Understanding the effects of sludge characteristics on the biosorption of triclosan

Biodegradation of sulfadiazine in anaerobic co-digestion of swine manure and food waste

This study explored the feasibility of employing the AcoD process for the removal of antibiotics and examined the impact of antibiotics on system performance. Sulfadiazine (SDZ), a prevalent broad-spectrum sulfonamide antibiotic in veterinary medicine, was selected as the model compound. Results showed that with the presence of SDZ at a concentration of 450 mg/kg total solids, the cumulative methane yield demonstrated a substantial decline of 79.2 % compared to the control group. The specific removal rate of SDZ was 47.5 % at 450 mg SDZ/kg total solids, surpassing those observed in traditional mono-anaerobic treatment processes. The elimination of SDZ by the AcoD system was predominantly ascribed to biodegradation. Within the AcoD system, cytochrome P450 enzyme (CYP450) served as the crucial enzyme in the biodegradation of SDZ. From a molecular point of view, the main interaction sites of SDZ with CYP450 enzyme were located as Thr258, Glu257, Pro428, Ala254, and Val318. Six transformation products were identified in the biodegradation process. Community diversity revealed that the predominant genera, Syntrophomonadaceae, Acinetobacter, AUTHM297, and Anaerolineaceae, were enriched in the AcoD process, which probably contributed to SDZ removal. In summary, the AcoD system may possess sufficient robustness to transform SDZ antibiotic.

The potential of microplastics acting as vector for triclosan in aquatic environments

There is increased evidence of the co-occurrence of microplastics (MPs) with other co-pollutants in surface water globally, leading to ecological and environmental concerns. The risks and toxicity of co-occurring pollutants largely depend on the mechanisms controlling the activation of their various sources, their fate and transport in different environmental media. Due to their size-specific surface area, MPs in the environment can have a strong affinity for interactions with hydrophobic compounds and have a high sorption capacity for various emerging contaminants (ECs). ECs like the antibacterial and antifungal agent such as Triclosan (TCS) are persistent in the environment. Moreover, TCS in aquatic environments has a low solubility, and high octanol-water partitioning co-efficient which raises the possibility of TCS to interact with other environmental pollutants such as MPs. The interactions of TCS with MPs in the environment are controlled by a range of mechanism such as hydrogen bonding, hydrophobic interactions, π-π interactions as well as electrostatic interactions. The interacting behaviour of these driving forces needs to be fully understood to determine how the co-occurrence of TCS and MPs may lead to adverse effects on the biological functioning of aquatic ecosystems. Hence, here we conduct a systematic review of the current state-of-the-art and synthesize the available knowledge of how MPs can act as vectors for TCS in aquatic environments. This review reveals MP and TCS interactions in aquatic ecosystems, their individual and collective fate, and toxicological impacts on aquatic organisms, evidencing that MPs can act as potential vectors for transporting TCS across different trophic levels. This review also reveals critical limitations in the research of the combined toxicity and interactions of co-occurring MPs and TCS. Based on the rigorous review of the current knowledge base, we propose that multifactorious investigations along with long-terms monitoring are crucial to fully understand the impacts of co-occurring MPs and TCS in aquatic systems to underline future mitigation policies and management plans.

Exposure pattern of triclosan and tetracycline change their impacts on methanogenic digestion microbiomes

Triclosan (TCS) and tetracycline (TC) as common antibacterial agents are frequently detected in the influent of wastewater treatment plants. The TCS and TC exposure patterns may determine their impacts on wastewater treatment microbiomes, on which information remains unknown. In this study, the impacts of sequential exposure of TCS and TC on methanogenic digestion microbiomes in upflow anaerobic sludge blanket (UASB) reactors were analyzed and compared with that of the same microbiomes being simultaneously exposed to TCS and TC. Results indicated that the UASB reactor 2 (MD2) with sequential TCS-TC exposure consistently demonstrated higher chemical oxygen demand (COD) removal efficiency (94.7 %). In contrast, in the MD1 reactor, COD removal efficiency decreased from 94.4 % to 82.7 % upon simultaneous exposure to TCS and TC. Accordingly, a 1.8 times higher enrichment of total antibiotic resistance genes (ARGs) was observed in MD1 relative to MD2. Using a dissimilarity-overlap approach, the MD2 microbiome with sequential exposure was predominantly mediated by deterministic factors in their community assembly (largely contributed by abundant and intermediate biospheres), resulting in microbial interaction networks with higher average clustering coefficients and shorter average path lengths, compared to the MD1 microbiomes. Our results could support sustainable management of TCS and TC contamination in wastewater treatment plants.

H*ads dynamics engineering via bimetallic Pd-Cu@MXene catalyst for enhanced electrocatalytic hydrodechlorination

Electrocatalytic hydrodechlorination (EHDC) is a promising approach to safely remove halogenated emerging contaminants (HECs) pollutants. However, sluggish production dynamics of adsorbed atomic H (H*ads) limit the applicability of this green process. In this study, bimetallic Pd-Cu@MXene catalysts were synthesized to achieve highly efficient removal of HECs. The alloy electrode (Pd-Cu@MX/CC) exhibited better EHDC performance in comparison to Pd@MX/CC electrode, resulting in diclofenac degradation efficiency of 93.3 ± 0.1%. The characterization analysis revealed that the Pd0/PdII ratio decreased by forming bimetallic Pd-Cu alloy. Density functional theory calculations further demonstrated the electronic configuration modulation of the Pd-Cu@MXene catalysts, optimizing binging energies for H* and thereby facilitating H*ads production and tuning the reduction capability of H*ads. Noteably, the amounts and reduction potential of H*ads for Pd-Cu@MXene catalysts were 1.5 times higher and 0.37 eV lower than those observed for the mono Pd electrode. Hence, the introduction of Cu into the Pd catalyst optimized the dynamics of H*ads production, thereby conferring significant advantages to EHDC reactions. This augmentation was underscored by the successful application of the alloy catalysts supported by MXene in EHDC experiments involving other HECs, which represented a new paradigm for EHDC for efficient recalcitrant pollutant removal by H*ads.

Enhanced dewaterability and triclosan removal of waste activated sludge with iron-rich mineral-activated peroxymonosulfate

High water and pharmaceutical and care products (PPCPs) bounded in sludge flocs limit its utilization and disposal. The advanced oxidation process of perxymonosulfate (PMS) catalyzed by iron salts has been widely used in sludge conditioning. In this study, two iron-rich minerals pyrite and siderite were proposed to enhance sludge dewatering performance and remove the target contaminant of triclosan (TCS). The permanent release of Fe2+ in the activation of PMS made siderite more effective in enhancing sludge dewater with capillary suction time (CST) diminishing by 60.5 %, specific resistance to filtration (SRF) decreasing by 79.2 %, and bound water content (BWC) dropping from 37.1 % to 2.6 % at siderite/PMS dosages of 0.36/0.20 mmol/g-TSS after 20 min of pretreatment. Pyrite/PMS performed slightly inferior under the same conditions and the corresponding CST and SRF decreased by 51.5 % and 71.8 % while the BWC only declined to 17.8 %. Rheological characterization was employed to elucidate the changes in sludge dewatering performance, with siderite/PMS treated sludge showing a 48.3 % reduction in thixotropy, higher than 28.4 % of pyrite/PMS. Oscillation and creep tests further demonstrated the significantly weakened viscoelastic behavior of the sludge by siderite/PMS pretreatment. For TCS mineralization removal, siderite/PMS achieved a high removal efficiency of 43.9 %, in comparison with 39.9 % for pyrite/PMS. The reduction in the sludge solids phase contributed the most to the TCS removal. Free radical quenching assays and EPR spectroscopy showed that both siderite/PMS and pyrite/PMS produced SO4-·  and ·OH, with the latter acting as the major radicals. Besides, the dosage of free radicals generated from siderite/PMS exhibited a lower time-dependence, which also allowed it to outperform in destroying EPS matrix, neutralizing the negative Zeta potential of sludge flocs, and mineralizing macromolecular organic matter.

Pre-exposure of Triclosan compromise tetracycline-derived antibiotic resistance in methanogenic digestion microbiome

Triclosan (TCS) and tetracycline (TC) are commonly detected antibacterial agents in sewage and environment matrices. Nonetheless, the impact of sequential exposure to TCS and TC on the methanogenic digestion microbiome remains unknown. In this study, TCS was shown to reduce COD removal efficiency to 69.8%, but alleviated the inhibitive effect of consequent TC-amendment on the digestion microbiome. Interestingly, TCS pre-exposure resulted in abundance increase of acetotrophic Methanosaeta to 2.68%, being 2.91 folds higher than that without TCS amendment. Microbial network analyses showed that TCS pre-exposure caused microorganisms to establish a co-ecological relationship against TC disturbance. Further analyses of total antibiotic resistance genes (ARGs) showed the TCS-derived compromise of TC-induced ARGs enrichment in digestion microbiomes, e.g., 238.2% and 152.1% ARGs increase upon TC addition in digestion microbiomes without and with TCS pre-exposure, respectively. This study provides new insights into the impact of antibacterial agents on the methanogenic digestion microbiome.

Advantages of residual phenol in coal chemical wastewater as a co-metabolic substrate for naphthalene degradation by microbial electrolysis cell

The use of co-metabolic substrates is effective for polycyclic aromatic hydrocarbons (PAHs) removal, but the potential of the high phenol concentrations in coal chemical wastewater (CCW) as a co-metabolic substrate in microbial electrolysis cell (MEC) has been neglected. In this study, the efficacy of varying phenol concentrations in comparison to simple substrates for degrading naphthalene in MEC under comparable COD has been explored. Results showed that phenol as a co-metabolic substrate outperformed sodium acetate and glucose in facilitating naphthalene degradation efficiency at 50 mg-COD/L. The naphthalene removal efficiency from RP, RA, and RG was found to be 84.11 ± 0.44 %, 73.80 ± 0.27 % and 72.43 ± 0.34 %, respectively. Similarly, phenol not only enhanced microbial biomass more effectively, but also exhibited optimal COD metabolism capacity. The addition of phenol resulted in a stepwise reduction in the molecular weight of naphthalene, whereas sodium acetate and glucose led to more diverse degradation pathways. Some bacteria with the potential ability to degrade PAHs were detected in phenol-added MEC, including Alicycliphilus, Azospira, Stenotrophomonas, Pseudomonas, and Sedimentibacter. Besides, phenol enhanced the expression of ncrA and nmsA genes, leading to more efficient degradation of naphthalene, with ncrA responsible for mediating the reduction of the benzene ring in naphthalene and nmsA closely associated with the decarboxylation of naphthalene. This study provides guidance for the effective co-degradation of PAHs in CCW with MEC, demonstrating the effectiveness of using phenol as a co-substrate relative to simple substrates in the removal of naphthalene.

Atomic hydrogen-mediated enhanced electrocatalytic hydrodehalogenation on Pd@MXene electrodes

In this study, a Pd@MXene catalyst was synthesized to enhance the electrocatalytic hydrodehalogenation (ECH) of emerging halogenated organic pollutants (HOPs) by improving the dispersibility, catalytic activity, and stability of palladium (Pd). The average size of Pd nanoparticles (NPs) was reduced to 3.62 ± 0.34 nm with a more intensive peak of Pd (111), which facilitated atomic hydrogen (H*) production. The Pd@MX/CC electrode demonstrated superior ECH activity for diclofenac (DCF) degradation, with a reaction rate constant (kobs) 2.48 times higher than that of Pd/CC (without MXene). The satisfactory ECH performance of Pd@MX/CC remained consistent within a wide range of initial DCF concentrations (5-100 mg/L), and no significant ECH attenuation was observed even after up to 10 batches. Furthermore, the high activity of Pd@MX/CC was also observed in the ECH of other halogenated organic pollutants (levofloxacin, tetrabromobisphenol A, and diatrizoate). Density functional theory (DFT) calculations revealed that electronic configuration modulation of the Pd@MXene catalyst optimized binging energies to H* , DCF, and dechlorinated products, thereby enhancing the ECH efficiency of DCF.

Evaluation of the Respective Contribution of Anode and Cathode for Triclosan Degradation in a Bioelectrochemical System

In this work, the bioelectrochemical system (BES) is a feasible alternative for successfully degrading typical refractory emerging contaminant triclosan (TCS). A single-chamber BES reactor with an initial TCS concentration of 1 mg/L, an applied voltage of 0.8 V, and a solution buffered with 50 mM PBS degraded 81.4±0.2% of TCS, exhibiting TCS degradation efficiency improvement to 90.6±0.2% with a biocathode formed from a reversed bioanode. Both bioanode and biocathode were able to degrade TCS with comparable efficiencies of 80.8±4.9% and 87.3±0.4%, respectively. Dechlorination and hydrolysis were proposed as the TCS degradation pathway in the cathode chamber, and another hydroxylation pathway was exclusive in the anode chamber. Microbial community structure analysis indicated Propionibacteriaceae was the predominant member in all electrode biofilms, and the exoelectrogen Geobacter was enriched in anode biofilms. This study comprehensively revealed the feasibility of operating BES technology for TCS degradation.

Evaluation of the effect of biofilm formation on the reductive transformation of triclosan in cathode-modified electrolytic systems

The performance of electrochemical reduction is often enhanced by electrode modification techniques. However, there is a risk of microbial colonization on the electrode surface to form biofilms in the treatment of actual wastewater with modified electrodes. In this work, the effects of biofilm formation on modified electrodes with reduced graphene oxide (rGO), platinum/carbon (Pt/C), and carbon nanotube (CNT) were investigated in triclosan (TCS) degradation. With biofilm formation, the TCS degradation efficiencies of carbon cloth (CC), rGO@CC, Pt/C@CC, and CNT@CC decayed to 54.53 %, 59.77 %, 69.19 %, and 53.97 %, respectively, compared to the raw electrodes. Confocal laser scanning microscopy and microbial community analysis revealed that the difference in biofilm thickness and activity were the major influencing factors on the discrepant TCS degradation rather than the microbial community structure. The electrochemical performance tests showed that the biofilm formation increased the ohmic resistance by an order of magnitude in rGO@CC, Pt/C@CC, and CNT@CC, and the charge transfer resistance was increased by 2.45, 3.78, and 7.75 times, respectively. The dechlorination and hydrolysis governed the TCS degradation pathway in all electrolysis systems, and the toxicity of electrochemical reductive products was significantly decreased according to the Toxicity Estimation Software Tool analysis. This study presented a systematic assessment of the biofilm formation on modified electrodes in TCS reduction, and the undisputed experimental outcomes were obtained to enrich the knowledge of implementing modified electrodes for practical applications.