Microbial fuel cells for inexpensive continuous in-situ monitoring of groundwater quality

Abstract

Online monitoring of groundwater quality in shallow wells to detect faecal or organic pollution could dramatically improve understanding of health risks in unplanned peri-urban settlements. Microbial fuel cells (MFC) are devices able to generate electricity from the organic matter content in faecal pollution making them suitable as biosensors. In this work, we evaluate the suitability of four microbial fuel cell systems placed in different regions of a groundwater well for the low-cost monitoring of a faecal pollution event. Concepts created include the use of a sediment/bulk liquid MFC (SED/BL), a sediment/sediment MFC (SED/SED), a bulk liquid/air MFC (BL/Air), and a bulk liquid/bulk liquid MFC (BL/BL). MFC electrodes assembly aimed to use inexpensive, durable, materials, which would produce a signal after a contamination event without external energy or chemical inputs. All MFC configurations were responsive to a contamination event, however SED/SED and BL/Air MFC concepts failed to deliver a reproducible output within the tested period of time. BL/BL MFC and SED/BL MFCs presented an increase in the average current after contamination from -0.75 ± 0.35 μA to -0.66 ± 0.41 μA, and 0.07 ± 0.2 mA to 0.11 ± 0.03 mA, respectively. Currents produced by the SED/BL MFC (SMFC) were considerably higher than for the BL/BL MFCs, making them more responsive, readable and graphically visible. A factorial design of experiments (DOE) was applied to evaluate which environmental and design factors had the greatest effect on current response in a contamination event. Within the ranges of variables tested, salinity, temperature and external resistance, only temperature presented a statistically significant effect (p = 0.045). This showed that the biosensor response would be sensitive to fluctuations in temperature but not to changes in salinity, or external resistances produced from placing electrodes at different distances within a groundwater well.

Real-time detection of faecally contaminated drinking water with tryptophan-like fluorescence: defining threshold values

“…Numerous researchers have already proposed alternative methods (Berg and Fiksdal 1988, Chen et al 2015, Frahm and Obst 2003, Guion et al 2008, Gunda et al 2014, Harwood et al 2014, Lopez-Roldan et al 2013, Maheux et al 2011, Radke and Alocilja 2005, Rinttilä et al 2004, Rompré et al 2002, Velasquez-Orta et al 2017), yet this has not led to a single successful commercial product. Tryptophan-like fluorescence (TLF) is a component of UV-fluorescent dissolved organic matter at excitation-emission wavelengths of 280 nm and 360 nm and is a viable potential alternative.…”

Opportunities for groundwater microbial electro‐remediation

“…Last but not least, small MET systems can also be used as biosensors to monitor the microbial activity in the aquifer (Williams et al ., ; Wardman et al ., ) or to evaluate its chemical state (Feng et al ., ; Webster et al ., ; Velasquez‐Orta et al ., ).…”

<em>In situ</em> Groundwater Treatment with Bioelectrochemical Systems (BES): Critical Review and Future Perspectives

“…Velasquez-Orta and co-workers (2017) designed an MFC-based biosensor for the online monitoring of fecal and organic pollution in shallow groundwater wells, obtaining responsive increases in the current produced; the system was sensitive to temperature fluctuations but not to changes in salinity or modifications of the external resistance (and thus to longer wiring for the connections of the electrodes). Field tests highlighted the influence of water level oscillations in the wells causing air exposition at the cathode (Velasquez-Orta et al, 2017). Organic matter presence in an aquifer undergoing bioremediation was ascertained by the increase in current density in a BES-based biosensor; current quickly dropped when organic matter presence was discontinued, suggesting that the system was able to monitor subsurface microbial activity during in situ bioremediation (Williams et al, 2010).…”