TABLE 3-10 Concentrations of Parasites and Viruses in Disinfected Secondary Effluents Used for Crop Irrigation in Arizona

Microbial Agent

Plant 1 Activated Sludge (aeration, chlorination)

Plant 2: Activated Sludge (aeration, denitrification, chlorination)

Giardia cysts/100 liters (positive samples)

66.8 (5/5)

1.57 (2/4)

Cryptosporidium oocysts/100 liters (positive samples)


No data

Enteroviruses PFU/100 liters (positive samples)

0.125 (3/52)


NOTES: Numbers in parentheses are number of positive samples per total samples taken. Treated wastewater is being used for cotton crop irrigation. The Arizona standard for public access irrigation was less than 2.5 PFU or cysts per 100 liters.

states that greater reductions may be required if a source water is of poor quality. Due to the lack of monitoring information, EPA has recently promulgated the Information Collection Rule, or ICR, to develop an occurrence database for Cryptosporidium, Giardia, and viruses in source waters, in some treated waters, and in various treatment processes. In light of a national move toward watershed-based requirements, the ICR will likely influence future microbial standards and monitoring requirements pertaining to both planned potable reuse projects and potable water supplies influenced by upstream wastewater discharges.

Microbial Data From Nonpotable Reuse Applications

Arizona is currently the only state with standards and required monitoring for concentrations of viruses and Giardia in reclaimed water. Arizona's current standard is less than or equal to 1 cyst or viral PFU per 40 liters (2.5 cysts or PFU/100 liters). The following sections summarize the monitoring data available from Arizona, as well as the results of specific microbial studies from California and Florida based largely on tertiary-treated wastewater (secondary treatment, filtration, and chlorination) used for nonpotable reuse applications.

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