Hand-pumps as reservoirs for microbial contamination of well water - PubMed (original) (raw)
Hand-pumps as reservoirs for microbial contamination of well water
Andrew S Ferguson et al. J Water Health. 2011 Dec.
Abstract
The retention and release of total coliforms and Escherichia coli was investigated in hand-pumps removed from tubewells tapping a faecally contaminated aquifer in Matlab, Bangladesh, and from a new hand-pump deliberately spiked with E. coli. All hand-pumps were connected to reservoirs of sterile water and flushed. Faecal coliforms were observed in the discharge from all three of the previously used hand-pumps, at concentrations comparable to levels measured in discharge when they were attached to the tubewells. During daily flushing of one of the previously used hand-pumps, the concentration of total coliforms in the discharge remained relatively constant (approximately 10³ MPN/100 mL). Concentrations of E. coli in the pump discharge declined over time, but E. coli was still detectable up to 29 days after the start of flushing. In the deliberately spiked hand-pump, E. coli was observed in the discharge over 125 days (t₅₀ = 8 days) and found to attach preferentially to elastomeric materials within the hand-pump. Attempts to disinfect both the village and new hand-pumps using shock chlorination were shown to be unsuccessful. These results demonstrate that hand-pumps can act as persistent reservoirs for microbial indicator bacteria. This could potentially influence drinking water quality and bias testing of water quality.
Figures
Figure 1
Tubewell no. 21602 (a) with original hand-pump attached and (b) replaced with a new hand-pump.
Figure 2
(a) Schematic of laboratory hand-pump experiment; and (b) location of swabs (1–7) taken from the internal surface of the new hand-pump.
Figure 3
Concentration of (a) total coliforms and (b) E. coli in discharge from the previously used hand-pumps prior to removal from their corresponding village tubewell, and following their attachment to reservoirs containing 50 L of filter-sterilized groundwater. Discharge from the reservoir-attached samples was collected on the 1st and 20th hand-pump stroke. Samples were also collected directly from the reservoirs after pumping. Error bars represent 95% confidence intervals.
Figure 4
Timeseries of (a) total coliforms and (b) E. coli concentrations within the pumped water discharge of the previously used hand-pump (no. 21602). Sterile artificial groundwater (50 L) was flushed daily through the hand-pump. Water samples were collected from the 1st (○) and 20th (□) strokes and directly from the reservoir after pumping (●). The reservoir was cleaned and refilled with sterile AGW after each sampling event.
Figure 5
Concentration of E. coli within the effluent of a purposely contaminated new hand-pump, before (days 0–56), during (day 56, 61 and 63) and after (days 63–125) shock chlorination. E. coli concentrations are given for the reservoir post flush (●) and from the hand-pump effluent following the 1st (○), 10th (Δ) and 20th (□) strokes. Concentrations of sodium hypochlorite used to shock chlorinate were 0.2 g/L (day 56), 0.4 g/L (day 61) and 1 g/L (day 63). Insert shows E. coli concentration (◆) in static batch microcosms.
Figure 6
Concentration of total coliforms in discharge from hand-pump no. 21602 on day 46 (before treatment), day 47 (after the first round of shock chlorination), day 50 (after the second round of shock chlorination), day 52 (after the third round of shock chlorination, combined with acid soaking and aggressive scrubbing) and day 53 (no treatment). Enumeration of total coliforms was determined following the 1st (▪) and 20th (□) strokes. Error bars represent 95% confidence intervals.
References
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