. "4 Methods for Assessing Health Risks of Reclaimed Water." Issues in Potable Reuse: The Viability of Augmenting Drinking Water Supplies with Reclaimed Water. Washington, DC: The National Academies Press, 1998.
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Arizona is the only state that has standards for the concentration of enteric viruses and Giardia in reclaimed water; it is also the only state in which water reuse is regulated by a laboratory certification program, although specialized studies have been undertaken in Florida and California for viruses and protozoa.
To address the lack of information nationwide on levels of viral and protozoan pathogens and the efficacy of water treatment, EPA promulgated the Information Collection Rule (ICR) in 1996. Detection processes for the enteroviruses by cell culture and for protozoa by microscopy have been standardized for this rule, and laboratories are undergoing an approval process. The data will be used in future risk analyses to establish the necessary drinking water treatment performance criteria for the protection of public health. The results will be applicable to potable reclamation projects as well. However, when considering wastewater as a source of drinking water, particular attention should be paid to current limitations and other issues involved with the methodology used to detect microbial pathogens.
Microbial Detection Methods
Microbial detection methods can be described and compared in terms of recovery (the efficiency of the method for collecting microorganisms from water samples), sensitivity (a measure of the minimum number of microorganisms that can be detected per unit volume), and specificity (the proper taxonomic identification of the microbial agent). No method is 100 percent efficient; estimates of recovery tend to range from 5 to 60 percent. A method's sensitivity is often expressed as a detection limit, such as 1/100 ml, meaning that it is able to detect one microorganism in a 100 ml sample. In untreated wastewater, concentrations of microorganisms can be high enough to be readily detected in small test volumes. However, such methods are not sufficiently sensitive for testing the highly treated reclaimed water typically produced by potable reuse projects. With highly treated reclaimed water, larger volumes of water are needed for analysis, and microorganisms may occur at concentrations too low to be detected.
Table 4-1 presents the major microbial detection techniques as they are applied to the detection and quantification of bacteria, viruses, and protozoa. Culture techniques have long been used for the detection and enumeration of viable bacteria and viruses, while microscopy techniques have a long history in the identification of bacteria and protozoa.
Table 4-2 summarizes the advantages and disadvantages of some methods for evaluating the microbiological quality of reclaimed water. The polymerase chain reaction (PCR) has only recently been applied to