Chlorophenols in textile dyeing sludge: Pollution characteristics and environmental risk control

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.

Removal of mixed pollutants of perfluorooctanoic acid and 2,4,6-trichlorophenol via adsorption-photocatalysis using Ga2O3-Bi4O7 combining with fluorine-doped covalent triazine framework: Role of different active species

Perfluorooctanoic acid (PFOA) and 2,4,6-trichlorophenol (2,4,6-TCP) are significant pollutants found in textile wastewater, posing severe threats to ecological environments. The construction of an adsorption-photocatalytic system enables the efficient removal of mixed pollutants by harnessing their synergistic effect, thereby overcoming the limitations of removing mixed pollutants with single water treatment technologies. Herein, fluorine-doped covalent triazine framework (F-CTF) was combined with Ga2O3-Bi4O7 heterojunction to obtain Ga2O3-Bi4O7/F-CTF (GaBi/CTF). F-CTF greatly facilitates the adsorption process and provides convenience for photocatalysis. Simultaneously, the excellent conductivity of F-CTF promoted the separation of photoinduced charge carriers in Ga2O3-Bi4O7. GaBi/CTF5 (5 is the mass percentage of F-CTF) showed excellent degradation performance, and the removal rates of PFOA and 2,4,6-TCP reached 93.0 % and 100.0 % within 90 min, respectively. Mechanistic analysis revealed that 2,4,6-TCP and PFOA were attacked by distinct active species because of the disparate characteristics. The presence of phenolic hydroxyl groups makes 2,4,6-TCP more vulnerable to superoxide radicals (·O2-) and hydroxyl radicals (·OH), whereas PFOA is oxidized by holes (h+). The coexistence of mixed pollutants with diverse characteristics enables optimal utilization of active species generated within photocatalytic system. Moreover, the good stability of GaBi/CTF5 provides a feasible solution for efficient treatment of mixed pollutants in textile wastewater.

Investigation of the speciation and environmental risk of heavy metals in biochar produced from textile sludge waste by pyrolysis at different temperatures

The aim of the present study was to find environmentally friendly solutions for the disposal of problematic and toxic textile sludge (TS) by producing textile sludge biochar (TSB) by pyrolysis and evaluating its chemical properties, polycyclic aromatic hydrocarbon (PAH) content, heavy metals (HMs) speciation, environmental risks, and effects on seed germination. Pyrolysis of TS at temperatures ranging from 300 to 700 °C significantly reduced (85-95%) or eliminated certain PAHs in the biochar, enriched heavy metal content within land use limits, and increased bioavailability of HMs in biochar produced at 300 °C and decreased leaching capacity of HMs in biochar produced at 700 °C. The speciation of HMs and their bioavailability during pyrolysis processes was strongly temperature dependent, with lower temperatures increasing the toxic and bioavailable forms of Zn and Ni, while higher temperatures converted the bioavailable Ni to a more stable form, while Cu, Cr, and Pb were transformed from stable to toxic and bioavailable forms. The ecological risk index (RI) values of TSB-300 and TSB-700 are below the threshold value of 150, indicating a low-risk level, and the risk level decreases at temperatures above 500 °C. Further, the extracts of TSB-300 and TSB-700 had the highest percentage of germinating seeds, while the extracts of TS and TSB-500 inhibited seed germination by 20-30% compared to the control. These results indicate that pyrolysis effectively reduces PAHs and binds leachable HMs in biochar, however, the specific pyrolysis temperature influences metal speciation, bioavailability, seed germination, and environmental risk.

Utilizing sludge-based activated carbon for targeted leachate mitigation in wastewater treatment

Activated carbon (AC) based adsorbents derived from waste sludge were utilized to remediate mixed contaminants in wastewater as an integrated waste-to-resource approach promoting a paradigm shift in management of refuse sludge and wastewater. This review specifically focuses on the remediation of constituents of landfill leachate by sludge-based activated carbon (SBAC). The adsorption effectiveness of SBAC for the exclusion of leachate characters including heavy metals, phenols, dyes, phosphates, and phosphorus were explored with regard to modifiers such as pH, temperature, properties of the adsorbent including functional groups, initial doses of absorbent and adsorbate, and duration of exposure to note the impact of each parameter on the efficiency of adsorption of the sludge adsorbent. Through the works of various researchers, it was noted that the properties of the adsorbent, pH and temperature impact the working of SBACs. The pH of the adsorbent by influencing the functional groups. Temperature was expected to have a paramount effect on the adsorption efficiency of the SBACs. The importance of the regeneration and recycling of the adsorbents as well as their leachability is highlighted. Sludge based activated carbon is recommended as a timely, resource-efficient, and sustainable approach for the remediation of wastewater.

Effective separation of dyes/salts by sulfonated covalent organic framework membranes based on phenolamine network conditioning

This study developed a modified polyacrylonitrile (PAN) membrane controlled by a phenol-amine network and enhanced with a sulfonated covalent organic framework (SCOF), aimed at improving the efficiency of textile wastewater treatment. Utilizing a phenol-amine network control strategy allows for precise manipulation of interfacial reactions in the synthesis of SCOF, achieving highly uniform modification on the surface of the PAN membrane. This modified membrane demonstrated high rejection of over 98% for various water-soluble dyes, including Alcian blue 8GX, Coomassie Brilliant Blue G250, methyl blue, congo red, and rose bengal, and also exhibited specific selectivity in processing salt-containing wastewater. By adjusting the deposition time of the phenol-amine and the concentration of SCOF monomers, optimal retention performance and permeate flux were achieved, effectively separating dyes and salts. This research provides a new and effective solution for treating textile wastewater, especially in separating and recovering dyes and salts, offering broad application prospects in environmental management and water resource management, and highlighting its significant practical implications.

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.

Fabrication of a PCN/BiOBr 2D hybrid with improved photocatalytic performance of 2,4-dichorophenol degradation

Photocatalysis has received much attention as an environmentally friendly route to manage the emerging organic pollution problems. Herein, BiOBr nanosheets have been synthesized by a hydrothermal method, and then PCN/BiOBr hybrids are designed via a facile wet chemical method. The as-prepared PCN/BiOBr hybrids are characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (UV-vis DRS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The PCN/BiOBr composite exhibits remarkable improved activity in the degradation of 2,4-dichlorophenol (2,4-DCP) as compared to the pristine BiOBr. Based on the ·OH amount-related fluorescence spectra fluorescence and the photoelectrochemistry (PEC) tests, it is confirmed that the enhanced photocatalytic performance of PCN/BiOBr is attributed to the promoted charge separation. Moreover, by means of the radical-trapping experiments it is demonstrated that the formed ·O2- species, as the electron-modulated direct products, are the primary active species during the photocatalytic degradation of 2,4-DCP. This work would provide a feasible design strategy to fabricate high-activity photocatalysts for 2,4-DCP degradation.

Enhanced Hydrosaturation Selectivity and Electron Transfer for Electrocatalytic Chlorophenols Hydrogenation on Ru Sites

Electrocatalytic hydrogenation is acknowledged as a promising strategy for chlorophenol dechlorination. However, the widely used Pd catalysts exhibit drawbacks, such as high costs and low selectivity for phenol hydrosaturation. Herein, we demonstrate the potential and mechanism of Ru in serving as a Pd substitute using 2,4,6-trichlorophenol (TCP) as a model pollutant. Up to 99.8% TCP removal efficiency and 99% selectivity to cyclohexanol, a value-added compound with an extremely low toxicity, were achieved on the Ru electrode. In contrast, only 66% of TCP was removed on the Pd electrode, with almost no hydrosaturation selectivity. The superiority of Ru over Pd was especially noteworthy in alkaline conditions or the presence of interfering species such as S2-. The theoretical simulation demonstrates that Ru possesses a hydrodechlorination energy barrier of 0.72 eV, which is comparable to that on Pd. Meanwhile, hydrosaturation requires an activation energy of 0.69 eV on Ru, which is much lower than that on Pd (0.92 eV). The main reaction mechanism on Ru is direct electron transfer, which is distinct from that on Pd (indirect pathway via atomic hydrogen, H*). This work thereby provides new insights into designing cost-effective electrocatalysts for halogenated phenol detoxification and resource recovery.

Fabrication of Multifunctional Cotton Fabrics with Antibacterial, Hydrophobic, and Dyeing Performance

Cotton fibers have received considerable attention owing to their functional properties. Current research endeavors have shifted toward devising straightforward and versatile approaches for modifying cotton fibers. Herein, a simple and feasible method was proposed for preparing multifunctional cotton fibers. This method entailed subjecting cotton fibers to alkaline conditions, prompting the epoxy group in epoxidized soybean oil to engage in a ring-opening reaction with the hydroxyl group in cotton fibers and the amino group in polyhexamethylene guanidine hydrochloride. Epoxidized soybean oil acted as a bridge, forming a covalent bond between polyhexamethylene guanidine hydrochloride and cotton fibers, thereby facilitating the cationization of cotton fibers. Structural changes in the modified cotton fibers were characterized using Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy. The modified cotton fibers were also evaluated for their dyeing, antibacterial, and hydrophobic properties. The results demonstrated that the dye exhaustion and total dye utilization of modified cotton in salt-free dyeing were much higher than those of raw cotton in conventional dyeing. The water contact angle of the modified cotton fiber reached 139.5°, and their antibacterial properties were partially improved. Importantly, this chemical modification was performed under mild conditions, highlighting its simplicity and environmentally friendly nature.

Synthesis and applications of biomass-derived porous carbon materials in energy utilization and environmental remediation

Renewable biomass and its waste are considered among the most promising applications materials owing to the depletion of fossil fuel and concerns about environmental pollution. Notably, advanced porous carbon materials derived from carbon-rich biomass precursors exhibit controllable pore structures, large surface areas, natural microstructures, and abundant functional groups. In addition, these three-dimensional structures provide sufficient reaction sites and fascinating physicochemical properties that are conducive to heteroatom doping and functional modification. This review systematically summarizes the design methods and related mechanisms of biomass-derived porous carbon materials (BDPCMs), discusses how the synthesis conditions influence the structure and performance of the carbon material, and emphasizes the importance of its use in energy utilization and environmental remediation applications. Current BDPCMs challenges and future development strategies are finally discussed to provide systematic information for further synthesis and performance optimization, which are expected to lead to novel ideas for the future development of bio-based carbon materials.

Zinc nanoparticles encapsulated in porous biopolymer beads for reduction of water pollutants and antimicrobial activity

This work focuses on the preparation of composite beads from alginate crosslinked with copper at several loading percent and also loaded with ZnNPs. Th obtained samples were applied as catalysts for the reduction of the organic polluants 4-NP, MB, OG, MO, and CR in simple and binary systems. XRD results and TEM images confirmed the presence of ZnNPs in the polymer matrix. XRF and TGA analysis showed that the percentage of the cross-linking agent significantly influences the content of ZnNPs as well as the thermal stability of the resulting material. The catalytic activity of the composite beads showed that the Cu(4 %)-ALG(ZnNPs) sample was the best catalyst for all pollutants. In the simple system, the recorded rate constants for MB, MO, 4-NP, OG, and CR were 0.0133 s-1, 0.0076 s-1, 0.005 s-1, 0.0042 s-1, 0.0036 s-1, respectively. The catalyst was more selective towards the cationic MB dye for binary systems. For antibacterial and antifungal applications, the different materials containing ZnNPs and their counterparts containing Zn2+ were found to be active across all bacterial strains (Gram positive and Gram negative) as well as fungi, and the Zn2+-containing composites in particular performed better across all bacteria and fungi.

Deciphering ligninolytic enzymes in the secretome of Pycnoporus sp. and their potential in degradation of 2-chlorophenol

Chlorophenols and their derivatives are persistent environmental pollutants, posing a threat to terrestrial and aquatic life. The biological approach for eliminating toxic contaminants is an effective, sustainable, and environmental friendly method. In this study, the crude enzymes present in the secretome of white-rot fungus (Pycnoporus sp.) were explored for the degradation of 2-chlorophenol. The activity of ligninolytic enzymes in the secretome was analyzed and characterized for their kinetics and thermodynamic properties. Laccase and manganese peroxidase were prevalent ligninolytic enzymes and exhibited temperature stability in the range of 50-65 °C and pH 4-5, respectively. The kinetic parameters Michaelis constant (Km) and turnover number (Kcat) for Lac were 42.54 μM and 45 s-1 for 2,2'-azino-bis (3-ethylben- zothiazoline-6-sulfonic acid), and 93.56 μM and 48 s-1 towards 2,6-dimethoxyphenol whereas Km and Kcat for MnP were 2039 μM and 294 s-1 for guaiacol as substrate. Treatment with the crude enzymes laccase and manganese peroxidase results in the reduction of 2-chlorophenol concentration, confirmed by UV-visible absorption spectra and high-performance liquid chromatography analysis. The detoxification of 2-chlorophenol into less toxic forms was confirmed by the plate toxicity assay. This study demonstrated that crude enzymes produced by Pycnoporus sp. could potentially minimize the toxicity of phenolic compounds in a sustainable way.

Microwave assisted and conventional hydrothermal treatment of waste seaweed: Comparison of hydrochar properties and energy efficiency

Waste seaweed is a valuable source for converting into value-added carbon materials. In this study, the production of hydrochar from waste seaweed was optimized for hydrothermal carbonization in a microwave process. The produced hydrochar was compared with hydrochar synthesized by the regular process using a conventional heating oven. The results show that hydrochar produced with a holding time of 1 h by microwave heating has similar properties to the hydrochar produced in a conventionally heated oven for 4 h (200 °C and water/biomass ratio 5): carbon mass fraction (52.4 ± 3.9 %), methylene blue adsorption capacity (40.2 ± 0.2 mg g^-1) and similar observations on surface functional groups and thermal stability were made between hydrochars produced by both methods. The analysis of energy consumption showed microwave assisted carbonization consume higher energy in compare to conventional oven. The present results suggest that hydrochar made from waste seaweed and using the microwave technique could be an energy-saving technology for producing hydrochar with similar specifications to hydrochar produced by conventional heating methods.

Design a flower-like magnetic graphite carbon microsphere for enhanced adsorption of 2,4-dichlorophenol

2,4-Dichlorophenol (2,4-DCP) is a hazardous chlorinated organic chemical, so its removal is an important task to protect the whole ecosystem and human health. During the material preparation, the magnetic graphitic carbon adsorbent (HFMCM) with a sparse sheet-like stacking structure was formed by interlayer assembly of nickel hydroxide nanosheets and hydrothermal glucose carbon. The conditions for optimal performance of the adsorbent are 45 °C and pH 5. The maximum adsorption capacity of HFMCM-180 for 2,4-DCP is 147.06 mg·g^-1. Adsorption behavior in accordance with Langmuir isothermal model and pseudo-second-order kinetic models. The adsorbent remains selective for 2,4-DCP in metal ion solutions. More than 75% of the adsorption capacity is maintained after five cycles of adsorption. Electrostatic interaction, hydrogen bonding, and π-π bonding play a major role in the adsorption of 2,4-DCP by HFMCM. The adsorbent was glucose as the carbon source, nickel sulfate as the magnetic source, and hexamethylenetetramine as the precipitant. Its carbonization after pretreatment with different hydrothermal temperatures resulted in the synthesis of flower-like graphitic carbon spheres with magnetic properties. The interconnected pore channels on the adsorbent surface conferred large specific surface area to the material. 2,4-DCP was efficiently adsorbed by π-π stacking, hydrogen bonding, and electrostatic attraction within the pore channels with low spatial potential resistance.

Formation and transformation of reactive species in the Fe2+/peroxydisulfate/Cl- system

The influence of Cl^- on the formation mechanism of active components is often neglected in the Fe²⁺/peroxydisulfate (PDS) system containing a large amount of ferryl ion reactive specie (Fe(Ⅳ)). In the current investigation, the effects of Cl^- concentration on the removal of methyl phenyl sulfoxide (PMSO), the formation of methyl phenyl sulfone (PMSO₂), the transformation of reactive species and oxidation products were investigated under different reaction conditions that included Fe²⁺ dosage, PDS dosage, and pH₀. The results showed that Cl^- complexing Fe²⁺ increased the formation path of sulfate radical (SO₄^·-) in the Fe²⁺/PDS system. Fe²⁺ dosage and pH₀ value affected the content and morphology of Fe²⁺-Cl^- complex, thus affecting the composition of reactive species. According to the experiment of free radical steady-state concentration, it was found that low concentration of Cl^- reacted with SO₄^·- and increased the steady-state concentration of chlorine radicals (8.09 × 10^-13 M [·Cl]_ss at 1.41 mM Cl^-), while at high concentration of Cl^-, the contents of SO₄^·-, hydroxyl radical (·OH) and dichloride anion radicals (Cl₂^·-) increased and the contents of Fe(Ⅳ) and ·Cl decreased. ·Cl had strong reactivity with PMSO, and PMSO and its oxidation products were chlorinated under the combined action of ·Cl and Cl₂^·-. This work reveals the reaction mechanism and environmental application risks of Fe²⁺/PDS technology and lays the groundwork for subsequent industrial application of Fe²⁺/PDS system.

Efficient removal of sixteen priority polycyclic aromatic hydrocarbons from textile dyeing sludge using electrochemical Fe2+-activated peroxymonosulfate oxidation-A green pretreatment strategy for textile dyeing sludge toxicity reduction

It is urgent to remove polycyclic aromatic hydrocarbons (PAHs) from textile dyeing sludge (TDS) before its final deposal due to their recalcitrant nature and generation of toxic byproducts during TDS treatment. In this study, an electrochemical Fe²⁺-activated peroxymonosulfate (PMS) oxidation process for removing 16 priority PAHs from real TDS was firstly investigated. The results showed that the removal efficiency of the ∑16PAHs in TDS was positively correlated to the concentration of Fe²⁺ released from sacrificial iron anode and the concentration of electroregenerated Fe²⁺ in the cathode by the reduction of Fe³⁺ within the applied voltage range of 3-7 V, but a higher voltage of 10 V did not lead to further improvement in ∑16PAHs removal due to the radical scavenging reaction resulted from the excessive accumulation of Fe²⁺. 64.7% and 16.1% of the ∑16PAHs were removed in the anodic and cathodic chamber under the optimum reaction conditions of 400 mg/g PMS/VSS, pH 3 and applied voltage 7 V, respectively. low-ring PAHs were preferentially degraded compared to high-ring PAHs. The O⋅Hplayed a major role while SO₄^⋅-had a minor role in PAHs degradation in TDS. The intracellular PAHs released from cracked sludge cells were found to undergo further degradation under free radical attack.

Fabrication of ZnAl-LDH mixed metal-oxide composites for photocatalytic degradation of 4-chlorophenol

In this work, two different types of ZnAl-layered double hydroxide (LDH) mixed metal-oxide composites (CeO₂ and SnO₂) were synthesized and applied for the photodegradation of 4-chlorophenol (4-CP) in wastewater. The fabricated CeO₂/ZnAl-LDH and SnO₂/ZnAl-LDH were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and theoretical density functional theory (DFT) calculations, suggesting that the band gaps of the synthesized hybrid composites were much lower than those of traditional ZnAl-LDH. In addition, the photocatalytic activity for 4-CP degradation and reaction kinetics were investigated to evaluate the catalytic behavior of the prepared composites. The results indicated that the photocatalytic process in this case followed a pseudo-first-order kinetic model, and SnO₂/ZnAl-LDH illustrated the optimum performance for 4-CP degradation with an efficiency of 95.2% due to its stability and recyclability. Additionally, the reaction mechanism of 4-CP photodegradation was studied over SnO₂/ZnAl-LDH; it presented that 4-CP could be oxidized by hydroxyl radicals, holes, and superoxide radicals, where hydroxyl radicals were identified as the dominant active species during the degradation process. Finally, decomposition intermediates were measured to deduce the reaction pathway of 4-CP, and three tentative pathways were proposed and discussed.

Regeneration and reuse of salt-tolerant zwitterionic polymer fluids by simple salt/water system

Highly-efficient separation of adsorbent and pollutant from chemical sludge is urgent for the recycled materials and chemical resources and minimization of sludge production in industry. Herein, an effortless and cost-efficient salt/water system is developed for efficient zwitterionic polymer/dye separation from chemical sludge. To achieve this aim, a novel salt-tolerant zwitterionic polymer (STZP) is synthesized through etherifying 2-chloro-4,6-bis(4-carboxyphenyl amino)-1,3,5-triazine onto corn starch. It is found that "all-surface-area" adsorption of dye can be achieved by in-situ sol-gel transition of STZP. Spent polymer fluid and solid-state dye can be easily regenerated and separated from sewage sludge by a simple salt/water system. At a high NaCl concentration (225 g/L), the separation factor between zwitterionic polymer and dye is up to 50.4, which is 50 times larger than that of salt-free solution. More importantly, the regenerated polymer fluids exhibit an outstanding reusability ability and can maintain over 92.8% decoloration efficiency for dyeing effluent after multiple adsorption-desorption cycles. This study thus provides a technically feasible and economically acceptable strategy for the recycling and reuse of polymer from hazardous textile sludge waste, greatly promising to achieve zero emissions toward conventional adsorption units.

Co-combustion, life-cycle circularity, and artificial intelligence-based multi-objective optimization of two plastics and textile dyeing sludge

Given the globally abundant availability of waste plastics and the negative environmental impacts of textile dyeing sludge (TDS), their co-combustion can effectively enhance the circular economies, energy recovery, and environmental pollution control. The (co-)combustion performances, gas emissions, and ashes of TDS and two plastics of polypropylene (PP) and polyethylene (PE) were quantified and characterized. The increased blend ratio of PP and PE improved the ignition, burnout, and comprehensive combustion indices. The two plastics interacted with TDS significantly in the range of 200-600 ℃. TDS pre-ignited the combustion of the plastics which in turn promoted the combustion of TDS. The co-combustions released more CO₂ but less CH₄, C-H, and CO as CO₂ was less persistent than the others in the atmosphere. The Ca-based minerals in the plastics enhanced S-fixation and reduced SO₂ emission. The activation energy of the co-combustion fell from 126.78 to 111.85 kJ/mol and 133.71-79.91 kJ/mol when the PE and PP additions rose from 10% to 50%, respectively. The co-combustion reaction mechanism was best described by the model of f(α) = (1-α)ⁿ. The reaction order was reduced with the additions of the plastics. The co-combustion operation interactions were optimized via an artificial neural network so as to jointly meet the multiple objectives of maximum energy production and minimum emissions.

Response of 2,4,6-trichlorophenol-reducing biocathode to burial depth in constructed wetland sediments

Biocathode systems could be used for in-situ bioremediation of chlorophenols (CPs) in constructed wetland (CW) sediments. However, little is known regarding whether or how cathode burial depths affect the dechlorination of CPs in sediments. Here, 2,4,6-trichlorophenol (2,4,6-TCP)-dechlorinating biocathode systems were constructed under a cathode potential of - 0.7 V (vs. a saturated calomel electrode, SCE) at three different cathode burial depths (5, 10, and 15 cm). The 2,4,6-TCP removal efficiency and average transformation rate with the biocathode increased by 21.46-36.86% and 14.63-34.88% compared to those in the non-electrode groups. Deeper cathode burial depths enhanced the 2,4,6-TCP dechlorination performance. Furthermore, the oxidation-reduction potential (ORP) of the sediment decreased with sediment depth and the applied potential created a more favorable redox environment for the enrichment of functional bacteria. Deeper cathode burial depths also promoted the selective enrichment of electro-active and dechlorinating bacteria (e.g., Bacillus and Dehalobacter, respectively). The biocathode thus served as the carrier, electron source, and regulator of functional bacteria to accelerate the transformation of 2,4,6-TCP (2,4,6-TCP → 2,4-dichlorophenol → 4-chlorophenol → phenol) in sediments. These results offer insights into the effects of cathode burial depth on 2,4,6-TCP dechlorination in sediments from a redox environment and microbial community structure standpoint.