AWWA WQTC58925

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 toachieve any Cryptosporidium reduction required by the rule. As a result, the MembraneFiltration Guidance Manual is being developed to assist the water treatment community with theimplementation of membrane filtration for rule compliance (USEPA 2003). Although theLT2ESWTR is only specifically applicable to the reduction of Cryptosporidium, the rule andassociated guidance nevertheless represents the first nationally standardized regulatoryframework for membrane filtration. Consequently, it is anticipated that primacy agencies mayvoluntarily adopt the LT2ESWTR regulatory framework on a broader basis for the regulation ofother pathogens, as well, including viruses.It has been firmly established that integral ultrafiltration (UF) membranes represent anabsolute barrier for the removal of viruses. Challenge studies have commonly demonstratedcomplete removal of viruses by UF membranes, ranging from 5 to 7 log reductions, dependingon the seeded concentration of the feed. However, most primacy agencies have been reluctant toaward UF even minimal virus removal credit, in large part because it is difficult to demonstratemembrane integrity on the scale that is necessary to verify that no virus-sized breaches arepresent. The LT2ESWTR regulatory framework quantifies this difficulty in terms of a resolutionrequirement for a direct integrity test that varies based on the size of the target pathogen. Underthe rule, resolution is defined as the smallest integrity breach (i.e., hole or defect) that contributesto a response from an integrity test. Consequently, by better defining the test parametersrequired to demonstrate virus-scale integrity, the LT2ESWTR regulatory framework facilitatesthe selection of an appropriate test that may enable primacy agencies to grant virus removalcredit for UF on a sound scientific basis and at their discretion. In addition, the LT2ESWTRframework also provides guidance for conducting challenge testing that can be readily translatedfrom 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 causedisease in consumers and thus are specifically regulated under the various surface watertreatment rules, the LT2ESWTR regulatory framework could also be applicable to any targetpathogen. Moreover, the same issues associated with virus removal are relevant to any relativelysmall pathogen, such as bacteria ranging in size from 0.1 to 1.0 um. Concern over pathogensspanning a wide range of sizes may be progressively more important in the future with watersecurity issues commanding increased attention across the country, and the LT2ESWTRframework can provide a standardized platform for the implementation and regulation ofmembrane filtration for removal of pathogens of all sizes.Although application of the LT2ESWTR membrane filtration regulatory framework tovirus (and other small pathogen) removal does not resolve all of the potential concerns associatedwith awarding virus removal credit to UF, it does clarify the most important issues and provideguidance for addressing these issues in a feasible manner. As a result, the LT2ESWTR frameworkrepresents a valuable tool that may help standardize and facilitate the awarding of virus removalcredit. Includes 2 references, tables.

Product Details

Edition:

Vol. - No.

Published:

11/02/2003

Number of Pages:

100

File Size:

1 file , 320 KB