AWWA MTC57667

Surface Water Treatment Regulations (SWTR) demand that there is a method to verify that the treatment of surface water removes a certain percentage of microorganisms. In membrane filtration, which in this paper means the pressure driven processes microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO), the permeate has passed through a filter with pore size below 1 um. Thus, with membrane devices without any defects, there should not be any microorganisms of size greater than 1 um in the permeate. However, defects in the membrane or in the seals that separate the permeate side from the feed side might allow big microorganisms to pass through to the permeate side. The Vacuum Decay Test (VDT) is one method to approximately determine how high percentage of the permeate from a membrane unit has bypassed the intact membrane, and passed through defects of size about 1 um or larger. This report describes how the VDT can be applied to spiral wound RO (reverse osmosis) elements. The Vacuum Decay Rate (VDR) was measured for housings containing four 8-inch diameter elements, up to three housings together. This was done with intact elements, and after poking one or more holes in the membrane in one element, and when an O-ring had been damaged. The VDR was used to predict the bacteria passage, and these predictions were compared to the actual bacteria passages in following tests. Includes 3 references, tables, figures, appendices.