Phenol Degradation Pathway Research Articles

Phenol Degradation by Pseudarthrobacter phenanthrenivorans Sphe3

Phenol poses a threat as one of the most important industrial environmental pollutants that must be removed before disposal. Biodegradation is a cost-effective and environmentally friendly approach for phenol removal. This work aimed at studying phenol degradation by Pseudarthrobacter phenanthrenivorans Sphe3 cells and also, investigating the pathway used by the bacterium for phenol catabolism. Moreover, alginate-immobilized Sphe3 cells were studied in terms of phenol degradation efficiency compared to free cells. Sphe3 was found to be capable of growing in the presence of phenol as the sole source of carbon and energy, at concentrations up to 1500 mg/L. According to qPCR findings, both pathways of ortho- and meta-cleavage of catechol are active, however, enzymatic assays and intermediate products identification support the predominance of the ortho-metabolic pathway for phenol degradation. Alginate-entrapped Sphe3 cells completely degraded 1000 mg/L phenol after 192 h, even though phenol catabolism proceeds slower in the first 24 h compared to free cells. Immobilized Sphe3 cells retain phenol-degrading capacity even after 30 days of storage and also can be reused for at least five cycles retaining more than 75% of the original phenol-catabolizing capacity.

Construction of magnetically recoverable MnZnFe2O4@Ag3PO4 Z-scheme photocatalyst for rapid visible-light-driven phenol degradation.

Visible-light-driven magnetic heterojunction as a promising photocatalysts has received much attention in environmental remediation. In this work, novel Z-scheme heterojunction MnZnFe2O4@Ag3PO4 (MZFO@APO) magnetic photocatalysts with excellent visible-light-driven photocatalytic activity are successfully constructed and characterized. The photocatalytic activity for phenol degradation is measured, and photodegradation mechanism is investigated with EPR, radical trapping experiments, and LC-MS. It turns out that the heterojunction introduced MZFO exhibits good adsorption effect on visible light and the direct Z-scheme bandgap alignment of MZFO and APO significantly improves charge separation and electron transfer, outperforming that of pure APO. MZFO@APO-40% with 40% APO content shows the rapid photodegradation performance, obtaining a 100% removal efficiency of phenol (25mg L-1) after 12-min visible light irradiation, and its kinetic constants are approximately 25.3 and 4.9 times higher than that of P25 TiO2 and pure APO, respectively. Especially, MZFO@APO-40% also possesses a high magnetic separation property and can be efficiently reused for 5 cycles. Additionally, EPR and radical trapping experiments confirm that h+, O2-, and 1O2 are the main active species in the photocatalytic process. Hydroquinone and small molecular organic acids such as maleic acid and oxalic acid are detected by LC-MS, which further indicates that the pathway of phenol degradation involves hydroxylation, open-ring reactions, and mineralization reactions. The novel addition of MZFO in photocatalyst construction has the potential to promote its application in environmental remediation.

Biologically evolved dual-pathway catalytic pattern indicating an efficient bioremediation strategy for phenol removal

Bioremediation of phenol has been developed for years, however, its actual application is challenged by low efficiency and environmental intolerance. In addition, although multiple phenol degradation pathways have been reported to coexist in bacteria, the potential significance and value have not been clearly revealed. Here, highly efficient phenol catalytic patterns were identified, and multi-pathway catalytic mechanism was investigated. Parageobacillus thermoglucosidasius W-36 employing a dual-pathway pattern exhibited superior degradation performance than P. thermoglucosidasius W-2 that employed a single-pathway pattern. An exogenous copy of degradation pathway in dual-pathway pattern was obtained via horizontal gene transfer. Based on homology modeling and molecular docking, the three-dimensional structures and substrate-binding sites of exogenous key enzymes were distinct from those of isofunctional enzymes encoded by the chromosome. The dual-pathway pattern was expressed in response to substrate levels in a time-dependent manner, indicating that synergistic effect of degradation pathways conferred strain adaptability to high-concentration phenol. Evolutionary analysis showed that the artful single/dual-pathway patterns in this species may be a natural selection phenomenon caused by high-concentration phenol. Collectively, this naturally evolved pattern enlightens the new strategy and feasibility of introducing auxiliary metabolic pathways to improve degradation efficiency of pollutants.

Metabolic Pathway of Phenol Degradation of a Cold-Adapted Antarctic Bacteria, Arthrobacter sp.

Phenol is an important pollutant widely discharged as a component of hydrocarbon fuels, but its degradation in cold regions is challenging due to the harsh environmental conditions. To date, there is little information available concerning the capability for phenol biodegradation by indigenous Antarctic bacteria. In this study, enzyme activities and genes encoding phenol degradative enzymes identified using whole genome sequencing (WGS) were investigated to determine the pathway(s) of phenol degradation of Arthrobacter sp. strains AQ5-05 and AQ5-06, originally isolated from Antarctica. Complete phenol degradative genes involved only in the ortho-cleavage were detected in both strains. This was validated using assays of the enzymes catechol 1,2-dioxygenase and catechol 2,3-dioxygenase, which indicated the activity of only catechol 1,2-dioxygenase in both strains, in agreement with the results from the WGS. Both strains were psychrotolerant with the optimum temperature for phenol degradation, being between 10 and 15 °C. This study suggests the potential use of cold-adapted bacteria in the bioremediation of phenol pollution in cold environments.

Regulation of defects and nitrogen species on carbon nanotube by plasma-etching for peroxymonosulfate activation: Inducing non-radical/radical oxidation of organic contaminants

The structural defects and heteroatom dopants of carbonaceous materials play critical roles in their activation of peroxymonosulfate (PMS) for organic pollutants’ removal. This study uses plasma-etching technology to control the levels of structural defects and nitrogen species in nitrogen-doped carbon nanotubes (N-CNTs) for excellent PMS activation. The vacancy defects, CO, pyrrolic N and graphitic N could be rationally designed by controlling the plasma-etching time. Obviously, the ID/IG (from 0.56 to 0.94) and CO contents (from 0.07 to 0.44 at%) of N-CNTs increase with rising etching time, exhibiting good linear positive correlations with phenol oxidation rates. Furthermore, through active species identification, quantitative structure–activity relationships analysis and theoretical calculations, vacancy defects (adsorbing PMS O1 site) and CO are confirmed to be the active sites for the generation of 1O2, which is major pathway (82%) for phenol degradation. While radicals induced by pyrrolic N and graphitic N adsorbing PMS O2 site are the minor pathway (18%). Overall, this study sheds new light on the crucial roles of defects and N species in inducing PMS non-radical/radical activation by carbocatalyst via efficiently controlled plasma-etching technology.

Valorization of phenol contaminated wastewater for lipid production by Rhodosporidium toruloides 9564T

Phenol is one of the most common hazardous organic compound presents in several industrial effluents which directly affects the aquatic environment. The present study envisaged the phenol biodegradation and simultaneous lipid production along with its underlying mechanism by oleaginous yeast Rhodosporidium toruloides 9564T. Experiments were designed using simulated wastewater by varying phenol concentration in the range of 0.25–1.5 g/L and inoculum size of 1, 5, and 10% with and without glucose. The oleaginous yeast was found to completely degrade up to 0.75 g/L phenol with lipid accumulation of 26.3%. Phenol at > 0.5 g/L severely inhibited the growth of R. toruloides 9564T at 1% and 5% inoculum size. Phenol toxicity up to 0.75 g/L can be overcome by increasing inoculum size to 10%. The maximum specific growth rate (μmax) and phenol degradation rate (qmax) were found to be 0.0717 h−1 and 0.01523 h−1, respectively. The enzymatic pathway study suggested that R. toruloides 9564T follows an ortho cleavage pathway for phenol degradation and lipid accumulation. Phytotoxicty and cytotoxicity tests for treated and untreated samples clearly demonstrated a decline in toxicity of the treated wastewater. R. toruloides brought about an important paradigm shift toward a circular economy in which industrial wastewater is considered a valuable resource for bioenergy production.

Efficient peroxymonosulfate activation of immobilized Fe–N–C catalyst on ceramsite for the continuous flow removal of phenol

Nowadays, developing environmentally friendly catalysts with both low cost and high efficiency was still a challenge in actual organic wastewater purification. Herein, the Fe–N–C catalyst was successfully immobilized on solid waste derived ceramsite for efficient degradation of phenol under continuous flow conditions by activating peroxymonosulfate (PMS). After the introduction of ceramsite, the microstructure of Fe–N–C catalyst was changed from granular structure to worm-like structure, promoting the dispersion of the nanoscale catalyst and providing more reactive sites. Therefore, the phenol removal rate and mineralization rate of the obtained 0.5FNNC within 30 min were up to 96.79% and 71.79%, respectively. In addition, the degradation rate of the optimal composite (0.5FNNC)/PMS system was about 4.06 times higher than that of bare Fe–N–C/PMS system. Intriguingly, the Fe ion leaching from 0.5FNNC during the degradation reaction was significantly lower than bare Fe–N–C owing to the strong catalyst-support chemical bonding. Based on electron paramagnetic resonance, quenching experiments, X-ray photoelectron spectroscopy analysis and electrochemical analysis, it was indicated that the non-radical processes (1O2 and high valent iron-oxo species) should be responsible for the phenol degradation. Meanwhile, the possible phenol degradation pathways were proposed, and the intermediates were evaluated for ecotoxicity by ECOSAR. Finally, a preliminary economic analysis of this process was carried out. Overall, this work would provide a new strategy for the construction of ceramsite based multi-pore composite catalysts and the large-scale application of persulfate oxidation technology in organic wastewater treatment.

Efficient degradation of phenol in aqueous solution by Fe2+/H2O2/CaO2 system

The traditional Fenton treatment of phenol wastewater can achieve a good degradation efficiency. However, this technology requires pH adjustment before and after the treatment, which will corrode the reactor and increase economic loss. In this study, to overcome the disadvantages of traditional Fenton, a synergistic degradation method of phenol in water by adding calcium peroxide (CaO 2 ) in Fenton oxidation was proposed. Under the optimal dosage (Fe 2＋ : H 2 O 2 : CaO 2 = 1 : 2: 1), the COD removal rate (phenol 100 mg/L) reached 95.59% within 15 min. Results showed that the Fe 2 + / H 2 O 2 /CaO 2 system exerted a good degradation efficiency on phenol in a wide pH range (3–11). In addition, studies have showed that adding CaO 2 in Fe 2 + / H 2 O 2 system was more effective to increase the utilization rate of iron ions and H 2 O 2 , and the amount of reactive oxygen species (ROS) in the system was more than when the same amount of H 2 O 2 was added, free radical detection showed that ⋅ OH and system. The effects of anions (Cl − , NO 3 − , SO 4 2 − , and HCO 3 − ) on the performance of Fe 2 + / H 2 O 2 /CaO 2 were studied. Certain amounts of Cl − , SO 4 2 − , and HCO 3 − affected the COD removal rate more than NO 3 − . Finally, the degradation pathway of phenol was proposed based on mass spectra. This study provided a valuable method for the efficient degradation of industrial wastewater. • The addition of CaO 2 significantly improved organics degradation in the Fe 2 + / H 2 O 2 system. • The Fe 2 + / H 2 O 2 /CaO 2 system exerted a good degradation efficiency in a wide pH range (3–11). • Adding CaO 2 to the Fe 2 + /H 2 O 2 system effectively promoted the reduction of Fe 3＋ to Fe 2＋ and improved the utilization rate of iron ions and H 2 O 2 . • ⋅ OH and ⋅ O 2 − were identified as the main active substances in the Fe 2 + / H 2 O 2 /CaO 2 system.

Ball milling-assisted preparation of N-doped biochar loaded with ferrous sulfide as persulfate activator for phenol degradation: Multiple active sites-triggered radical/non-radical mechanism

Designing Fe-carbon catalyst with multiple active sites for persulfate (PS) activation to water purification is challenging. Herein, nitrogen-doped biochar (NBC) loaded with ferrous sulfide (FeS) was synthesized via two-step ball milling. In FeS@NBCBM/PS system, both electron transfer process and reactive oxygen species (ROSs) including SO4⋅−, O⋅H, O2•− and 1O2 contributed to phenol degradation. Surface-bound S(II) not only interacted with PS for generating SO4•−, but also accelerated Fe(III)/Fe(II) circulation by reducing Fe(III). NBC was favorable for phenol adsorption and exposure of oxygen-containing groups, graphitic and pyridinic N active sites, which mediated electron transfer or ROSs formation. Owing to multiple active sites, this system fast achieved almost complete phenol degradation with excellent adaptability to wide pH range of 3–9, high anti-interference capacity to coexisting substances, and was efficient to various water matrices. Furthermore, phenol degradation pathways were elucidated by DFT calculations with intermediate products showing lower toxicity, demonstrating great potentials of proposed system.

Pseudomonas phenolilytica sp. nov., a novel phenol-degrading bacterium.

This study describes a bacterium strain RBPA9 isolated from a municipality waste dumping area capable of degrading phenol, proposed as a novel species ofPseudomonas. Cells are Gram-negative, rod shaped, aerobic and motile. The genome is 3.92Mb, and the G + C content is 64.64%. The overall genome relatedness indices such as in silico DNA-DNA hybridization (isDDH), average nucleotide identity (ANI), and average amino acid identity (AAI) values were below 70% and 95-96%, respectively. Phylogenetic analysis based on genome-wide core genes and 16S rRNA gene sequences revealed that strain RBPA9 clustered withPseudomonas stutzeriATCC 17588T in both the phylogenetic trees. Maximum growth was recorded at 200mg /L concentration of phenol which was consumed within 24h. A gene cluster of phenol degradation pathway was detected. The quantitative real-time PCR (RT-PCR) demonstrated the expression of all the genes required in the meta-cleavage pathway of phenol in RBPA9. Our results reveal that strain RBPA9 represents a novel species for whichPseudomonas phenolilyticasp. nov. is proposed. The type strain is RBPA9T (= TBRC 15231T = NBRC 115284T).

Subsurface hydrocarbon degradation strategies in low- and high-sulfate coal seam communities identified with activity-based metagenomics

Environmentally relevant metagenomes and BONCAT-FACS derived translationally active metagenomes from Powder River Basin coal seams were investigated to elucidate potential genes and functional groups involved in hydrocarbon degradation to methane in coal seams with high- and low-sulfate levels. An advanced subsurface environmental sampler allowed the establishment of coal-associated microbial communities under in situ conditions for metagenomic analyses from environmental and translationally active populations. Metagenomic sequencing demonstrated that biosurfactants, aerobic dioxygenases, and anaerobic phenol degradation pathways were present in active populations across the sampled coal seams. In particular, results suggested the importance of anaerobic degradation pathways under high-sulfate conditions with an emphasis on fumarate addition. Under low-sulfate conditions, a mixture of both aerobic and anaerobic pathways was observed but with a predominance of aerobic dioxygenases. The putative low-molecular-weight biosurfactant, lichysein, appeared to play a more important role compared to rhamnolipids. The methods used in this study—subsurface environmental samplers in combination with metagenomic sequencing of both total and translationally active metagenomes—offer a deeper and environmentally relevant perspective on community genetic potential from coal seams poised at different redox conditions broadening the understanding of degradation strategies for subsurface carbon.

Phenol degradation in waters with high iodide level by layered double hydroxide-peroxodisulfate: Pathways and products

Recently, layered double hydroxide-peroxodisulfate (LDH-PDS) as an advanced oxidation system can effectively remove organics by the pathway of free radical. However, little has been known if there is a potential risk regarding the formation of high toxic iodine byproducts through another pathway when LDH-PDS is used in high iodide waters at coastal areas. Therefore, this study investigated phenol degradation pathways and transformation products to evaluate both removal mechanism and potential risk by LDH-PDS in high iodide waters. The results showed that in LDH-PDS system, with the degradation of PDS, phenol degraded till below detection limit in 1 hr in the presence of iodide, while PDS and phenol were hardly degraded in the absence of iodide, indicating iodide accelerated the transformation of PDS and the degradation of phenol. What is more, it reached the highest phenol removal efficiency under the condition of 100 mg/L LDH, 0.1 mmol/L PDS and 1.0 mmol/L iodide. In LDH-PDS system, iodide was rapidly oxidized by the highly active interlayer PDS, resulting in the formation of reactive iodine including hypoiodic acid, iodine and triiodide instead of free radicals, which contributed rapid degradation of phenol. However, unfortunately toxic iodophenols were detected. Specifically, 2-iodophenol and 4-iodophenol were formed firstly, afterwards 2,4-diiodophenol and 2,6-diiodophenol were produced, and finally iodophenols and diiodophenols gradually decreased and 2,4,6-Triiodophenol were produced. These results indicated that LDH-PDS should avoid to use in high iodide waters to prevent toxic iodine byproduct formation although iodide can accelerate phenol degradation.

Quantitative proteomic analysis reveals the metabolic characteristics and adaptive mechanism of Cupriavidus oxalaticus T2 in the process of simultaneous nitrogen and phenol removal

Phenol and ammonia in wastewater pose a serious threat to ecosystems and human health. However, the currently limited studies on single bacterium simultaneously removing phenol and nitrogen pollution have not fully elucidated the relevant metabolic mechanisms. The differences in proteomic profile after supplementing with phenol and ammonia for 6 and 24 h, respectively, were evaluated to explore the metabolic characteristics and adaptive mechanism of Cupriavidus oxalaticus T2 during the simultaneous removal process of phenol and nitrogen. Results revealed that a new potential phenol para-degradation pathway appeared in T2. Phenol induced changes in nitrogen metabolism, resulting in increased denitrification and decreased synthesis of glutamate from ammonia at 6 h. In addition, phenol exposure enhanced the expression of cytochrome oxidases with high oxygen affinity and increased ATP synthesis. The increase in chemotaxis and flagellar assembly was conducive to the uptake and utilization of phenol. The synthesis of lipoic acid and biotin was also promoted to resist phenol toxicity. Moreover, phenol triggered cellular stress response, thereby leading to the upregulation of anti-stress proteins, such as universal stress protein, iron‑sulfur cluster protein, and chaperones. This study contributes to revealing the metabolic characteristics and adaptive mechanism of T2 during simultaneous nitrogen and phenol removal. SignificancePhenol and ammonia often co-exist in wastewater, causing serious environmental problems. The information on the metabolic mechanism of simultaneously removing these two pollutants by bacteria is insufficient at present. Moreover, phenol is toxic to microbial and causes cells damage. Therefore, exploring the response mechanism of bacteria to phenol stress is conducive to understand their tolerance mechanism to aromatic compounds. In this study, the metabolic characteristics and adaptive mechanism of C. oxalaticus T2 during the simultaneous removal of phenol and nitrogen process were evaluated by comparing the proteome profiles at different stages. The results revealed the degradation pathways of phenol and nitrogen by strain T2. A variety of phenol response mechanisms were determined, including enhanced energy production, improved cell motility, increased the synthesis of lipoic acid and biotin, and combined action of multiple anti-stress proteins. This study is potentially useful to future phenol and nitrogen co-pollution bioremediation strategies and provides insight into the phenolic compound resistance mechanism in bacteria.

Construction of Z-scheme CuFe2O4/MnO2 photocatalyst and activating peroxymonosulfate for phenol degradation: Synergistic effect, degradation pathways, and mechanism

Photocatalysis coupled with sulfate radical-based advanced oxidation process (SR-AOPs) is an efficient strategy to enhance the degradation efficiency of organic pollution. Herein, a Z-scheme CuFe2O4/MnO2 composite catalyst was successfully fabricated by the hydrothermal method. A series of characterizations demonstrated that the higher CuFe2O4 particle dispersion and larger BET surface area of CuFe2O4/MnO2 catalyst contributed to a high catalytic activity toward the phenol removal compared with pure CuFe2O4. The effects of catalyst concentration, pH, and peroxymonosulfate (PMS) concentration were studied according to the Box-Behnken Design (BBD) method. The results indicated that 100 mg/L 100 mL phenol could be degraded completely at 0.5 g/L CuFe2O4/MnO2 catalyst, pH = 4.8 and 0.5 mM PMS within 30 min. Moreover, the excellent reusability and stability of CuFe2O4/MnO2 were indicated by the results of recycling degradation and ion leaching test. The free radical quenching experiments and electron spin resonance (ESR) confirmed that h+, SO4•-, and •OH were the main reaction species for phenol oxidation. Based on the results of gas chromatography-mass spectrometry (GC-MS) and ion chromatography, the degradation pathway of phenol was proposed, and the toxicity of phenol degradation intermediates was evaluated. This work may provide new insights into the design of heterojunction photocatalysts for PMS activation to remove organic pollutants.

The conversion of the nutrient condition alter the phenol degradation pathway by Rhodococcus biphenylivorans B403: A comparative transcriptomic and proteomic approach.

Highly toxic phenol causes a threat to the ecosystem and human body. The development of bioremediation is a crucial issue in environmental protection. Herein, Rhodococcus biphenylivorans B403, which was isolated from the activated sludge of the sewage treatment plant, exhibited a good tolerance and removal efficiency to phenol. The degradation efficiency of phenol increased up to 62.27% in the oligotrophic inorganic medium (MM) containing 500-mg/L phenol at 18 h. R. biphenylivorans B403 cultured in the MM medium showed a higher phenol degradation efficiency than that in the eutrophic LB medium. On the basis of the transcriptomic and proteomic analysis, a total of 799 genes and 123 proteins showed significantly differential expression between two different culture conditions, especially involved in phenol degradation, carbon metabolism, and nitrogen metabolism. R. biphenylivorans B403 could alter the phenol degradation pathway by facing different culture conditions. During the phenol removal in the oligotrophic inorganic medium, muconate cycloisomerase, acetyl-CoA acyltransferase, and catechol 1,2-dioxygenase in the ortho-pathway for phenol degradation showed upregulation compared with those in the eutrophic organic medium. Our study provides novel insights into the possible pathway underlying the response of bacterium to environmental stress for phenol degradation.

Biochar and GAC intensify anaerobic phenol degradation via distinctive adsorption and conductive properties

The roles of biochar and granular activated carbon (GAC) in the enhancement of anaerobic phenol degradation were characterized through batch tests conducted at different phenol concentrations, coupled with adsorption kinetics, microbial community, and in-situ electrochemical analysis. Both biochar and GAC (15 g/L) led to markedly shorter lag times (t0) by adsorbing dissolved phenol, and faster maximum CH4 production rate (Rmax) by triggering direct interspecies electron transfer (DIET) during a two-stage (adsorption then degradation) anaerobic phenol degradation. The high adsorption capacity of GAC helped achieve a shorter t0, but less affected Rmax of subsequent phenol degradation. Compared with GAC, which showed higher conductivity but no redox activity, biochar exhibited higher electron exchange capacity (6.57 μmol e−/g). This higher electron exchange capacity stemmed from the diverse redox-active moieties, which resulted in a more efficient DIET. Meanwhile, the formation of wire-like appendages which linked the enriched DIET partners (such as Syntrophorhabdus and Methanosaeta) on biochar probably futher enhanced the electron transfer. However, hydrogenotrophic methanogenesis was still the main pathway for syntrophic phenol degradation in the suspended sludge. The in-situ analysis also confirmed that biochar and GAC acted as geobatteries and geoconductors, respectively, and that the stimulation of DIET was persistent.

Facet effect of TiO2 nanostructures from TiOF2 and their photocatalytic activity

In this study, special attention is focused on the design of TiO2 morphology and microstructure in the two-step preparation procedure using TiOF2 as a precursor to study their photodegradation mineralization efficiency. Firstly, TiOF2 was synthesized by a simple solvothermal method using titanium(IV) tetrafluoride, which was further used as aprecursor in preparation of anatase 2D nanosheets, octahedral, decahedral, and rectangular prisms shape structures. The as-obtained nanostructures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller surface area analysis (BET), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy and photoluminescence spectroscopy. It was assumed that TiOF2 could be applied as a useful precursor for the preparation of nanostructured TiO2 with defined morphology. Simple controlling of the reaction environment, together with the stabilizing effect of the introduced substrates, resulted in the formation of TiO2 particles with different morphologies and consequently exposed crystal facets. The presence of {001}, {101} and {100} facets influence on their photocatalytic activity but mostly on their mineralization efficiency and the pathway of phenol degradation. From the obtained series, the TiO2 octahedra exposing {101} facets exhibited the highest photoactivity and mineralization efficiency under UV–Vis light irradiation, which decreases as the other facets appear and become more exposed. The obtained results were compared with a computational study on the ∙OH and ∙O2– attack on the phenyl ring. Overall results showed that the surface effects of the photocatalyst could be an influencing factor in both mineralization efficiency and photodegradation products formation.

Raman spectroscopic technique towards understanding the degradation of phenol by sodium persulfate in hot compressed water

Degradation of phenol by sodium persulfate (SPS) in hot compressed water (HCW) was investigated in a lab-built fused quartz tube reactor (FQTR) coupled with Raman spectroscopy system. The species of S2O82−, SO42−, HSO4−, SO32− and HSO3− in the reaction system were qualitatively and quantitatively analyzed by Raman spectroscopy. The hydrothermal stability of phenol and SPS at different temperature and the degradation of phenol by SPS were also studied. The results indicated that phenol was not stable in aqueous solution above 200 °C, and that only SO42− was generated in the hydrolysis of SPS at temperatures below 50 °C, and SO42− and HSO4− were generated at higher temperatures. The maximum conversion rate (90.93%) and mineralization efficiency (38.88%) of phenol by SPS was obtained at reaction temperature of 300 °C with 180 min reaction time. During the degradation of phenol by SPS, HSO4− was the main product and S∗ (not detected by Raman spectroscopy) exhibits a positive correlation with temperature. In addition, a degradation pathway of phenol by SPS was proposed. The degradation data for the kinetic analysis indicated that the reaction followed pseudo first-order kinetics, and the reaction rate constants (ks) were given as k50 °C = 0.0083 min−1, k100°C = 0.0197 min−1, k200 °C = 0.0498 min−1, k300 °C = 0.0619 min−1 and k400°C = 0.0505 min−1 at 30 min reaction. Moreover, the activation energy (12.580 kJ mol−1), the enthalpy change (9.064 kJ mol−1) and the entropy change (−222.104 J mol−1) of the reaction were also calculated.

Impact of the saturation level on the electrochemical regeneration of activated carbon in a single sequential reactor

The removal of non-biodegradable organics from industrial wastewater through adsorption onto activated carbon (AC) is a simple, effective and inexpensive process; however, as with any separation technology there is a need to regenerate the exhausted material. Here, electrochemical regeneration of AC was carried out in a single reactor alternating sequences of adsorption and regeneration. A key finding was that the contaminant (phenol here, as an industrially-relevant pollutant) saturation level of AC in the reactor directly impacts the efficiency of electrochemical regeneration. The regeneration efficiency was 20% lower and unstable with fully saturated AC, which could be explained by different phenol degradation pathways; upon reaching the exhaustion capacity of the reactor, electrochemical regeneration yielded recalcitrant polymers, whereas full mineralization could take place as long as the breakthrough capacity was not exceeded, even removing impurities originally present in the material. This cleaning effect further led to a change of porosity towards mesopores, which further improved mass transfers and resulted in sustained regeneration efficiencies close to 100%, sustained over 10 consecutive cycles. Under optimal conditions, it was thus possible to achieve over 97% phenol removal with energy consumption below 1 kWh kg−1 of AC, outcompeting traditional regeneration processes.

Mg doped CuO–Fe2O3 composites activated by persulfate as highly active heterogeneous catalysts for the degradation of organic pollutants

Mg doped CuO–Fe2O3 composites were hydrothermally synthesized and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. Mg doping improved the catalytic performance of CuO–Fe2O3 for phenol degradation as the removal efficiency of phenol (33 mg/L) reached up to 84.36% within 45 min using 3.2% Mg doped CuO–Fe2O3 when coupled with persulfate (PS) system. The results revealed that Mg doping generated more defects (oxygen vacancies), which result in the generation of more active species during the degradation process. The influence of catalysts and PS dosages were investigated to obtain the optimum conditions. The effects of pH and dissolved oxygen were also evaluated. Increase of solution pH was found to be beneficial for the removal of phenol because of reduced copper leaching at higher pH. However, decrease in dissolved oxygen concentration retarded the degradation of phenol because of the reduced production of O2•-. Based on the quenching experiments and ESR experiments, 1O2, O2•-, ·OH and ·SO4− were confirmed as the active species in the phenol degradation process and a phenol degradation pathway was proposed. Other contaminants such as nitrobenzene (NB), P-nitrophenol (PNP) and P-Chlorophenol (4-CP) could also be removed to some extent using the present catalyst system.