studied for their degradation efficiency in peroxymonosulfate-triggered reactions. In this work, one-pot incorporation method was employed to generate simultaneously Cu single-atom, Cu nanoparticles in mesoporous silicas (like the sample of Cu/Si-3 with 0.68 wt% of Cu) using sodium copper chlorophyllin as Cu source by calcining directly in air atmosphere. Several characterizations confirm the coexistence of Cu single-atom, Cu nanoparticles and mesopore with uniform size distribution. Activated by peroxymonosulfate, Cu/Si-3 was found to be efficient in degradation of tetracycline throughout a wide pH range of 2–11. The radicals of S O 4 g − , ⋅ O H and O 1 2 played their role in the degradation reaction. The underlying catalytic mechanism of the Fenton-like reaction was speculated on the basis of analysis of reactive oxygen species. This work has important implication in reasonable design and fabrication of catalysts with high-dispersion metal and controllable synthesis of functional mesoporous materials, as well as in proper disposal of recalcitrant pollutants including tetracycline. • Composite of Cu single-atom and CuO nanoparticles simultaneously generated by one-pot synthesis under air atmosphere. • Successful preparation of mesoporous materials with uniform size distribution. • Cu single-atom catalysts obtained by calcination without protection of inert gas. • The obtained highly dispersed Cu species favourable in degradation of tetracycline. • The catalyst's wide working pH window of 2–11.

Degradation of ofloxacin by a manganese-oxidizing bacterium Pseudomonas sp. F2 and its biogenic manganese oxides

Fluoroquinolone antibiotics like ofloxacin (OFL) have been frequently detected in the aquatic environment. Recently manganese-oxidizing bacteria (MOB) have attracted research efforts on the degradation of recalcitrant pollutants with the aid of their biogenic manganese oxides (BioMnOx). Herein, the degradation of OFL with a strain of MOB (Pseudomonas sp. F2) was investigated for the first time. It was found that the bacteria can degrade up to 100% of 5 μg/L OFL. BioMnOx and Mn(III) intermediates significantly contributed to the degradation. Moreover, the degradation was clearly declined when the microbial activity was inactivated by heat or ethanol, indicating the importance of bioactivity. Possible transformation products of OFL were identified by HPLC-MS and the degradation pathway was proposed. In addition, the toxicity of OFL was reduced by 66% after the degradation.

Water Depollution and Photo-Detoxification by Means of TiO2: Fluoroquinolone Antibiotics as a Case Study

Photocatalysis by semiconductors is considered one of the most promising advanced oxidation processes (AOPs) and TiO2 is the most well-studied material for the removal of contaminants from the aquatic system. Over the last 20 years, pharmaceuticals have been the most investigated pollutants. They re-enter the environment almost unmodified or slightly metabolized, especially in the aquatic environment, since the traditional urban wastewater treatment plants (WWTPs) are not able to abate them. Due to their continuous input, persistence in the environment, and unpleasant effects even at low concentrations, drugs are considered contaminants of emerging concern (ECs). Among these, we chose fluoroquinolone (FQ) antibiotics as an environmental probe for assessing the role of TiO2 photocatalysis in the degradation of recalcitrant pollutants under environmental conditions and detoxification of surface waters and wastewaters. Due to their widespread diffusion, their presence in the list of the most persistent pollutants, and because they have been deeply investigated and their multiform photochemistry is well-known, they are able to supply rich information, both chemical and toxicological, on all key steps of the oxidative degradation process. The present review article explores, in a non-exhaustive way, the relationship among pollution, toxicity and remediation through titanium dioxide photocatalysis, with particular attention to the toxicological aspect. By using FQs as the probe, in depth indications about the different phases of the process were obtained, and the results reported in this paper may be useful in the improvement of large-scale applications of this technology, and—through generally valid methods—they could be deployed to other pharmaceuticals and emerging recalcitrant contaminants.

Bioremediation: an emerging effective approach towards environment restoration

Environmental pollution and its remediation are one of the major problems around the globe. Broad varieties of pollutants viz. pesticides, hydrocarbons, heavy metals, and dyes, etc. are the key players, which are mainly responsible for environmental pollution. Residual contaminants are also difficult to eliminate. Bioremediation is one of the most efficient technologies for the reduction of environmental pollutants that recovers the contaminated site back to its actual form. So far only a small number of microbes (culturable microbes) have been exploited and a huge microbial diversity is still unexplored. To enhance the metabolic potential of the microbes, ecological restoration and degradation of recalcitrant pollutants, various bioremediation approaches like chemotaxis, biostimulation, bioaugmentation, biofilm formation, application of genetically engineered microorganisms, advanced omics, have been widely used. In the last few years, the metabolic potential of microbes has tremendously improved the realization of degradation and remediation of environmental pollution. Microorganisms help in the restoration of contaminated habitats by cleaning up waste in a environmentally safe manner along with the production of safe end products. This review discusses the important processes involved in enhancing bioremediation and recent advances in microbes and plants associated bioremediation.

Synergistic effects of H2O2 and S2O82− in the gamma radiation induced degradation of congo-red dye: Kinetics and toxicities evaluation

Gamma radiation has received increasing attention due to their high potential in degradation of recalcitrant pollutants. Thus in the present study, gamma radiation was used for degradation of congo-red (CR) dye, a highly toxic and carcinogenic pollutant, in the presence of H2O2 and S2O82−. The CR was significantly degraded by gamma radiation (i.e., 53%), however, presence of H2O2 and S2O82− promoted degradation of CR to 98 and 87%, respectively, at 1184 Gy absorbed dose. The radical scavengers and electron spin resonance studies revealed that gamma radiation decompose H2O2 and S2O82− into OH and SO4− and both OH and SO4− caused degradation of CR. The CR showed high reactivity, i.e., 3.25 × 109 and 8.50 × 108 M−1 s−1 with OH and SO4−, respectively, and removal of CR was inhibited in the presence of OH and SO4− scavengers. The removal of CR was promoted with elevating initial concentrations of H2O2 and S2O82− and decreasing initial concentrations of CR. pH of aqueous solution also significantly influenced removal of the dye. The proposed degradation pathways of CR were established from the OH mediated degradation of CR and nature of identified degradation products. The greater mineralization of CR, formation of small molecular mass degradation product, and decline in concentration of acetate after extended treatment suggest the gamma-ray mediated peroxide based process to be a promising alternative for potential degradation of CR.

Interaction patterns in fluidized-bed Fenton process for the degradation of recalcitrant pollutants: theoretical and experimental insights

The interaction of carriers (SiO2) and Fenton’s reagent during the degradation of recalcitrant pollutant by fluidized-bed Fenton process was investigated. Reactive Black 5 (RB5) was selected as a model pollutant since dyes are recalcitrant to conventional treatment technologies. Quantum chemical simulation and experimental approach were employed to predict the potential interactions among the chemical species involved in the process. Quantum chemical parameters such as highest occupied molecular orbital (HOMO) energy, lowest unoccupied molecular orbital (LUMO) energy, HOMO–LUMO energy gaps were computed and analyzed. Response surface methodology was utilized to investigate the effect of operational parameters and optimize the process performance. The analysis of quantum chemical parameters shows that with a comparatively higher EHOMO of − 8.72 eV, SiO2 can interact with Fe3+ (EHOMO = − 18.74 eV), which explains the crystallization of iron oxide on the carriers. The higher EHOMO–LUMO energy gap value of SiO2 (7.92 eV) indicates its potential interaction with Fe2+, Fe3+ and RB5 due to their lower EHOMO–LUMO energy gaps. RB5 exhibited the lowest hardness value (1.23 eV), indicating that it can be degraded by the hydroxyl radical (2.11 eV). For the experimental part, the process can remove up to 80% and 99.94% of the initial COD and color, respectively, under optimum conditions. The most significant parameters affecting the process performance are [Fe2+] and [Dye]. This study has provided insights into the potential interactions occurring in fluidized-bed Fenton process. The results will be useful toward optimization and scale-up of fluidized-bed Fenton process.

Degradation of PVA (polyvinyl alcohol) in wastewater by advanced oxidation processes

AbstractAdvanced oxidation processes (AOPs) constitute a promising technology to treat wastewater containing organic pollutants that are not easily biodegradable. They have received increasing attention in the research and development of wastewater treatment technologies in recent decades for their removal or degradation of recalcitrant pollutants or as pretreatments to convert pollutants into smaller compounds, which can be treated using conventional biological methods. Polyvinyl alcohol (PVA) is a typical refractory organic pollutant. It has received special attention due to its low biodegradability and the large amount of PVA-containing wastewater discharged from textile and paper mills. This review focuses on PVA removal and PVA wastewater pretreatment by AOPs, which include ozonation, Fenton oxidation, persulfate oxidation, ultrasound cavitation, ionizing radiation, photocatalytic oxidation, wet air oxidation and electrochemical oxidation. The mechanistic degradation pathways of PVA by AOPs are also discussed. In addition, a new classification of AOPs is applied for PVA treatment.

Advanced enzymatic elimination of phenolic contaminants in wastewater: a nano approach at field scale

The removal of recalcitrant chemicals in wastewater treatment systems is an increasingly relevant issue in industrialized countries. The elimination of persistent xenobiotics such as endocrine-disrupting chemicals (EDCs) emitted by municipal and industrial sewage treatment plants remains an unsolved challenge. The existing efficacious physico-chemical methods, such as advanced oxidation processes, are resource-intensive technologies. In this work, we investigated the possibility to remove phenolic EDCs [i.e., bisphenol A (BPA)] by means of a less energy and chemical consuming technology. To that end, cheap and resistant oxidative enzymes, i.e., laccases, were immobilized onto silica nanoparticles. The resulting nanobiocatalyst produced at kilogram scale was demonstrated to possess a broad substrate spectrum regarding the degradation of recalcitrant pollutants. This nanobiocatalyst was applied in a membrane reactor at technical scale for tertiary wastewater treatment. The system efficiently removed BPA and the results of long-term field tests illustrated the potential of fumed silica nanoparticles/laccase composites for advanced biological wastewater treatment.

ChemInform Abstract: Phthalocyanine Metal Complexes: Versatile Catalysts for Selective Oxidation and Bleaching

AbstractReview: 69 refs.

Utilization of phenoxyacetic acid, by strains using either the ortho or meta cleavage of catechol during phenol degradation, after conjugal transfer of tfdA, the gene encoding a 2,4-dichlorophenoxyacetic acid/2-oxoglutarate dioxygenase.

The degradation of recalcitrant pollutants in contaminated soils and waters could be facilitated by broadening the degradative capabilities of indigenous microbes by the conjugal transfer of catabolic genes. The feasibility of establishing bacterial populations that degrade phenoxyacetic acid by conjugal transfer of tfdA, the gene encoding 2,4-dichlorophenoxyacetic acid/2-oxoglutarate dioxygenase, to phenol-degrading strains of Pseudomonas and Ralstonia was examined. The mobilizable plasmid pKJS32 served as a vector for delivery of tfdA and the regulatory gene, tfdS. Transconjugant strains that degraded phenol by an ortho cleavage of catechol grew well on phenoxyacetic acid while those employing a meta cleavage could only grow on phenoxyacetic acid in the presence of benzoic acid or after a prolonged lag period and the appearance of mutants that had gained catechol 1,2-dioxygenase activities. Thus, an ortho cleavage of catechol was essential for degradation of phenoxyacetic acid, suggesting that a product of the ortho-cleavage pathway, probably cis, cis-muconic acid, is an inducer of tfdA gene expression. Establishment of phenoxyacetic-acid-degrading soil populations by conjugal transfer of tfdA would depend on the presence of phenol-degrading recipients employing an ortho cleavage of catechol.

Stability testing of ligninase and Mn‐peroxidase from Phanerochaete chrysosporium

The white-rot fungus Phanerochaete chrysosporium produces extracellular peroxidases (ligninase and Mn-peroxidase) believed to be involved in lignin degradation. These extracellular enzymes have also been implicated in the degradation of recalcitrant pollutants by the organism. Commercial application of ligninase has been proposed both for biomechanical pulping of wood and for wastewater treatment. In vitro stability of lignin degrading enzymes will be an important factor in determining both the economic and technical feasibility of application for industrial uses, and also will be critical in optimizing commercial production of the enzymes. The effects of a number of variables on in vitro stability of ligninase and Mn-peroxidase are presented in this paper. Thermal stability of ligninase was found to improve by increasing pH and by increasing enzyme concentration. For a fixed pH and enzyme concentration, ligninase stability was greatly enhanced in the presence of its substrate veratryl alcohol (3,4-dimethoxybenzyl alcohol). Ligninase also was found to be inactivated by hydrogen peroxide in a second-order process that is proposed to involve the formation of the unreactive peroxidase intermediate Compound III. Mn-peroxidase was less susceptible to inactivation by peroxide, which corresponds to observations by others that Compound III of Mn-peroxidase forms less readily than Compound III of ligninase.