Natural inactivation of Escherichia coli in anoxic and reduced groundwater

Aims

Inactivation rates of E. coli in groundwater have most often been determined in aerobic and oxidized systems. This study examined E. coli inactivation rates in anaerobic and extremely reduced groundwater systems that have been identified as recharge zones.

Methods and Results

Groundwater from six artesian wells was diverted to above ground, flow through mesocosms that contained laboratory grown E. coli in diffusion chambers. All groundwater was anaerobic and extremely reduced (ORP < -300 mV). Cells were plated onto mTEC agar during 21 day incubation periods. All data fit a bi-phasic inactivation model, with > 95% of the E. coli population being inactivated < 11.0 hrs (mean k = 0.488± 0.188 h−1).

Conclusions

The groundwater geochemical conditions enhanced the inactivation of E. coli to rates approximately 21-fold greater than previously published inactivation rate in groundwater (mean k= 0.023 ± 0.030 h−1). Also, mTEC agar inhibits E. coli growth following exposure to anaerobic and reduced groundwater.

Significance and Impact of the Study

Aquifer recharge zones with geochemical characteristics observed in this study complement above ground engineered processes (e.g., filtration, disinfection), while increasing the overall indicator microorganism log-reduction rate of a facility.