Natural inactivation of MS2, poliovirus type 1 and Cryptosporidium parvum in an anaerobic and reduced aquifer

Abstract

Aims:The study of microbial inactivation rates in aquifer systems has most often been determined in aerobic and oxidized systems. This study examined the inactivation (i.e. loss of infectivity) of MS2, poliovirus type 1 (PV1) and Cryptosporidium parvum in an anaerobic and reduced groundwater system that has been identified as storage zones for aquifer storage and recovery (ASR) facilities.Methods and Results: Anaerobic and reduced (ORP < − 250 mV) groundwater from an artesian well was diverted to an above-ground, flow-through mesocosm that contained diffusion chambers filled with MS2, PV1 or Cryptosporidium parvum. The respective infectivity assays were performed on microorganisms recovered from the diffusion chambers during 30-to 58-day experiments. The net reduction in infectivity was 5.73 log 10 over 30 days for MS2, 5.00 log 10 over 58 days for PV1 and 4.07 log 10 over 37 days for C. parvum. The best fit inactivation model for PV1 was the loglinear model and the Weibull model for MS2 and C. parvum, with respective inactivation rates (95% confidence interval) of 0.19 (0.17-0.21) log 10 day −1 , 0.31 (0.19-0.89) log 10 day −1 and 0.20 (0.14-0.37) log 10 day −1 . Conclusions:The groundwater geochemical conditions in this aquifer enhanced the inactivation of MS2, PV1, and C. parvum at rates approximately 2.0-5.3-fold, 1.2-17.0-fold, and 4.5-5.6-fold greater, respectively, than those from published studies that used diffusion chambers in aerobic-to-anoxic groundwater systems, with positive redox potentials. Significance and Impact of theStudy: Geochemical conditions like those in the aquifer zone in this study can naturally and significantly reduce concentrations of microbial indicators and pathogens of human health concern in injected surface water. Appropriate storage times for injected surface water could complement aboveground engineered processes for microorganism removal and inactivation (e.g. filtration, disinfection) by naturally increasing overall microorganism log-inactivation rates of ASR facilities.

Informing ASR Treatment Practices in a Florida Aquifer through a Human Health Risk Approach

“…All inactivation rate data were generated from experiments conducted in two nonpotable aquifer zones within the Floridan Aquifer System in central-to-south Florida: Upper Floridan (UF) and Avon Park Permeable Zone (APPZ) [15,16,22]. The depth of each aquifer zone from which the groundwater was accessed and associated information for each of the sample sites are provided in Table 1 and Figure 1.…”

“…The water quality data summaries from the groundwater wells accessed during the inactivation studies are listed in Table 2. All groundwater zones are anaerobic and contain no NO 3 or NO 2 [15,16,22]. Previous microbial inactivation studies in the aquifer zones described in Sections 2.1.1 and 2.1.2 determined that the following microorganisms-E. coli, Pseudomonas aeruginosa (P. aeruginosa), poliovirus type 1 (PV1) and Cryptosporidium parvum (C. parvum)followed bi-phasic (E. coli and P. aeruginosa), log-linear (PV1) and Weibull (C. parvum) inactivation models [15,16].…”

“…The inactivation model parameters are summarized in Table 3. Descriptions of study design, microorganism enumeration and statistical analyses are not reported in this study and can be found in the published literature [15,16,22].…”

“…In fact, fecal coliforms, Escherichia coli (E. coli), bacteriophages (e.g., MS2) and eukaryotic viruses (e.g., adenovirus, rotavirus) and encysted protozoans (e.g., Cryptosporidium sp., Giardia sp.) have been shown to be inactivated during the storage of recharged surface water in aquifer zones [10][11][12][13][14], including the Floridan Aquifer [15,16].…”

“…This approach can inform policy regarding the value of pathogen inactivation during storage cycles at ASR facilities in the context of meeting regulatory standards and the critical need to incorporate environmental conditions into treatment trains, regulatory criteria and decision making. This study utilizes previously published pathogen inactivation rates from studies in the Upper Floridan (UF) and Avon Park Permeable Zone (APPZ) zones within the Floridan Aquifer System located in centralto-south Florida [15,16] to inform pathogen inactivation and human health risks over time in the respective ASR storage zones.…”