Evaluation of electrode separators and the external resistance in electrochemically assisted constructed wetlands.

A proton exchange membrane increases the electrical performance of a microbial fuel cell (MFC). New inexpensive materials should be sought, especially in a constructed wetland microbial fuel cell (CW-MFC). Here, in a laboratory-scale system of five CW-MFCs, wet clay, wet earth or mud, and non-woven cloth were used as inexpensive separators with long-term stability. The five CW-MFCs were planted with Typha latifolia, fed with synthetic wastewater, and packed with natural porous material. Graphite felt was used as electrodes and the experimental system had a hydraulic residence time of 3 days, operating under shade and natural conditions of temperature and light. Electrodes were connected to current collectors (copper wire) and to an external resistance, with a change every 20 days, starting in open-circuit and following with 20000, 18000, 15000, 10000, 5600, 1000, 560, and 10 Ω. These laboratory-scale CW-MFCs reduced concentrations of nitrates, ammonium ion, and sulfates without inhibiting electricity production. Microbiological analyses indicated that anaerobic, facultative, aerobic, and denitrifying bacteria may have caused these reductions. The reactor with the live plant and with the wet earth or mud separator achieved the highest production of electricity (22.6 mW/m2), and may be worth further attention.

Rapid electrochemical recognition of trimethoprim in human urine samples using new modified electrodes (CPE/Ag/Au NPs) analysing tunable electrode properties: experimental and theoretical studies.

Pharmaceutical effluents are a serious environmental issue, which require to be treated by a suitable technique; thus, the electrochemical process is actively considered as a viable method for the treatment. In this work, new carbon paste electrodes (CPEs) were fabricated by compressing gold and silver nanoparticles (NPs), namely, CPE/Ag NPs, CPE/Au NPs, and CPE/Ag/Au NPs and then completely characterized by different analytical methods. The performance of the electrodes was studied after determining their surface area (×10-6 cm2) as 4.17, 5.05, 5.27, and 5.12, producing high anodic currents for K4[Fe(CN)6] compared to the commercial electrode. This agrees with the results of impedance study, where the electron transfer rate constants (kapp, ×10-3 cm s-1) were determined to be 28.7, 42.6, 41.0, and 101.4 for CPE, CPE/Ag NPs, CPE/Au NPs, and CPE/Ag/Au NPs, respectively, through the Bode plot-phase shifts. This is consistent with the charge transfer resistance (RCT, Ω), resulting as 171 for CPE/Ag/Au NPs < 395 for CPE/Ag NPs < 427 for CPE/Au NPs and < 742 for CPE. Therefore, these electrodes were employed to detect trimethoprim (TMP) since metallic NPs contribute good crystallinity, stability, conduciveness, and surface plasmon resonance to the CPE, convalescing the sensitivity; comprehensively, they were applied for its detection in real water and human urine samples, and the limit of detection (LOD) was as low as 0.026, 0.032, and 0.026 µmol L-1 for CPE/Ag NPs, CPE/Au NPs, and CPE/Ag/Au NPs, respectively. In contrast, unmodified CPE was unable to detect TMP due to the lack of efficiency. The developed technique shows excellent electrochemical recovery of 92.3 and 97.1% in the urine sample. Density functional theory (DFT) was used to explain the impact of the metallic center in graphite through density of states (DOS).