Microbial risk assessment for recreational use of the Chicago area waterway system.

A microbial risk assessment was conducted to estimate the human health risks from incidental contact recreational activities such as canoeing, boating and fishing in the Chicago Area Waterway System (CAWS) receiving secondary treated, but non-disinfected, effluent from three municipal water reclamation plants. Actual concentrations of the pathogens (pathogenic E. coli [estimated], Giardia, Cryptosporidium, adenovirus, norovirus, enteric virus) detected from the waterway field data collection at locations upstream and downstream of the effluent outfall during dry and wet weather conditions within the recreation season were included in the risk assessment. The results under the current treatment scheme with no disinfection indicated that the total expected gastrointestinal illness (GI) rate per 1000 incidental contact recreational exposure events during combined weather (dry and wet) conditions ranged from 0.10 to 2.78 in the CAWS, which is below the eight illnesses per 1000 swimmers considered tolerable by the United States Environmental Protection Agency. Wet weather conditions contribute to elevated pathogen load to the CAWS; therefore this study determined that disinfecting the effluents of three major WRPs that discharge to the CAWS would result in an extremely small reduction in the aggregate recreation season risk to incidental contact recreators.

Dry and wet weather microbial characterization of the Chicago area waterway system.

The Chicago Area Waterway System (CAWS) is a man-made channel, which serves the Chicago area for the drainage of urban storm water and the conveyance of secondary treated effluent from the Metropolitan Water Reclamation District of Greater Chicago's (District) North Side, Stickney and Calumet water reclamation plants (WRPs). A microbial characterization of the CAWS upstream and downstream of the WRPs and from the WRP outfall was initiated by collecting dry and wet weather samples and analyzing for indicators and pathogens. During dry weather, indicator bacteria (fecal coliform [FC], E. coli [EC], enterococci [EN]) were the most abundant microbial species detected in the CAWS compared to pathogens (Salmonella spp [SA], enteric viruses [EV], adenovirus [AV], norovirus [NV] and Giardia and Cryptosporidium). Pseudomonas aeruginosa [PA] levels in the outfall samples were either lower or equivalent to the CAWS. The wet weather samples had a higher frequency of detection of indicator bacteria and pathogens compared to dry weather samples. Overall, the concentrations of pathogens in the CAWS, representing the weather conditions experienced in a recreational year, were relatively low. The study concluded that the presence of pathogens in the CAWS downstream of the WRPs were due to secondary loading of the waterway under wet weather conditions from combined sewer overflows (CSOs) and other discharges.

Antibiotic resistant bacteria in wastewater processed by the Metropolitan Water Reclamation District of Greater Chicago system.

The Metropolitan Water Reclamation District of Greater Chicago (District) initiated a research study to determine the total numbers and percentages of antibiotic resistant fecal coliform (FC) bacteria in raw sewage (RS) entering and final effluents (FE) discharged from its seven Water Reclamation Plants (WRPs). The density of FC was determined on m-FC agar containing ampicillin (ampR-16 microg/ml), gentamycin (genR-8 microg/ml), tetracycline (tetR-8 microg/ml), or all three antibiotics. The study was primarily undertaken to determine whether secondary sewage treatment at the District WRPs adequately reduces the numbers and percentages of FC(ampR), FC(tetR), FC(genR), FC(amp/tet/genR) in the FE. The numbers of ampR, tetR, genR, and amp/tet/genR FC observed in RS ranged from 2.0 x 10(5) to 1.1 x 10(7), 9.5 x 10(4) to 2.2 x 10(6), 95 to 1.5 x 10(4) and 90 to 9.5 x 10(3) per 100 mL, respectively. Secondary sewage treatment without disinfection was shown to reduce the number of antibiotic resistant FC by two-three orders of magnitude. The numbers of FC(ampR), FC(tetR), FC(genR), and FC(amp/tet/genR) observed in non-disinfected FE ranged from 2.0 x 10(2) to 6.4 x 10(3), 2.2 x 10(2) to 4.1 x 10(3), 9 to <20 and 9 to <20 per 100 mL, respectively. The relative percentages of antibiotic resistant FC observed in FE followed the same trend observed in RS: FC(ampR) > FC(tetR) > FC(genR) > FC(amp/tet/genR). Only one FC(amp/tet/genR) bacteria was found in this study indicating that multiple-antibiotic resistant FC was virtually eliminated by secondary sewage treatment. The results of multivariate regression analysis showed that the percentages of antibiotic resistant FC in the FE from all seven District WRPs were lower than the percentages of these organisms in RS (p<0.01). These results support the conclusion that secondary sewage treatment in the District effectively reduces the number of antibiotic resistant FC and that the environments of the District's seven WRPs are not conducive to the propagation or survival of antibiotic resistant fecal coliform bacteria.