Reduction of Enteric Microorganisms at the Upper Occoquan Sewage Authority Water Reclamation Plant

Abstract

The Upper Occoquan Sewage Authority (UOSA) Water Reclamation Plant, Centreville, Virginia, is a state-of-the-art wastewater treatment plant that was created to treat area wastewater and provide protection for the Occoquan Reservoir. This study investigated UOSA's unit processes as barriers to pathogenic as well as alternative and traditional indicator microorganisms. Samples were collected once a month for 1 year from eight sites within UOSA's advanced wastewater reclamation plant. The eight sites were monitored for indicator bacteria total and fecal coliforms, enterococci, Clostridium, coliphage (the virus that infects Escherichia coli), human enteroviruses, and enteric protozoa.Overall, the plant was able to achieve a 5-to 7-log 10 reduction of bacteria, 5-log 10 reduction of enteroviruses, 4-log 10 reduction for Clostridium, and 4.6-log 10 reduction of protozoa. Total coliforms, enterococci, Clostridium, coliphage, Cryptosporidium, and Giardia were all detected in four or fewer samples of the fi nal effl uent. No enteroviruses or fecal coliforms were detected in the fi nal effl uent. The microbiological quality of reclaimed water and the reservoir water were compared. In every case, the treated wastewater was of a better quality than the ambient water in the reservoir, thus indicating that the reclaimed water will not adversely affect the water quality for downstream users. Water Environ. Res., 73, 711 (2001).

Prevalence and Persistence of Escherichia coli Strains with Uropathogenic Virulence Characteristics in Sewage Treatment Plants

“…The net outcome of the STP treatment process is recycled water with a reduced number of bacteria and, ideally, no pathogens (15). In a typical STP, the bacterial count is normally reduced by 90% (27,35); however, studies by Harwood et al (15) and Kay et al (18) have shown that approximately 67% of the initial number of total coliforms present in the primary and/or secondary sedimentation effluent can still be detected in disinfected tertiaryeffluent samples (15,18). Moreover, organisms with high initial concentrations (in influent) can still be retained at detectable levels in disinfected effluents.…”

Enterococci in the Environment

“…Comparisons of UV disinfection efficacies on a seeded laboratory strain of E. faecalis versus environmental isolates indicated that the former is more resistant (57,156,222). Meta-analyses of the existing literature indicated that chlorine disinfection considerably outperforms UV radiation in reducing concentrations of enterococci by as much as 2 orders of magnitude (58,152,182,272,273) (Table 2).…”

Mystery of Seasonality: Getting the Rhythm of Nature

“…In tropical regions, contamination of surface water increases during wet seasons. Although spread of pathogens via food is certainly possible, contaminated water is the dominant source of exposure for enteric infections caused by protozoa Cryptosporidium and Giardia (10)(11)(12). Depending on locality, outbreaks of cryptosporidiosis and giardiasis associated with drinking or recreational water frequently occur during warm or wet seasons (13,14).…”