Under the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR),
membrane filtration is designated as one of the "toolbox technologies" that may be used to
achieve any Cryptosporidium reduction required by the rule. As a result, the Membrane
Filtration Guidance Manual is being developed to assist the water treatment community with the
implementation of membrane filtration for rule compliance (USEPA 2003). Although the
LT2ESWTR is only specifically applicable to the reduction of Cryptosporidium, the rule and
associated guidance nevertheless represents the first nationally standardized regulatory
framework for membrane filtration. Consequently, it is anticipated that primacy agencies may
voluntarily adopt the LT2ESWTR regulatory framework on a broader basis for the regulation of
other pathogens, as well, including viruses.
It has been firmly established that integral ultrafiltration (UF) membranes represent an
absolute barrier for the removal of viruses. Challenge studies have commonly demonstrated
complete removal of viruses by UF membranes, ranging from 5 to 7 log reductions, depending
on the seeded concentration of the feed. However, most primacy agencies have been reluctant to
award UF even minimal virus removal credit, in large part because it is difficult to demonstrate
membrane integrity on the scale that is necessary to verify that no virus-sized breaches are
present. The LT2ESWTR regulatory framework quantifies this difficulty in terms of a resolution
requirement for a direct integrity test that varies based on the size of the target pathogen. Under
the rule, resolution is defined as the smallest integrity breach (i.e., hole or defect) that contributes
to a response from an integrity test. Consequently, by better defining the test parameters
required to demonstrate virus-scale integrity, the LT2ESWTR regulatory framework facilitates
the selection of an appropriate test that may enable primacy agencies to grant virus removal
credit for UF on a sound scientific basis and at their discretion. In addition, the LT2ESWTR
framework also provides guidance for conducting challenge testing that can be readily translated
from Cryptosporidium to viruses, thus allowing primacy agencies to establish a conservative,
product-specific virus removal efficiency for an integral membrane filtration process.
While viruses are a pathogen of significant concern because low numbers can cause
disease in consumers and thus are specifically regulated under the various surface water
treatment rules, the LT2ESWTR regulatory framework could also be applicable to any target
pathogen. Moreover, the same issues associated with virus removal are relevant to any relatively
small pathogen, such as bacteria ranging in size from 0.1 to 1.0 um. Concern over pathogens
spanning a wide range of sizes may be progressively more important in the future with water
security issues commanding increased attention across the country, and the LT2ESWTR
framework can provide a standardized platform for the implementation and regulation of
membrane filtration for removal of pathogens of all sizes.
Although application of the LT2ESWTR membrane filtration regulatory framework to
virus (and other small pathogen) removal does not resolve all of the potential concerns associated
with awarding virus removal credit to UF, it does clarify the most important issues and provide
guidance for addressing these issues in a feasible manner. As a result, the LT2ESWTR framework
represents a valuable tool that may help standardize and facilitate the awarding of virus removal
credit. Includes 2 references, tables.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 320 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 100 |
| Published : | 11/02/2003 |
