Presentation Title

Persistence of sewage-derived bacteria and viruses in soil

Faculty Mentor

Natalie Mladenov

Start Date

23-11-2019 10:00 AM

End Date

23-11-2019 10:45 AM

Location

169

Session

poster 3

Type of Presentation

Poster

Subject Area

engineering_computer_science

Abstract

Sewage spills and leakage from sewer infrastructure can pose health and environmental risks associated with exposure to pathogenic bacteria, viruses, and other microorganisms. During storm events, sanitary sewer overflows may also occur and result in sewage contamination of soils. The main objectives of this research are to study the persistence of bacteria and viruses in soils and to understand their decay rates. Soil samples were collected from the riparian zone adjacent to Alvarado Creek, a tributary to the San Diego River. Soil samples were placed into sterilized falcon tubes that were spiked with untreated wastewater collected from a water reclamation facility. These samples were kept dry in a biosafety cabinet at ambient temperature and analyzed for dissolved organic carbon (DOC), total dissolved nitrogen (TDN), fecal indicator bacteria (FIB: total coliforms and E. coli), Pepper Mild Mottle Virus (PPMoV), and Bacteroides HF183. Two experimental treatments were applied, one in which spiked soils, left to dry overnight, were then repeatedly flushed with synthetic rainwater (flushing treatment) and one in which spiked soils, dried for different durations (1, 7, 14, 28, 60 and 121 days), were subsequently flushed once with synthetic rainwater (decay treatment). Both experimental treatments were performed in duplicate. For the flushing treatment, FIB concentrations showed a 2- to 3-log reduction and HF183 showed a > 3-log reduction. However, 104 to 106 MPN/100mL of FIB were still detected after 20 flushes. After the long-term drying of spiked soil, there was a > 5-log reduction of E. coli, > 3-log reduction of HF183, and only <1-log reduction of PMMoV. Decay rates were -0.197 to -0.219 d-1 for E. coli, -0.0813 to -0.107 d-1 for HF183, and -0.028 to -0.037 d-1 for PMMoV, reflecting the greater resistance of PMMoV to degradation. Also, after 60 days there was 100 - 1,000 MPN/100 ml of E. coli, PMMoV and HF183 still detected. These results indicate that, despite some reduction in bacterial and viral concentrations, the microbial markers evaluated in this study were still present and viable in soils after extensive flushing and long term drying.

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Nov 23rd, 10:00 AM Nov 23rd, 10:45 AM

Persistence of sewage-derived bacteria and viruses in soil

169

Sewage spills and leakage from sewer infrastructure can pose health and environmental risks associated with exposure to pathogenic bacteria, viruses, and other microorganisms. During storm events, sanitary sewer overflows may also occur and result in sewage contamination of soils. The main objectives of this research are to study the persistence of bacteria and viruses in soils and to understand their decay rates. Soil samples were collected from the riparian zone adjacent to Alvarado Creek, a tributary to the San Diego River. Soil samples were placed into sterilized falcon tubes that were spiked with untreated wastewater collected from a water reclamation facility. These samples were kept dry in a biosafety cabinet at ambient temperature and analyzed for dissolved organic carbon (DOC), total dissolved nitrogen (TDN), fecal indicator bacteria (FIB: total coliforms and E. coli), Pepper Mild Mottle Virus (PPMoV), and Bacteroides HF183. Two experimental treatments were applied, one in which spiked soils, left to dry overnight, were then repeatedly flushed with synthetic rainwater (flushing treatment) and one in which spiked soils, dried for different durations (1, 7, 14, 28, 60 and 121 days), were subsequently flushed once with synthetic rainwater (decay treatment). Both experimental treatments were performed in duplicate. For the flushing treatment, FIB concentrations showed a 2- to 3-log reduction and HF183 showed a > 3-log reduction. However, 104 to 106 MPN/100mL of FIB were still detected after 20 flushes. After the long-term drying of spiked soil, there was a > 5-log reduction of E. coli, > 3-log reduction of HF183, and only <1-log reduction of PMMoV. Decay rates were -0.197 to -0.219 d-1 for E. coli, -0.0813 to -0.107 d-1 for HF183, and -0.028 to -0.037 d-1 for PMMoV, reflecting the greater resistance of PMMoV to degradation. Also, after 60 days there was 100 - 1,000 MPN/100 ml of E. coli, PMMoV and HF183 still detected. These results indicate that, despite some reduction in bacterial and viral concentrations, the microbial markers evaluated in this study were still present and viable in soils after extensive flushing and long term drying.