Enterococci

Coliphage

Enterovirus

Cryptosporidium Oocysts

Giardia Cysts

5 x 105

3.8 x 105

1,085

1,484

4.9 x 104

NT

2.8 x 106

1,000

1,500

6.9 x 103

6,400

3.8 x 104

71,000

NT

NT

NT

NT

7,000

30

3,900

NT

NT

5 x 103 4 x 104

NT

NT

NT

NT

2 x 103

2 x 102

3.25 x 104

Fecal streptococcib 7,000

5 x 104

NT

100

200

a Data reported from three reclamation plants.

b All fecal streptococci measured.

wastewater. However, some protozoa and parasite ova and cysts will settle out during primary treatment, and some particulate-associated microorganisms may be removed with settleable matter.

Secondary treatment, however, is designed to remove soluble and colloidal biodegradable organic matter and suspended solids. In some cases it also removes nitrogen and phosphorus. Secondary treatment consists of an aerobic biological process whereby microorganisms oxidize organic matter in the wastewater. The aerobic biological processes include activated sludge, trickling filters, rotating biological contactors, and stabilization ponds. Generally, primary treatment precedes these biological processes; however, some secondary processes, such as stabilization ponds and aerated lagoons, are designed to operate without sedimentation. Table 3-7 lists typical microorganism removal efficiencies for activated sludge and trickling-filter secondary treatment processes.

Conventional secondary treatment reduces pathogens but does not eliminate them from the effluent, even with disinfection. A Florida sur-



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