Electro-assisted autohydrogenotrophic reduction of perchlorate and microbial community in a dual-chamber biofilm-electrode reactor

Electrochemical reductive removal of trichloroacetic acids by a three-dimensional binderless carbon nanotubes/ CoP/Co foam electrode: Performance and mechanism

Numerous chlorinated disinfection by-products (DBPs) are produced during the chlorination disinfection of water. Among them, chloroacetic acids (CAAs) are of great concern due to their potential human carcinogenicity. In this study, effective electrocatalytic dechlorination of trichloroacetic acids (TCAA), a typical CAAs, was achieved in the electrochemical system with the three-dimensional (3D) self-supported CoP on cobalt foam modified by carbon nanotubes (CNT/CoP/CF) as the cathode. At a 10 mA cm-2 current density, 74.5% of TCAA (500 μg L-1) was converted into AA within 100 min. In-situ growth of CoP increased the effective electrochemical surface area of the electrode. Electrodeposited CNT promoted electron transfer from the electrode surface to TCAA. Therefore, the production of surface-adsorbed atomic hydrogen (H*) on CNT/CoP/CF was improved, further resulting in excellent electrochemical dechlorination of TCAA. The dechlorination pathway of TCAA proceeded into acetic acids via direct electronic transfer and H*-mediated reduction on CNT/CoP/CF electrode. Additionally, the electroreduction efficiency of CNT/CoP/CF for TCAA exceeded 81.22% even after 20 cycles. The highly efficient TCAA reduction performance (96.57%) in actual water revealed the potential applicability of CNT/CoP/CF in the complex water matrix. This study demonstrated that the CNT/CoP/CF is a promising non-noble metal cathode to remove chlorinated DBPs in practice.

Performance and mechanism of sacrificed iron anode coupled with constructed wetlands (E-Fe) for simultaneous nitrogen and phosphorus removal

Three anodic biofilm electrode coupled CWs (BECWs) with graphite (E-C), aluminum (E-Al), and iron (E-Fe), respectively, and a control system (CK) were constructed to evaluate the removal performance of N and P in the secondary effluent of wastewater treatment plants (WWTPs) under different hydraulic retention time (HRT), electrified time (ET), and current density (CD). Microbial communities, and different P speciation, were analyzed to reveal the potential removal pathways and mechanism of N and P in BECWs. Results showed that the optimal average TN and TP removal rates of CK (34.10% and 55.66%), E-C (66.77% and 71.33%), E-Al (63.46% and 84.93%), and E-Fe (74.93% and 91.22%) were obtained under the optimum conditions (HRT 10 h, ET 4 h, CD 0.13 mA/cm²), which demonstrated that the biofilm electrode could significantly improve N and P removal. Microbial community analysis showed that E-Fe owned the highest abundance of chemotrophic Fe(II) (Dechloromonas) and hydrogen autotrophic denitrifying bacteria (Hydrogenophaga). N was mainly removed by hydrogen and iron autotrophic denitrification in E-Fe. Moreover, the highest TP removal rate of E-Fe was attributed to the iron ion formed on the anode, causing co-precipitation of Fe(II) or Fe(III) with PO₄^3--P. The Fe released from the anode acted as carriers for electron transport and accelerated the efficiency of biological and chemical reactions to enhance the simultaneous removal of N and P. Thus, BECWs provide a new perspective for the treatment of the secondary effluent from WWTPs.

Deciphering the effects of antibiotics on nitrogen removal and bacterial communities of autotrophic denitrification systems in a three-dimensional biofilm electrode reactor

In this study, three-dimensional biofilm electrode reactors (3D-BERs) were constructed, and the effects of metronidazole (MNZ) on the nitrogen removal performance and bacterial communities of autotrophic denitrification systems were evaluated. The results showed that nitrogen removal decreased slightly as the MNZ concentration increased. Specifically, nitrate-nitrogen removal efficiency decreased from 97.98% to 89.39%, 86.93%, 82.64%, and 82.77% within 12 h after the addition of 1, 3, 5, and 10 mg/L MNZ, respectively. The 3D-BERs showed excellent MNZ degradation ability, especially at a concentration of 10 mg/L. The MNZ removal efficiency could be as high as 94.38% within 6 h, and the average removal rate increased as the MNZ concentration increased. High-throughput sequencing results showed significant changes in the bacterial community under different MNZ concentrations. As the antibiotic concentration increased, the relative abundances of Hydrogenophaga and Silanimonas increased, from only 0.09% and 0.01% without antibiotics to 3.55% and 2.35%, respectively, at an antibiotic concentration of 10 mg/L. Changes in antibiotic concentration altered the abundances of genes involved in nitrogen metabolism. Redundancy analysis showed that MNZ removal efficiency was positively correlated with SBR1031, SC-I-84, Hydrogenophaga, Silanimonas and Denitratesoma, whereas the removal efficiencies of nitrate-nitrogen and total nitrogen were negatively correlated with these genera. The results of this study provide a theoretical basis for studying the toxic effects of antibiotics on the denitrification process and also provide guidance for the control of antibiotics and nitrogen pollution in ecosystems.

Achieving high-performance electrocatalytic reduction of nitrate by N-rich carbon-encapsulated Ni-Cu bimetallic nanoparticles supported nickel foam electrode

The cathode with low-energy consumption and long-term stability is pivotal to achieve the conversion of nitrate (NO₃^-) to nitrogen (N₂) by electrocatalytic denitrification. Herein, a binder-free electrode was synthesized by directly immobilizing N-doped graphitized carbon layer-encapsulated NiCu bimetallic nanoparticles on nickel foam (NF) (NiCu@N-C/NF) and served as the cathode for electrocatalytic NO₃^- reduction. Morphological characterization indicated that Ni and Cu nanoparticles were encapsulated by the N-doped graphitized carbon layer and well-dispersed on the surface of NF. Compared with monometallic composite cathode (Cu@N-C/NF and Ni@N-C/NF), NiCu@N-C/NF exhibited better NO₃^- removal performance (98.63 %) and lower energy consumption (0.007 kW·h mmol^-1), which should be attributed to its strong adsorption ability to NO₃^- and excellent electron transfer property. Meanwhile, its electrocatalytic performance could be maintained in wide initial NO₃^- concentration (1.79-7.14 mM) and solution pH (3-11). With the assistance of electrochlorination, the N₂ selectivity of electrochemical system was up to 99.89 % in the presence of 0.028 M Cl^-. More importantly, NiCu@N-C/NF electrode displayed an ultra-high stability during ten recycling experiments. This study indicated that the binderless composite cathode NiCu@N-C/NF had great potential in electrocatalytic NO₃^- removal from wastewater.