Removal Of 4-chlorophenol Research Articles

Bio-Graphene Foam: A Robust Solution for Adsorptive and Sustainable Chlorophenol Removal from Wastewater

Bio-Graphene Foam: A Robust Solution for Adsorptive and Sustainable Chlorophenol Removal from Wastewater

Efficient Electrocatalytic Hydrodechlorination and Detoxification of Chlorophenols by Palladium-Palladium Oxide Heterostructure.

Electrocatalytic hydrodechlorination is a promising approach for simultaneous pollutant purification and valorization. However, the lack of electrocatalysts with high catalytic activity and selectivity limits its application. Here, we propose a palladium-palladium oxide (Pd-PdO) heterostructure for efficient electrocatalytic hydrodechlorination of recalcitrant chlorophenols and selective formation of phenol with superior Pd-mass activity (1.35 min-1 mgPd-1), which is 4.4 times of commercial Pd/C and about 10-100 times of reported Pd-based catalysts. The Pd-PdO heterostructure is stable in real water matrices and achieves selective phenol recovery (>99%) from the chlorophenol mixture and efficient detoxification along chlorophenol removal. Experimental results and computational modeling reveal that the adsorption/desorption behaviors of zerovalent Pd and PdO sites in the Pd-PdO heterostructure are optimized and a synergy is realized to promote atomic hydrogen (H*) generation, transfer, and utilization: H* is efficiently generated at zerovalent Pd sites, transferred to PdO sites, and eventually consumed in the dechlorination reaction at PdO sites. This work provides a promising strategy to realize the synergy of Pd with different valence states in the metal-metal oxide heterostructure for simultaneous decontamination, detoxification, and resource recovery from halogenated organic pollutants.

Far-UVC (UV222) based photolysis, photooxidation, and photoreduction of chlorophenols using a KrCl-excimer lamp: Degradation, dechlorination, and detoxification

The KrCl-excimer lamp, emitting far-UVC light at 222 nm (UV222), offers a promising alternative to conventional UVC light at 254 nm (UV254) for the photolysis of organic pollutants and the activation of radical sensitizers. This study was aimed to investigate the efficiencies of UV222 in the treatment of halogenated aromatics, focusing on its performance in degradation, dechlorination and detoxification. Chlorophenols, representative recalcitrant and toxic halogenated aromatics, were used as target pollutants. The pathways of direct photolysis, photooxidation and photoreduction under UV222 illumination were compared. UV222 outperformed UV254 in photolyzing chlorophenols (1.4−34.1 times faster), especially protonated chlorophenols, due to substantially higher UV absorption (17.1−108.0 times) and quantum yields (2.1−3.4 times). The quantum yields of chlorophenols were influenced by the inducive electron-withdrawing effect of Cl-substitutes. Moreover, UV222 improved the dechlorination of chlorophenols to 95 % compared to 60 % by UV254. The introduction of radical sensitizer (e.g., H2O2, nitrate, and sulfite) reduced 4-chlorophenol photolysis by competing for UV222 absorption, though the sensitizers partially increased radical oxidation via generating •OH or eaq−. UV222 photolysis of 4-chlorophenol increased the toxicity by 88.6 times through forming toxic intermediates (e.g., hydroquinone and resorcinol). Notably, •OH and eaq− (i.e., UV222/H2O2 and UV222/sulfite) increased the dechlorination and •OH (i.e., UV222/H2O2) detoxified the mixture solution. Moreover, UV222 photolysis remained effective for 4-chlorophenol removal in real paper-mill wastewater, indicating the potential application of KrCl* lamp UV222.

Physicochemical study of the adsorption of chlorophenols on activated carbon using an advanced double layer model

An advanced theoretical analysis was performed to elucidate the adsorption of 2,4-dichlorophenol and 4-chlorophenol on an activated carbon obtained from pine sawdust. In particular, a double layer adsorption model was used to estimate the number of chlorophenols molecules adsorbed per activated carbon functional group, the concentration of active sites from activated carbon surface involved in the adsorption mechanism, the saturation adsorption capacities and interaction energies to form the adsorbate layers on activated carbon. This theoretical investigation showed that the saturation adsorption capacities for the removal of 2,4-dichlorophenol and 4-chlorophenol were 167 and 130 mg/g, respectively. The adsorption of 2,4-dichlorophenol on activated carbon outperformed the 4-chlorophenol adsorption under tested experimental conditions. The adsorption of these compounds was endothermic and governed mainly by van der Waals interactions and hydrogen bonding. The adsorption of 2,4-dichlorophenol on activated carbon was a multimolecular process with the presence of an aggregation process in the aqueous solution, while a multi-docking adsorption mechanism occurred for the removal of 4-chlorophenol. Overall, this study contributes with theoretical insights on the removal of two emerging water pollutants by using activated carbon.

Synergistic enhancement of chlorophenols removal using eco-friendly alginate@montmorillonite hybrid bio-capsules: insights from encapsulation and kinetic release studies

This study investigates the synergistic effects of alginate@montmorillonite (Alg@Mt) hybrid microcapsules for enhancing water purification, focusing on improving the encapsulation of hydrophobic contaminants. Alg@Mt microcapsules were prepared through ionotropic gelation. Characterisation was performed using SEM-EDX, FTIR, XRD, and TGA. Encapsulation efficiency (EE), loading capacity (LC), and release behaviour were also examined. Alg@Mt microcapsules effectively removed phenol and its chlorinated derivatives from water. Incorporating Na-Mt improved structural and thermal properties, EE, and LC. Increasing the clay content to 60% (w/w) raised the EE of phenol and its more hydrophobic derivative, 2,4,6-trichlorophenol, from 39.74 ± 3.1% (w/w) and 63.91 ± 2% (w/w) to 60.56 ± 1.6% (w/w) and 82.28 ± 2.3% (w/w), respectively, with more controlled release rates, following Fickian diffusion mechanism. EE increased with phenolic substances hydrophobicity, while LC and release rates were inversely related. This approach is promising for removing hydrophobic contaminants from water.

Synergy of atomic hydrogen reduction and reactive oxygen species oxidation over confined Mn bifunctional site for electrocatalytic deep mineralization

Traditional reduction or oxidation processes generating one−component free radicals face challenges in deep dechlorination and mineralization of chlorophenols from wastewater. Herein, an efficient electrocatalytic process has been developed, which couples atomic H* reduction with reactive oxidation species (•OH and 1O2) oxidation on a bifunctional cathode for 4 −chlorophenol (4 −CP) removal. The N − doped carbon nanotubes encapsulated manganese nanoparticles was fabricated as cathode, which could generate atomic H* , initiating nucleophilic hydrodechlorination in presence of confined MnO sites. Subsequently, electrophilic oxidation by generating mainly 1O2 on confined Mn7C3 sites and •OH on confined MnO sites, facilitating the oxidative processes. Experimental results and theory calculations demonstrated that reductive dechlorination and oxidative mineralization processes could mutually promote each other, resulting in an enhancement factor of 2.90. At pH 7, this process achieved 100 % removal for 4 −CP, 84 % dechlorination, 76 % total organic carbon (TOC) removal and low energy consumption (0.76 kWh g−1TOC) within 120 min. Notably, TOC for chlorophenols containing Cl substituents at different positions and real lake water containing 4 −CP could be almost completely removed. This research establishes confined non−noble bifunctional active sites that synergistically enhance reductive dechlorination and oxidative degradation processes, holding significant treatment potential for application in deep mineralization of organochlorine from water/wastewater.

Ni-Zn/CeO2 nanocomposites for enhanced adsorptive removal of 4-chlorophenol.

Chlorophenols are one of the major organic pollutants responsible for the contamination of water bodies. This study explores the application of Ni-Zn/CeO2 nanocomposites, synthesized via the aqueous co-precipitation method, as effective adsorbents for the 4-chlorophenol removal from aqueous solutions. The nanocomposites' chemical and structural characteristics were assessed using different physical characterization methods, viz. X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, zeta potential, using a Box-Behnken design within response surface methodology, optimal conditions of pH 3, temperature 20 °C, contact time 120 min, adsorbent dosage 0.05 g, and 4-chlorophenol concentration 50 ppm are identified. Among the nanocomposites tested, NZC 20:10:70, with 20% Ni and 10% Zn, achieves enhanced performance, removing 99.1% of 4-chlorophenol within 2 h. Adsorption kinetics follow the pseudo-second-order model and equilibrium data fit the Freundlich isotherm. Thermodynamic analysis indicates an exothermic and spontaneous process. The adsorption capacity of NZC 20:10:70 shows significant enhancement, growing from 19.85 mg/g at 10 ppm to 96.33 mg/g at 50 ppm initial concentration. Physical characterization confirms NZC 20:10:70's superior properties, including a high surface area of 118.471 m2/g. Evaluating economic viability, NZC 20:10:70 demonstrates robust reusability, retaining 85% efficiency over eight regeneration cycles. These results highlight NZC 20:10:70 as a promising adsorbent for effective and sustainable chlorophenol removal in water treatment.

Asymmetric Ba0.7Sr0.3CoO3-δ/MXene solar evaporators for enhanced treatment of high salinity organic wastewater: Improving salt deposition control and pollutant removal

Solar-driven interfacial evaporation (SIE) utilizes solar thermal energy to produce clean water, addressing the water-energy paradox. However, challenges like photothermal conversion performance and salt deposition limit its adoption. Additionally, when SIE is applied to organic wastewater treatment, volatile organic compounds (VOCs) in the distilled water can diminish water purification efficiency. In this study, we developed a Ba0.7Sr0.3CoO3-δ/MXene composite solar evaporator capable of simultaneous removal of organic matters (93.70 % removal of 4-chlorophenol) with high evaporation performance (1.50 kg m−2 h−1) during the evaporation of salt-containing organic wastewater. The incorporation of Ba0.7Sr0.3CoO3-δ into the composite significantly enhanced the photothermal conversion capacity, improving the evaporation efficiency. The organic pollutant removal activity of Ba0.7Sr0.3CoO3-δ stemmed from lattice oxygen, which was activated by photothermal conversion heat. The incorporation of Ba0.7Sr0.3CoO3-δ and MXene in the solar evaporator significantly enhances the photothermal conversion performance. Additionally, the innovative asymmetric edge structure effectively addresses the salt deposition issue and enables the removal of organic pollutants through in situ utilization of heat generated from photothermal conversion. This approach offers a subtle yet effective strategy for mitigating pollutant accumulation in the solar interfacial evaporation process, ensuring long-term water purification and clean water production.

High performance removal of chlorophenols from an aqueous solution using an enzymatic membrane bioreactor

Organochlorides and particularly chlorophenols are environmental pollutants that deserve special attention. Enzymatic membrane bioreactors may be alternatives for efficiently removing such hazardous organochlorides from aqueous solutions. We propose here a novel enzymatic membrane bioreactor comprising an ultrafiltration membrane GR81PP, electrospun fibers made of cellulose acetate, and laccase immobilized using an incubation and a fouling approach. Configurations of this biosystem exhibiting the highest catalytic activity were selected for removal of 2-chlorophenol and 4-chlorophenol from aqueous solution in an enzymatic membrane bioreactor under various process conditions. The highest removal of chlorophenols, at 88% and 74% for 2-chlorophenol and 4-chlorophenol, respectively, occurred at pH 5 and 30 °C in the GR81PP/cellulose acetate/laccase biosystem with enzyme immobilized by the fouling method. Furthermore, the GR81PP/cellulose acetate/laccase biosystem with enzyme immobilized by the fouling method exhibited significant reusability and storage stability compared with the biosystem with laccase immobilized by the incubation method. The mechanism of enzyme immobilization is based on pore blocking and cake-layer formation, while the mechanism of chlorophenols removal was identified as a synergistic combination of membrane separation and enzymatic conversion. The importance of the conducted research is due to efficient removal of hazardous organochlorides using a novel enzymatic membrane bioreactor. The study demonstrates the biosystem's high catalytic activity, reusability, and stability, offering a promising solution for environmental pollution control.

Salt assistant bimetallic sludge-derived porous carbon for efficient peroxymonosulfate activation

The development of cost-effective, environmentally benign, and high-performance peroxymonosulfate (PMS) activation towards wastewater treatment is still considered a challenge. In this work, the sludge-derived porous carbon loaded with bimetal oxides (DSC-FeMn) was fabricated by molten salt assistant strategy using the combination of zinc chloride, metal ions and Fe containing sludge. The obtained DSC-FeMn exhibited high catalytic activity for nearly 100 % 4-chlorophenol (4-CP) removal within 30 min with the k of 0.304 min−1, which was 1.07 and 11.94 times that of the single Fe and Mn-sludge-derived carbon (DSC-Fe, DSC-Mn), respectively. Quenching experiments, electron paramagnetic resonance tests (EPR), X-ray photoelectron spectroscopy (XPS), H2-temperature programmed reduction (H2-TPR) and electrochemical experiments proved that the radical pathway, dominated by OH and SO4−, led to the excellent degradation performance of DSC-FeMn, which was attributed to the redox cycling between Fe and Mn. This study provides a new idea for sludge resource utilization, and it deepens the understanding of the mechanism of PMS activation by the synergistic interaction between bimetal.

Enhanced hydrodechlorination of 4-chlorophenol through carboxymethylcellulose-modified Pd/Fe nanosuspension synthesized by one-step methods

Palladized iron (Pd/Fe) represents one of the most common modification strategies for nanoscale zero-valent iron (nZVI). Most studies prepared Pd/Fe by reducing iron salts and depositing Pd species on the surface of pre-synthesized nZVI, which can be called the two-step method. In this study, we proposed a one-step method to obtain Pd/Fe by the concurrent formation of Fe0 and Pd0 and investigated the effects of these two methods on 4-chlorophenol (4-CP) removal, with carboxymethylcellulose (CMC) coated as a surface modifier. Results indicated that the one-step method, not only streamlined the synthesis process, but also Pd/Fe-CMCone-step, synthesized by it, exhibited a higher 4-CP removal rate (97.9%) compared to the two-step method material Pd/Fe-CMCtwo-step (82.4%). Electrochemical analyses revealed that the enhanced activity of Pd/Fe-CMCone-step was attributed to its higher electron transfer efficiency and more available reactive species, active adsorbed hydrogen species (Hads*). Detection of intermediate products demonstrated that, under the influence of Pd/Fe-CMCone-step, the main route of 4-CP was through hydrodechlorination (HDC) to form phenol and H* was the main active specie, supported by EPR tests, quenching experiments and product analysis. Additionally, the effects of initial 4-CP concentration, initial pH, O2 concentration, anions such as Cl−, SO42−, HCO3−, and humic acid (HA) were also investigated. In conclusion, the results of this study suggest that Pd/Fe-CMCone-step, synthesized through the one-step method, is a convenient and efficient nZVI-modifying material suitable for the HDC of chlorinated organic compounds.

Delving into the Impacts of Different Easily Degradable Carbon Sources on the Degradation Characteristics of 2,4,6-Trichlorophenol and Microbial Community Properties

In chlorophenol wastewater treatment, adding easily degradable carbon sources, such as methanol, ethanol, sodium acetate, and sodium propionate, significantly improves the chlorophenol removal efficiency. This study systematically compares these conventional carbon sources in different sequencing batch reactors to understand their specific effects on both 2,4,6-trichlorophenol (2,4,6-TCP) degradation efficiency and microbial abundance. In a 35-day experiment, as a carbon source, ethanol exhibited a lower 2,4,6-TCP degradation concentration (77.56 mg/L) than those of methanol, sodium acetate, and sodium propionate, which achieved higher degradation concentrations: 123.89 mg/L, 170.96 mg/L, and 151.79 mg/L, respectively. As a carbon source, sodium acetate enhanced extracellular polymeric substance production (200.80 mg/g·VSS) by microorganisms, providing protection against the toxicity of chlorophenol and resulting in a higher 2,4,6-TCP removal concentration. Metagenomics identified crucial metabolic genes, including PcpA, chqB, Mal-r, pcaI, pcaF, and fadA. The abundance of genera containing the chqB gene correlated positively with the metabolic capacity for 2,4,6-TCP. Moreover, small molecular carbon sources such as methanol, sodium acetate, and sodium propionate promoted the enrichment of genera with functional genes.

Electrocatalytic denitrification biofilter for advanced purification of chlorophenols via ceramsite-based Ti/SnO2–Sb particle electrode: Performance, microbial community structure and mechanism

In response to the demand for advanced purification of industrial secondary effluent, a new method has been developed for treating chlorophenol wastewater using the novel ceramsite-based Ti/SnO2–Sb particle electrodes (Ti/SnO2–Sb/CB) enhanced electrocatalytic denitrification biofilter (EDNBF-P) to achieve removal of chlorophenols (CPs), denitrification, and reduction of effluent toxicity. The results showed that significantly improved CPs and TN removal efficiency at low COD/N compared to conventional denitrification biofilter, with CPs removal rates increasing by 0.33%–59.27% and TN removal rates increasing by 12.53%–38.92%. Under the conditions of HRT = 2h, 3V voltage, charging times = 12h, and 25 °C, the concentrations of the CPs in the effluent of EDNBF-P were all below 1 mg/L, the TN concentration was below 15 mg/L, while the effluent toxicity reached the low toxicity level. Additionally, the Ti/SnO2–Sb/CB particle electrodes effectively alleviated the accumulation of NO2−-N caused by applied voltage. The Silanimonas, Pseudomonas and Rhodobacter was identified as the core microorganism for denitrification and toxicity reduction. This study validated that EDNBF-P could achieve synergistic treatment of CPs and TN through electrocatalysis and microbial degradation, providing a methodological support for achieving advanced purification of chlorophenol wastewater with low COD/N in industrial applications.

Oil palm frond-derived cellulose nanocrystals: Effect of pretreatment and elucidating its reinforcing potential in hydrogel beads

Herein, cellulose nanocrystals were synthesized from oil palm fronds (CNC-OPF) involving two pretreatment approaches, viz. autohydrolysis and soda pulping. The pretreatments were applied individually to OPF fibers to assess their influence on CNCs' physicochemical and thermal properties. CNC-OPF samples were assessed using complementary characterization techniques, which confirmed their purity and characteristics. CP/MAS 13C NMR and TEM studies revealed that autohydrolysis pretreatment yielded CNCs with effective hemicellulose and extractives removal compared to that of soda pulping. XRD analysis demonstrated that autohydrolysis-treated CNC-OPF contained a much higher crystallinity index compared to soda pulping treatment. BET measurement disclosed a relatively higher surface area and wider pore diameter of autohydrolysis-treated CNC-OPF. Autohydrolysis-treated CNCs were applied as a reinforcement filler in alginate-based hydrogel beads for the removal of 4-chlorophenol from water, which attained a qmax of 19.168 mg g−1. BET analysis revealed the less porous nature of CNC-ALG hydrogel beads which could have contributed to hydrogel beads' relatively lower adsorption capacity. The point of zero charge of CNC-ALG hydrogel beads was 4.82, suggesting their applicability only within a short solution pH range. This study directs future studies to unveil the possibilities of functionalizing CNCs in order to enhance the adsorption performance of CNC-immobilized hydrogel beads towards 4-chlorophenol and other organic contaminants.

Photochemical-promoted ZVI reduction for highly efficient removal of 4-chlorophenol and Cr(VI): Catalytic activity, performance and electron transfer mechanisms

Zero-valent iron (ZVI) reduction represents a promising methodology for water remediation, but its broad application is limited by two critical challenges (i.e., aggregation and passivation). Here, we report a hybrid strategy of photochemical-promoted ZVI reduction with high efficiency and reduction capacity for removing coexisting refractory pollutants in water. A composite material with Pd/Fe bimetallic nanoparticles supported onto semiconducting metal oxide (Pd/Fe@WO3-GO) was prepared and subsequently used as the model catalyst. By using the developed strategy with visible light as light source, this catalyst showed a remarkable catalytic performance for simultaneously eliminating 4-chlorophenol (4-CP) and Cr(VI), with dehalogenation rate as high as 0.43 min−1, outperforming the reported ZVI-based catalysts. A synergistic interaction of photocatalysis and ZVI reduction occurred in this strategy, where the interfacial electron transfer on particles surface were greatly strengthened with light irradiation. The activation was attributed to the dual functions of semiconducting material as support to disperse Pd/Fe nanoparticles and as (photoexcited) electron donor to directly trigger reduction reactions and/or indirectly inhibit the formation of oxides passivation layer. Both direct electron transfer and H*-mediated indirect electron transfer mechanisms were confirmed to participate in the reduction of pollutants, while the later was quantitatively demonstrated as the predominant reaction route. Importantly, this strategy showed a wide pH applicability, long-term durability and excellent catalytic performance in different real-water systems. This work provides new insights into ZVI reduction and advances its applications for the removal of combined organic and inorganic pollutants. The developed photochemical-promoted ZVI reduction strategy holds a great potential for practical applications.

A photocatalyst with an enhanced Schottky effect and an efficient electron-transfer channel fabricated by assembling Ni–WC heterojunction nanoparticles on g-C3N4 for highly efficient removal of chlorophenols

An enhanced Schottky effect and efficient electron-transfer channel in Ni–WC/CN enable the efficient separation and transfer of photoexcited electrons, which boosts efficient photocatalytic degradation of toxic 4-chlorophenol.

Optimized preparation of nitrogen-modified ceria for stable and efficient degradation of 2,4-DCP

Chlorophenols have been frequently detected in the environment, posing potential threats to both the natural ecosystem and human health. Semiconductor photocatalytic degradation of chlorophenols has become a prominent research focus. However, the development of high-performance and stable photocatalysts remains challenging. In this work, the nitrogen-modified ceria (N-CeO2) was optimally prepared by microwave-assisted method and utilized for photocatalytic degradation of 2,4-DCP. The CeO2 photocatalyst with 10% nitrogen doping (10% N-CeO2) prepared under the optimal condition (microwave power of 560 W for 2 min and calcination temperature of 400 °C for 2 h) degraded 2,4-DCP with the highest removal efficiency of 93.51%. It was identified that the optimally prepared 10% N-CeO2 photocatalyst had the nanometer size with surface imperfections and increased BET surface, and showed strongest photocurrent response and lowest charge transfer resistance among all the prepared materials. Additionally, an analysis of the band gap structure revealed that the band gap of 10% N-CeO2 decreased from 3.05 eV (for pure CeO2) to 2.42 eV, resulting in enhanced light absorption capacity. The radical trapping experiments and electron paramagnetic resonance (EPR) proved that the active species contributed to the degradation of 2,4-DCP mainly as •OH, •O2-. The potential photocatalytic degradation mechanism of 2,4-DCP was a continuous dechlorination and hydroxylation process with complete mineralization of the pollutant to CO2 and H2O. This work can provide a feasible way to prepare high-efficiency nitrogen-doped ceria photocatalysts with great potential for the removal of chlorophenols.

Aluminum Montmorillonite/Polyaniline Hybrid Composite-Based Organogels for the Expurgation of Carcinogenic Chlorophenols and Congo Red Dye from Defiled Water Sources.

Chlorophenol and Congo Red dye being highly toxic are well known for their carcinogenic activity. This work focuses on preparing an organogel for the removal of both chlorophenol and Congo Red. PAni molecules were grafted in situ between the layers of montmorillonite (MMT) to form a PAni/MMT composite, which was further modified to form a gel structure. The composite was thoroughly characterized by high-resolution X-ray diffraction (HR-XRD), Fourier transform infrared (FT-IR) analysis, Brunauer-Emmett-Teller (BET) analysis, and thermogravimetric analysis (TGA). The gel was further analyzed by scanning electron microscopy (SEM) and by studying the rheological properties. The resulting gel exhibited an impressive solvent uptake, with a maximum of 2084% (20 times) for chlorophenol, while the dye adsorption capacity was 349.72 mg/g with 99.44% removal efficiency. The adsorption proceeded with the pseudo-second-order model followed by the Langmuir monolayer adsorption model and Weber's intraparticle diffusion model. The sorbent was found to be selective among cationic dyes while retaining 83% of dye even in the fifth cycle. The hybrid sorbent shows great promise for sustainable purposes, and the results of this study are certainly encouraging.

Feasibility Study of Using Excess Sludge Fermentation Broth as a Co-Metabolic Carbon Source for 2,4,6-Trichlorophenol Degradation

Excess sludge fermentation is a commonly employed method for carbon sources in wastewater treatment plants, but its use as a carbon source for chlorophenol removal has been relatively underexplored. In this study, a laboratory-scale sludge fermentation SBR (FSBR) was integrated with a 2,4,6-trichlorophenol (2,4,6-TCP) degradation SBR (DSBR), resulting in a stable removal of 2,4,6-TCP without the need for external carbon sources. In this coupled system, the concentrations of volatile fatty acids in FSBR remained constant, with acetic acid, propionic acid, butyric acid, and valeric acid concentrations reaching 322.04 mg COD/L, 225.98 mg COD/L, 274.76 mg COD/L, and 149.58 mg COD/L, respectively, and the acid production efficiency increased to 88.40%. Throughout the 110-day operational period, the activated sludge concentration in the DSBR was consistently maintained at 3021 ± 110 mg/L, and the sludge SVI remained stable at 70 mL/g. The maximum amount of 2,4,6-TCP removed reached 240.13 mg/L within a 12 h operating cycle. The use of excess sludge fermentation can completely replace commercial carbon sources for 2,4,6-TCP removal, leading to cost savings in chlorophenol treatment and broadening the applicability of this technology.

Adaptive laboratory evolution of Rhodococcus rhodochrous DSM6263 for chlorophenol degradation under hypersaline condition

BackgroundNormally, a salt amount greater than 3.5% (w/v) is defined as hypersaline. Large amounts of hypersaline wastewater containing organic pollutants need to be treated before it can be discharged into the environment. The most critical aspect of the biological treatment of saline wastewater is the inhibitory/toxic effect exerted on bacterial metabolism by high salt concentrations. Although efforts have been dedicated to improving the performance through the use of salt-tolerant or halophilic bacteria, the diversities of the strains and the range of substrate spectrum remain limited, especially in chlorophenol wastewater treatment.ResultsIn this study, a salt-tolerant chlorophenol-degrading strain was generated from Rhodococcus rhodochrous DSM6263, an original aniline degrader, by adaptive laboratory evolution. The evolved strain R. rhodochrous CP-8 could tolerant 8% NaCl with 4-chlorophenol degradation capacity. The synonymous mutation in phosphodiesterase of strain CP-8 may retard the hydrolysis of cyclic adenosine monophosphate (cAMP), which is a key factor reported in the osmoregulation. The experimentally verified up-regulation of intracellular cAMP level in the evolved strain CP-8 contributes to the improvement of growth phenotype under high osmotic condition. Additionally, a point mutant of the catechol 1,2-dioxygenase, CatAN211S, was revealed to show the 1.9-fold increment on activity, which the mechanism was well explained by molecular docking analysis.ConclusionsThis study developed one chlorophenol-degrading strain with extraordinary capacity of salt tolerance, which showed great application potential in hypersaline chlorophenol wastewater treatment. The synonymous mutation in phosphodiesterase resulted in the change of intracellular cAMP concentration and then increase the osmotic tolerance in the evolved strain. The catechol 1,2-dioxygenase mutant with improved activity also facilitated chlorophenol removal since it is the key enzyme in the degradation pathway.