Evaluation of a combined portable reverse osmosis and iodine resin drinking water treatment system for control of enteric waterborne pathogens

Three identical portable reverse osmosis-iodine resin drinking water treatment systems were evaluated for their ability to inactivate/remove Klebsiella terrigena, poliovirus type 1, rotavirus SA-11, and Cryptosporidium oocysts. The units were operated according to the manufacture's instructions for 500 hours of operation. The units were challenged with the test microorganisms after 0, 125, 250, 300, 375, 450, and 500 hours of operation. Worst case water quality challenges were done at the 60% (300 hours) and 75% (375 hours), lifetime challenge. This "worst case" consisted of 1500 mg/1 dissolved solids, 10 mg/1 organic matter, a turbidity of 30 NTU, and a pH of 9.0 at 4°C. At the 90% (450 hours) and 100% (500 hours) lifetime test the "worst case" water quality adjusted to pH 5.0 was used. The units were also tested after stagnation for 48 hours at 50%, 75%, and 100% lifetime challenges. The geometric average removals exceeded 99.9999% for the bacteria. 99.99% for the viruses, and 99.9% for the Cryptosporidium oocysts. However, on occasion, all test organisms were observed in the reverse osmosis (RO) permeate, especially when low turbidity water was processed. This demonstrated that the small rated pore size of RO membrane cannot be relied upon as an absolute guarantee of complete microorganism removal. The iodine provided additional assurance of microbial inactivation and prevention of colonization by pathogenic bacteria. The results indicate that these portable units would comply with the criteria guidelines for microbial removals under the U.S. Environmental Protection Agency's Guide Standard and Protocol for Testing Microbiological Water Purifiers.