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The traditional microbial fuel cell (MFC) sensor with bioanode as sensing element delivers limited sensitivity to toxicity monitoring, restricted application to only anaerobic and organic rich water body, and increased potential fault warning to the combined shock of organic matter/toxicity. In this study, the biocathode for oxygen reduction reaction was employed for the first time as the sensing element in MFC sensor for toxicity monitoring. The results shown that the sensitivity of MFC sensor with biocathode sensing element (7.4±2.0 to 67.5±4.0 mA% −1 cm −2 ) was much greater than that showed by bioanode sensing element (3.4±1.5 to 5.5±0.7 mA% −1 cm −2 ). The biocathode sensing element achieved the lowest detection limit reported to date using MFC sensor for formaldehyde detection (0.0005%), while the bioanode was more applicable for higher concentration (>0.0025%). There was a quicker response of biocathode sensing element with the increase of conductivity and dissolved oxygen (DO). The biocathode sensing element made the MFC sensor directly applied to clean water body monitoring, e.g., drinking water and reclaimed water, without the amending of background organic matter, and it also decreased the warning failure when challenged by a combined shock of organic matter/toxicity. [ABSTRACT FROM AUTHOR]

As serious water ecological pollution caused by toxicant leakage occurs frequently, early-warning for toxicity presented in water environment attracts increasing attentions as it saves time to retain water safety and human health. Electrochemically active biofilm (EAB) sensor is a promising device for in situ real-time water toxicity early-warning. To improve the sensitivity of EAB sensor particularly for low-concentration toxicity warning, this study employed titanium mesh (TiM) as the anode to construct an EAB sensor. Compared to traditional EAB sensor with carbon felt (CF) anode, the sensitivity of the TiM sensor was increased up to 37.4 times. The effects of mesh size (TiM50, TiM100, TiM150) and operation mode (flow-by and flow-through) on the sensitivity of TiM sensors were further investigated. Results showed the sensor with TiM100 anode had the highest inhibition rate (IR) in flow-by mode, attributed to low charge transfer resistance (R ct) and fast mass transfer. Flow-through operation could further enhance TiM100 sensor's sensitivity from flow-by operation and succeeded to signal as low as 0.0025% formaldehyde, the lowest so far tested in EAB sensor with sensing anode. Multiple toxicity shocks on flow-through TiM100 sensor revealed its good recoverability towards all tested formaldehyde concentration from 0.01% to 0.0025%, during which electrochemical activity degradation and biomass accumulation partially impaired the repeatability. This work highlights the great improvement of EAB sensors by utilizing titanium mesh as EAB carrier and provides a reference for the practical application of metallic materials for EAB sensors. [ABSTRACT FROM AUTHOR]