This educational module is intended for state and federal regulators and practicing engineers in order to provide them a comprehensive understanding of microfiltration (MF)Microfiltration (MF) membranes: Microfiltration membranes are typically hollow-fibers with a pore size range of approximately 0.1 – 0.2 μm (nominally 0.1 μm). membranes and ultrafiltration (UF) membraneUltrafiltration (UF) membranes: Ultrafiltration membranes are typically hollow-fibers with a pore size range of approximately 0.01 – 0.05 μm (nominally 0.01 μm). applied to potable water treatment. Desirably an understanding will facilitate the use and approval of this technology. Although the examples used in the module are for new facilities, the principles are applicable to both new and retrofitted facilities. This module relies on many different information sources but the primary source is the EPA Membrane Filtration Guidance Manual (2005). Besides this reference, a valuable resource for the design, procurement, installation and commissioning of membrane systems is the ANSI/AWWA standard B110-09 (AWWA 2010).
The construction of MF and UF drinking water facilities has seen rapid growth in the last decade and has been driven by concerns for pathogensPathogens: Pathogens are disease causing microorganisms. Two of the most important pathogens driving interest in membrane systems are Giardia and Cryptosporidium. and disinfection-by-productsDisinfection-by-products (DBP’s): Disinfection-by-products are typically organic molecules such as trihalomethanes or haloacetic acids that are formed from the reaction of the disinfectant with organic materials in the water. Several such DBP’s are regulated and have maximum contaminant levels. A major consideration in selecting treatment processes and operation for many utilities is to minimize the formation of DBP’s. (DBP's). Microbes such as CryptosporidiumCryptosporidium: According to the U.S. Center for Disease Control, Cryptosporidium is a microscopic parasite that causes the diarrheal disease cryptosporidiosis. Both the parasite and the disease are commonly known as "Crypto." There are many species of Cryptosporidium that infect humans and animals. The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very tolerant to chlorine disinfection. While this parasite can be spread in several different ways, water (drinking water and recreational water) is the most common method of transmission. Cryptosporidium is one of the most frequent causes of waterborne disease among humans in the United States. are resistant to chlorine and chloramines, but membrane systems can effectively remove them by serving as an absolute barrier. This in turn reduces disinfectant use and consequent DBP formation. Indeed MF and UF membranes may potentially avoid the need to monitor for Cryptosporidium if the membrane is shown to be adequate for its removal under the Long Term 2 Enhanced Surface WaterLT2ESWTR: The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) is an EPA regulation targeting control of Cryptosporidium and other microbial contaminants. It mandates treatment efficiency, i.e., log removal values, and gives credit to various treatment technologies to achieve the needed treatment efficiency. Treatment Rule (LT2ESWTR)LT2ESWTR: The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) is an EPA regulation targeting control of Cryptosporidium and other microbial contaminants. It mandates treatment efficiency, i.e., log removal values, and gives credit to various treatment technologies to achieve the needed treatment efficiency.. Membranes are included in the toolbox which assigns credit for complying with the LT2ESWTR to achieve Cryptosporidium and GiardiaGiardia: According to the U.S. Center for Disease Control, Giardia is a microscopic parasite that causes the diarrheal illness known as giardiasis. Giardia (also known as Giardia intestinalis, Giardia lamblia, or Giardia duodenalis) is found on surfaces or in soil, food, or water that has been contaminated with feces from infected humans or animals. Giardia is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it tolerant to chlorine disinfection. While the parasite can be spread in different ways, water (drinking water and recreational water) is the most common method of transmission. treatment. Under this rule, membranes can receive a 2.5 log reduction creditLog removal value (LRV) or log reduction credit: The log removal value or log removal credit is the filtration removal efficiency for a target organism, particulate, or surrogate expressed as log10(feed concentration) – log10(filtrate concentration). for Giardia and 2 log virus reduction credit. Depending on the Cryptosporidium concentration and type of treatment, a membrane system may need no additional treatment or can receive credit up to a 5.5 log reduction for its removal/inactivation. (States may also set further regulations for using membranes to achieve Giardia and virus reduction.)
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