Facility (barriers to pathogens)a

Testing Performed

Cultivable Enteric Viruses

San Diego (Aqua III, water hyacinth, ponds, dual-media filtration, UV, RO, carbon)

Concentration

Positive samples

Percent reduction

<1/1000 liters

0/32

>99.995%

Windhoek, South Africa (ponding, lime, sand filtration, chlorination, carbon)

Concentration

Positive samples

Percent reduction

1/10 liters

0/31

n.a.

Upper Occoquan Sewage Authority (lime, filtration, carbon, chlorination)

Concentration

Positive samples

Percent reduction

<1/500 liters

0/11

>99.995%c

a All testing is on final effluent unless otherwise noted. Carbon = carbon adsorption; lime = chemical lime treatment, pH 11.2, recarbonation; RO = reverse osmosis; UF = ultrafiltration; UV= ultraviolet disinfection.

b After filtration.

c Based on raw sewage counts; all other removals based on counts entering reclamation facility.

Factory 21 reclamation plant, in 1979 and 1981. In the 1979 study(James M. Montgomery, Inc., 1979), one of the 142 final, disinfected effluent samples was positive for viruses, and the study recommended that the disinfection procedure be optimized to increase the contact time and to increase chlorine residual to 5 mg/liter. In the second study (James M. Montgomery, Inc., 1981), no samples were positive for viruses in the final effluent, an improvement due to improved disinfection and the reduction of influent virus levels by upgrading the secondary treatment from a trickling filter effluent to an activated sludge system. This study also demonstrated that reverse osmosis was not a good substitute for disinfection. Without disinfection, 5.3 percent of the samples from reverse osmosis effluent still contained viruses. Studies conducted by San Diego during the Aqua II project also noted relatively high virus breakthrough in reverse osmosis systems (Western Consortium for Public Health, 1992). During the Tampa project, viruses were detected in 6.7 percent of the samples after chlorination, but this occurred during an operational period when pH levels were suboptimal during lime treatment and there was a loss in normal chlorine residuals (Western Consortium for Public Health, 1992).



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