Plant 3: Lagoon (5 days retention time, mechanical aeration, UV light disinfection)

Plant 4: Biotowers (compressed air, chlorination)

Plant 5: Activated Sludge (oxygen, chlorination)

Plant 6: Lagoon (mechanical aeration, chlorination)

18.3 (6/11)

26 (35/38)

43.5 (36/42)


11.4 (2/2)

3.4 (16/30)

3.7 (15/34)

1.5 (2/5)

7.75 (11/45)

0.725 (6/16)

0.75 (3/47)

No data

SOURCE: C. P. Gerba, personal communication, 1996.

Microbial Monitoring in Arizona

Data on concentrations of Giardia, Cryptosporidium, and enteroviruses are available from wastewater and reclamation facilities in Arizona where the effluent is used for irrigation. Arizona currently has no requirements for monitoring of Cryptosporidium in reclaimed waters; however, this protozoan was included in most monitoring programs. Monitoring frequency is established on a case-by-case basis and is determined partly by the flow, treatment design, and designated reuse application. Frequency ranges from once per month to twice per year. Table 3-10 summarizes the monitoring results for six reclamation facilities that use a variety of secondary treatment options followed by disinfection with chlorination or ultraviolet light. The effluents were used primarily for irrigating cotton crops.

Collectively, Giardia was found in 78.5 percent of the effluent samples from all plants at an average concentration of 31.3 cysts/100 liters. Cryptosporidium was found in 59 percent of the samples from all plants at an average concentration of 5 oocysts/100 liters. Viruses were found in 18 percent of the samples from all plants at an average concentration of 2.2 most probable number (MPN) PFU per 100 liters. No differences in protozoa levels were readily detected in the two plants using lagoon effluents.

Table 3-11 illustrates the efficacy of combining sand filtration and

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