An analysis of organic removal and its use as an integrity monitoring method in ultrafiltration membrane systems

New regulations in the drinking water treatment industry in North America require that UF membranes be monitored for integrity at all times using indirect integrity monitoring methods such as turbidity, particle counting or particle monitoring. Current methods are not able to reliably detect tiny pinholes that may allow the passage of pathogens such as Giardia lamblia or Cryptosporidium. There is a need for novel indirect integrity monitoring methods that are sensitive enough to detect small holes but that are also simple and user-friendly enough to be widely adopted.;This project consisted of four major experiments. The first was an investigation of organic removal in pilot-scale membrane systems. The results of this study were used to develop a bench-scale testing unit that mimicked the organic removal capabilities of a larger system. The next series of experiments involved a wide-ranging survey of factors affecting organic removal in the bench-scale UF system including variations in water quality, turbidity removal, coagulation pretreatment and recycling backwash water with and without residual coagulant. A proof of concept trial was then conducted to determine the feasibility of using NOM as an integrity indicator. This experiment found that UV254 absorption measurements and specific UV absorption (SUVA) values in the UF permeate corresponded to breaches in the membrane surface. The final set of experiments was designed to compare an intact membrane and breached membranes operated in various process design configurations. This last experiment determined that small pinhole breaches can in some cases be detected by observing organic removal, as measured by TOC, UV254, SUVA and differential UV absorbance however, other factors such as coagulation pretreatment can overwhelm these effects and make the method ineffective.;Removal of natural organic matter (NOM) is already a priority for utilities because if left untreated, many of these molecules will react with chlorine during the disinfection step to form disinfectant by-products (DBPs). UF membranes are capable of removing a portion of NOM through a combination of physical sieving and electrostatic forces. However, because most NOM present in surface water is dissolved, not all of it will be removed by the UF. Many utilities employ coagulation pretreatment in order to remove more NOM and fulfill the requirements of the current guidelines.