Applying the LT2ESWTR Microbial Toolbox at a Surface Water Treatment Plant

Abstract

The proposed and final versions of the Long‐Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) have not been published, but water suppliers are already gearing up for the challenges of compliance with the rule. This article discusses LT2ESWTR regulations in terms of their effect and implication for a surface water treatment plant. A case study applied the expected requirements of the LT2ESWTR to the Richmond, Virginia Water Treatment Plant (RWTP). The components of the microbial toolbox were analyzed in terms of cost, feasibility, and applicability to the Richmond facility. For RWPP, the most feasible and cost‐effective toolbox alternatives available were: a 0.5‐log credit for a watershed control program; a 0.5‐log combined filter effluent turbidity credit; a 1.0‐log demonstration of performance credit using full‐scale aerobic spore monitoring or pilot‐scale microbial challenge studies; and, inactivation with ultraviolet light. Although this study is specific to Richmond, the findings can be used by other utilities facing similar situations with similar alternatives available to them resulting from application of the microbial toolbox. This article is not available in its entirety in the printed issue of the Journal; only the expanded summary is available in print. The PDF of the entire article can be found on‐line at http://www.awwa.org.

Using spore removal to monitor plant performance for Cryptosporidium removal

“…These data indicate that the finished water concentrations were not dependent on raw water concentrations, and therefore removal was not actually described by a log‐removal function. Log removal is reported in this research in order to allow comparison with literature data and to correspond with analogous LT2ESWTR log credit concepts (Cornwell et al, 2003a).…”

“…This facility will not be able to use microbial challenge studies but can measure removal of ambient Cryptosporidium indicators, such as aerobic spores. DOP studies for RBF are unique in that these are the only opportunities to use DOP to establish upper‐bin technology credits needed for bins 3 and 4 (Cornwell et al, 2003a).…”

“…It can include monitoring of ambient aerobic spores in full‐scale treatment processes or pilot‐scale spiking studies using Cryptosporidium , aerobic spores, or some other suitable micro‐bial surrogate. Cornwell and co‐workers (2003a) described a case study illustrating that the DOP credit would likely be the most cost‐effective solution if a facility were assigned to bin 2.…”

“…One application that was specifically addressed during this project was the use of spore monitoring for the DOP credit allowed in the LT2ESWTR. DOP using aerobic spore monitoring is a potentially valuable and cost‐effective tool (Cornwell et al, 2003a) for regulatory compliance in the upcoming LT2ESWTR, particularly for facilities that need credits and do not have the resources for extensive monitoring and capital improvement requirements. The DOP credit can establish a Cryptosporidium removal credit of 4 logs or higher at existing facilities.…”

“…Details of the final rule can be reviewed in the Federal Register (USEPA, 2006a) and at the US Environmental Protection Agency (USEPA) website (USEPA, 2006b). Cornwell and colleagues (2003a) provide a brief overview of the rule as well as illustrative examples from a case study.…”