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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.
Highlights
Shallow groundwater wells, are the main source of drinking water in many rural and peri-urban communities (Schmoll et al, 2006)
The first objective of this work was to observe a change in voltage/current production after the addition of faecal pollution on different Microbial fuel cells (MFC) concepts embedded in a groundwater system
DO levels were lower after contamination, they remained above 2 mg/L indicating that oxygen was still available to be reduced at the cathode of MFCs
Summary
Shallow groundwater wells, are the main source of drinking water in many rural and peri-urban communities (Schmoll et al, 2006). The quantity and variety of shallow wells located in such communities make them more readily accessible than private or government operated deep boreholes, but shallow wells are more susceptible to faecal contamination, which is often due to leaching pit latrines (Schmoll et al, 2006) For this reason, online monitoring (S.B. Velasquez-Orta). Other methods available for detecting microbiological quality of water; i.e. faecal sterols, microbial source tracking, and other indicators such as Clostridia, or bacteriophages, present accuracy challenges (Murtaugh and Bunch, 1967; Tyagi et al, 2006) This is due to the high susceptibility of the coliforms to chemical disinfection and failing to correlate with other microorganisms that can cause diseases such as parasites, protozoan, and enteric viruses (Tyagi et al, 2006). The development of affordable continuous measurement tools providing early warnings for significant pollution events and supplementary in-situ information on the quality of groundwater at low cost and low maintenance, by creating a signal from the water pollution itself, without external chemical or power input, is extremely challenging and of paramount importance
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