UV Inactivation of Indigenous Male Specific and Somatic Coliphages, and Treatment Implications
- Thomas Worley-Morse, Melanie Mann - Hazen and Sawyer
- Mike Sasges
- Raul Gonzalez - Hampton Roads Sanitation District
- Linda Gowman - Trojan Technologies Inc
The United States (US) Environmental Protection Agency (EPA) is required to review its guidelines on Recreational Water Quality Criteria (RWQC) every five years, and criteria were last released in 2012. As part of the 2017 review, the EPA is considering the use of coliphages as possible indicators of fecal contamination in ambient water. Coliphages are bacteriophages that infect E. coli, and as such are expected to correlate with coliform contamination. In addition, since they are viruses it is expected that their fate in the environment should correlate with that of pathogenic viruses. In 2015 The EPA published a review of literature on coliphages and stated that “EPA will evaluate the development of coliphage-based ambient water quality for the protection of swimmers”.
While the correlation between coliphages and pathogens, or between coliphages and illness is an active area of debate, it seems likely that a new EPA guideline will be formulated related to coliphage. The impact of a coliphage RWQC and coliphage state water quality standards on the sizing and operation of wastewater treatment plants is unknown, but could easily require millions of dollars of upgrades. In order to understand the impact of a future guideline on UV disinfection, a study was undertaken to determine the concentration of indigenous coliphages in secondary effluent, and the UV sensitivity of these indigenous organisms. This information may be used to predict the impact of future regulations on UV system performance and sizing to achieve desired coliphage discharge levels.
The present study sought to evaluate the concentration and UV sensitivity of indigenous phages from four different wastewater treatment plants located in the Mid-Atlantic Region.
Non-disinfected effluent samples were collected from the outlet of the secondary clarifiers in each plant. Samples were collected once per month from November 2016 through June 2017. Some samples were not collected, or were damaged during handling, and as a result are not included in the following analysis. The effluent as received from the treatment plants had 254nm UV transmittance of 50% to 70% per cm, with an average of 64%. The TSS ranged from 0.3 to 17, with an average of 6.1 mg/L.
Samples were shipped to GAP Enviromicrobial Services (London, ON) where phage enumerations were conducted using EPA method 1602, a Single-Layer Agar procedure that evaluates plaque formation on a host lawn of E. coli specific to the targeted type of phage (somatic or male specific). GAP conducted UV irradiations in stirred samples following the procedure of Bolton and Linden (2003).
RESULTS AND CONCLUSIONS
The somatic coliphage concentrations were generally higher than the male specific concentrations. There were no general trends with season in this data. The measured data generally falls within the range of 102 to 104 PFU/100 ml, slightly lower than the range of 102 to 106PFU/100 ml reported in the 2015 EPA review.
As may be seen from these plots, the disinfection kinetics are not always first order; many of the log-linear plots have curvature. The curvature in these inactivation plots is in contrast to the well-characterized somatic phage T1UV which is used extensively in evaluation of UV reactors. T1UV displays first-order kinetics over at least 5 log of inactivation, with a dose per log of about 5mJ/cm2/log. The tailing in the inactivation curves, likely as a result of having eliminated the weaker species with the low doses, leaves the more resistant species to be inactivated with higher doses.
Regarding UV sizing and discharge levels, a typical UV installation for secondary effluent in North America is often designed to achieve 10-20 mJ/cm2, based on current indicator organisms (e.g. fecal coliform, E. coli, and enterococci). The outcome is strongly dependent on the particular plant effluent. WWTP A would have somatic phage concentrations from 7 to 93 PFU/100 ml, while WWTP B would consistently achieve discharge levels of 1 or zero PFU/100 ml at the same UV dose. If the discharge permit were set at 10 PFU/100 ml, and the plants installed UV systems applying 16mJ/cm2, WWTPs A and D would be out of compliance about half the time, while WWTPs B and C would be in compliance most or all of the time.
These results suggest coliphage inactivation kinetics are not consistent from plant to plant. In some cases, significant tailing was observed, which suggests increased doses may be required to meet low level effluent coliphage concentrations.
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