Seasonal UV disinfection of treated urban effluent. 1. Bacteriological findings

Abstract

Wastewater treated to the secondary level may not be disinfected before discharge—if the receiving waterway is not a source of drinking water‐during periods cold enough to limit recreational use. Samples were collected from a wastewater treatment plant and its receiving waterway during periods when ultraviolet disinfection of the effluent was and was not being done. Levels of Escherichia coli, fecal coliforms, and enterococci were reduced by 2 to 3 log units (99 to 99.9%) in treatment, and by more than another log unit (total 99.99% or more) with disinfection. At a sampling site ca. 30 km downstream from the outfall, levels of E. coli and fecal coliforms, but not of enterococci, were significantly higher when the ultraviolet was off. Incidence of Salmonella spp. along the waterway was not firmly related to disinfection. Probable public health effects of not disinfecting during the cold months were not clearly predictable.

Key words:

• Bacterial indicators
• Escherichia coli; Enterococci
• Fecal coliforms
• Salmonella; Receiving waterway
• Seasonal disinfection
• Ultraviolet disinfection
• Wastewater discharge

Notes

corresponding author