The US-Environmental Protection Agency (US-EPA) in their 1992 guidelines has recommended the use of much stricter standards for wastewater use in the USA, than those recommended by the WHO. The main guideline is that fecal coliforms should not exceed 14 MPN/100 ml in any sample, which in practice means not detectable. Secondary treatment should be used followed by filtration (with prior coagulant and/or polymer addition) and disinfection. In addition, the US-EPA guidelines set standards indicating the type of treatment required, the resultant water quality specifications, and the appropriate setback distances. The elements of the guidelines applicable to reuse in agriculture are summarized in table 5.



Legend: SS= suspended solids; FC= fecal coliforms

Footnotes:

¹These guidelines are based on water reclamation and reuse practices in the U.S., and they are especially directed at states that have not developed their own regulations or guidelines. While the guidelines should be useful in many areas outside the U.S., local conditions may limit the applicability of the guidelines in some countries.
²Secondary treatment processes include activated sludge processes, trickling filters, rotating biological contractors, and many stabilization pond systems. Secondary treatment should produce effluent in which both the BOD and SS do not exceed 30 mg/l.
³The number of fecal coliform organisms should not exceed 14/100 ml in any sample.
⁴The number of fecal coliform organisms should not exceed 800/100 ml in any sample. Some stabilization pond systems may be able to meet this coliform limit without disinfection.

Table 5: US-EPA/USAID Guidelines for agricultural reuse of wastewater (adapted from suggested guidelines for water reuse (US-EPA/USAID, 1992) [Source: EPA, Process Design Manual: Guidelines for Water Reuse, Cincinnati, Ohio, 1992: Report No. EPA-625/R-92-004] ¹

For irrigation of crops likely to be eaten uncooked, no detectable fecal coliforms/100 ml are allowed (compared to ≤ 1000 FC/100 ml for WHO), and for irrigation of commercially processed crops, fodder crops, etc, the guideline sets ≤ 200 FC/100 ml (where only a nematode egg guideline is set by WHO). No nematode egg guideline is specified by US-EPA. Actual standard setting is the responsibility of individual states in the USA, and different US-States take different approaches (some specify treatment processes, others specify water quality standards) and a range of standards are in use. Standards in several countries have been influenced by American standards, especially the Californian standards.