Shelby, Mississippi (3 cells, 72 d) Summer Winter Spring
El Paso, Texas (3 cells, 35 d) Summer Winter Spring
Beresford, South Dakota (2 cells, 62 d) Summer Winter Spring a PFU/L, plaque-forming units per liter.
Enteric Virus (PFU/L)a Influent Effluent
348 87 74
94 44 50
Source: Bausum, H.T., Enteric Virus Removal in Wastewater Treatment Lagoon Systems, PB83-234914, National Technical Information Service, Springfield, VA, 1983.
optimum number of cells needed for a particular level of pathogen removal. In general, a three- or four-cell (in series) system with an actual detention time of about 20 days will remove fecal coliforms to desired levels. Model studies with polio and coxsackie viruses indicated that the removal of viruses proceeds similarly to the first-order reaction described by Equation 3.26. Hyacinth ponds and similar aquatic units should also perform in accordance with Equation 3.26.
Pathogen removal in many wetland systems is due to essentially the same factors described above for pond systems. Equation 3.26 can also be used to estimate the removal of bacteria or virus in wetland systems where the water flow path is above the surface. The detention time will be less in most constructed wetlands as compared to ponds, but the opportunities for adsorption and filtration will be greater. The subsurface-flow wetland systems described in Chapter 7 remove pathogens in essentially the same ways as land treatment systems. Table 3.9 summarizes pathogen removal information for selected wetlands. A study of over
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