The role of bacteria in well clogging

The effect of ochreous sludge from blocked irrigation bores on the oxidation rate of soluble Fe(II) was studied. Solutions of Fe(II) at an initial concentrations of 12–15 ppm were held at 19°C under an oxygen partial pressure of ca 1.4% and the decline in Fe(II) concentration observed. Solutions were buffered with 2-(N-morpholino) ethanesulfonic acid (MES) at pH values of 5.8, 6.0, 6.3 and 6.5. Sterile flasks showed agreement with the expected 1st order behaviour (with respect to [Fe(II)]) while flasks inoculated with ochreous sludge deviated significantly from this pattern. Rates of Fe(II) oxidation were significantly enhanced in the inoculated flasks with the greatest increase observed at pH 5.8.