Natural inactivation of Escherichia coli in anaerobic and reduced groundwater

J.T. Lisle

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. 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) ). 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. 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. This article is protected by copyright. All rights reserved.