Abstract
The growing use of herbicides in agriculture poses increasing concerns on the pollution of water systems worldwide. To be able to assess the presence of these compounds in waters and limit their impact on human health and ecosystems, the development of effective in-situ monitoring tools is key. Yet, many existing sensing technologies are not suitable for in-situ and remote applications, due to challenges in portability, durability, cost and power requirements. In this study, we explore for the first time the use of an algal-assisted cathode in a photosynthetic microbial fuel cell (p-MFC) as a self-powered dissolved oxygen probe for herbicides detection in water. The cathode is enriched with the alga Scenedesmus obliquus and two different electrode materials are tested, graphite felt and indium tin oxide, which mainly differ in porosity, surface roughness and transparency. Despite the much larger specific surface area of graphite felt compared to indium tin oxide, the current generated under light was only 10 times larger (109 ± 2µA vs. 10.5 ± 0.6 µA) and 8 times larger in the dark (37 ± 5 µA vs. 4.2 ± 0.6 µA). By generating a current output that correlates with the dissolved oxygen in the catholyte, the resulting p-MFCs could detect the EU legal atrazine concentration limit of 0.1 µg L-1. The use of graphite felt led to shorter response times and better sensitivity, as a result of the greater current baseline. In both cases, the current baseline was recovered after exposure of the sensor to frequent toxic events, thus showing the resilience of the cathodic biofilm and the potential of the p-MFCs for early warnings of herbicides pollution in water.
Highlights
Agricultural pollution is one of the major causes of degradation of water systems worldwide
This study explores the use of a photosynthetic cathode as the sensing element in a photo microbial fuel cell (p-Microbial Fuel Cell (MFC)) sensor for atrazine in water via the detection of dissolved oxygen changes in the catholyte
To evaluate the effect that the electrode porosity and transparency have on the sensing performance, two electrode materials were tested at the cathode: graphite felt (GF), used in pMFCGF; and Indium Tin Oxide coated on Polyethylene Terephthalate (ITO/PET), used in p-MFCITO
Summary
Agricultural pollution is one of the major causes of degradation of water systems worldwide. Population growth, and the consequent increase in food demand, has led to an intensified use of pesticides and chemical fertilizers in agriculture that contaminate waters, posing serious risks to aquatic ecosystems and human health (FAO). GRAPHICAL ABSTRACT | The photosynthetic MFC (p-MFC) presented in this work could target either point source contamination (A) or help monitoring the quality of influents in algal raceway ponds (B). The presence of a bioactive compound in the catholyte, such as atrazine, will cause a drop in the DO, which is translated into a change in the output signal generated by the p-MFC (D). The p-MFC acts as a self-powered early warning tool
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