Bioelectrochemical catabolism of triclocarban through the cascade acclimation of triclocarban-hydrolyzing and chloroanilines-oxidizing microbial communities

Mitigation of Triclocarban Inhibition in Microbial Electrolysis Cell-Assisted Anaerobic Digestion

Triclocarban (TCC), as a widely used antimicrobial agent, is accumulated in waste activated sludge at a high level and inhibits the subsequent anaerobic digestion of sludge. This study, for the first time, investigated the effectiveness of microbial electrolysis cell-assisted anaerobic digestion (MEC-AD) in mitigating the inhibition of TCC to methane production. Experimental results showed that 20 mg/L TCC inhibited sludge disintegration, hydrolysis, acidogenesis, and methanogenesis processes and finally reduced methane production from traditional sludge anaerobic digestion by 19.1%. Molecular docking revealed the potential inactivation of binding of TCC to key enzymes in these processes. However, MEC-AD with 0.6 and 0.8 V external voltages achieved much higher methane production and controlled the TCC inhibition to less than 5.8%. TCC in the MEC-AD systems was adsorbed by humic substances and degraded to dichlorocarbanilide, leading to a certain detoxification effect. Methanogenic activities were increased in MEC-AD systems, accompanied by complete VFA consumption. Moreover, the applied voltage promoted cell apoptosis and sludge disintegration to release biodegradable organics. Metagenomic analysis revealed that the applied voltage increased the resistance of electrode biofilms to TCC by enriching functional microorganisms (syntrophic VFA-oxidizing and electroactive bacteria and hydrogenotrophic methanogens), acidification and methanogenesis pathways, multidrug efflux pumps, and SOS response.

Enhanced thyroxine removal from micro-polluted drinking water resources in a bio-electrochemical reactor amended with TiO2@GAC particles: Efficiency, mechanism and energy consumption

A three-dimensional bioelectrochemical system (3D-BES) with both electrocatalytic and biodegradation functions was designed and developed to enhance iodine-containing hormone removal from micro-polluted oligotrophic drinking water sources and to reduce energy consumption. Thyroxine (T4) removal efficiency was 99.0% in the 3D-BES amendment with TiO2@GAC as the particle electrodes, which was 20.5% higher than the total efficiency of single biodegradation (28.7%) plus electrochemical decomposition (49.8%). The high T4 removal efficiency was a result of biochemical synergistic degradation, enhancement of electron transfer and utilization, enrichment of functional microorganisms, and the expression of dehalogenation functional genes. The electron transfer was increased by 1.63 times in 3D-BES compared to the 2D-BES, which contributed to: (i) ∼17.8% enhancement of dehalogenation, (ii) 2.35 times enhancement of the attenuation rate, and (iii) 60% reduction in energy consumption. Moreover, the aggregation of microorganisms and the hydrophobic T4 onto TiO2@GAC shortened the transfer distance of matter and energy, which induced the degradation steps to be shortened and the toxic decay to be accelerated from T4 and its metabolites. These comprehensive functions also enhanced the 31.8% ATPase activity, 7.3% abundance of the functional reductive dehalogenation genera, and 52.3% dehalogenation genes expression for Pseudomonas, Ancylobacter, and Dehalogenimonas, which contributed to an increase in T4 removal. This work provides an environmental-friendly biochemical synergistic method for the detoxification of T4 polluted water.

Effects of different cathodic potentials on performance, microbial community structure and function for bioelectrochemical-stimulated dechlorination of 2,4,6-trichlorophenol in sediments

Bioelectrochemical systems with biocathodes constitute a promising means to enhance the biological dechlorination of 2,4,6-trichlorophenol (2,4,6-TCP) in constructed wetland (CW) sediments. However, the effect of different cathodic potentials on the structure and function of 2,4,6-TCP-reducing biocathode communities in CW sediments is largely unknown. Here, we evaluated the performance and microbial community structure of 2,4,6-TCP-reducing biocathode systems at different cathodic potentials (- 0.5, - 0.7, - 0.9, and - 1.1 V vs. saturated calomel electrode). The dechlorination efficiency of 2,4,6-TCP with the biocathode relatively increased by 16.02%-33.17% compared to that in the open circuit. The highest 2,4,6-TCP dechlorination efficiency (92.34 ± 0.86%) was observed at - 0.7 V in sediment, which may be due to the highest abundance of functional genera (e.g., Pseudomonas, Spirochaeta) at - 0.7 V. Metagenomic analysis provided new insights into the metabolic potential of microorganisms in CW sediments and suggested possible 2,4,6-TCP conversion pathways in sediments. 2,4,6-TCP was gradually dechlorinated to form 4-chlorophenol, followed by a ring-opening step via the activities of chlorophenol reductive dehalogenase and oxygenase (e.g., cprA, tfdB). Interestingly, micro-electrical stimulation enhanced the expression of chlorophenol reductive dehalogenase (cprA). Therefore, our findings at the molecular and gene expression levels provide insights into the effects of different cathodic potentials on the performance and community structure of 2,4,6-TCP-reducing biocathode systems in CW sediments.

Fate, toxicity and effect of triclocarban on the microbial community in wastewater treatment systems

Triclocarban (TCC), one of the typical antimicrobial agents, is a contaminant of emerging concern commonly found in high concentration in water environments. However, the fate and toxicity of TCC in wastewater treatment systems remain poorly understood. Here, we investigated how TCC impacts chemical oxygen demand and inorganic nitrogen transformation in a hydrolytic anaerobic-anoxic/oxic process. In the anaerobic section, the transformation of TCC was dominated by reductive dechlorination and supplemented by two amid bonds hydrolysis. In the anoxic and oxic sections, the hydrolysis of amid bonds dominated. The toxicity was reduced after the treatment (IC₅₀ from 0.09 to 0.54). TCC inhibited NH₄⁺-N removal in the anaerobic section and led to the NO₃^--N accumulation (2.84-4.13 mg/L) after treatment, with the abundance of N-removal bacteria decreased by 6%. Furthermore, the original ecological niche was gradually replaced by TCC-resistant/degradative bacteria, formating new microbial modules to resist the TCC stress. Importantly, fourteen genera including Methanosaeta, Longilinea, Dokdonella and Mycobacterium as potential bioindicators warning TCC and its intermediates were proposed. Overall, this study provides new insights into the fate of TCC in biological wastewater treatment systems and suggests a great importance for TCC control to ensure the health and resilience of ecosystems.

Catalyzing urea hydrolysis using two-step microbial-induced carbonate precipitation for copper immobilization: Perspective of pH regulation

Microbial induced carbonate precipitation (MICP) has recently applied to immobilize heavy metals toward preventing their threats to public health and sustainable development of surrounding environments. However, for copper metallurgy activities higher copper ion concentrations cause the ureolytic bacteria to lose their activity, leading to some difficulty in forming carbonate precipitation for copper immobilization (referred to also as “biomineralization”). A series test tube experiments were conducted in the present work to investigate the effects of bacterial inoculation and pH conditions on the copper immobilization efficiency. The numerical simulations mainly aimed to compare with the experimental results to verify its applicability. The copper immobilization efficiency was attained through azurite precipitation under pH in a 4–6 range, while due to Cu²⁺ migration and diffusion, it reduced to zero under pH below 4. In case pH fell within a 7–9 range, the immobilization efficiency was attained via malachite precipitation. The copper-ammonia complexes formation reduced the immobilization efficiency to zero. The reductions were attributed either to the low degree of urea hydrolysis or to inappropriate pH conditions. The findings shed light on the necessity of securing the urease activity and modifying pH conditions using the two-step biomineralization approach while applying the MICP technology to remedy copper-rich water bodies.