Membranes in Water and Wastewater Treatment

Membranes are becoming an important commodity in water and wastewater treatment. There are four major membrane categories, classified by membrane pore size, that are commercially used at the present time: Microfiltration (MF), Ultrafiltration (UF), Nanofiltration (NF) and Reverse Osmosis (RO). All four membrane categories are commonly used in water and wastewater treatment to achieve the goals of Drinking Water Guidelines and Standards. They are also used to produce desalted and/or Ultra Pure Water (UPW) for different industrial and other needs, such as power plant make up water, electronic chips manufacturing, food industry, pharmaceutical, medical and others. Membranes in wastewater treatment have lagged behind membranes used in treating water. However, the wastewater market area is growing fast, benefiting from the experience and technology issues that water applications have overcome. Nearly every known conventional water treatment technology and process has a membrane equivalent. For example, clarifiers and media filters can be successfully replaced by MF or UF membranes, softening with Cold Lime or Softeners can be achieved by substituting NF membranes, and ion exchange units can be replaced by RO membranes. Even mixed beds ion exchangers have a replacement membrane equivalent: Electro-Deionization (EDI) technology can achieve the strict standards required to produce ultra pure water (UPW) for the needs of the power and semiconductor industry. The proper and most efficient water treatment process for a particular facility has to be selected based on the specific project conditions, technical requirements, and economical parameters (capital and O&M cost). That is why the majority of membrane applications presently on the market are combinations of conventional and membrane technologies. However, a growing number of water treatment systems contain membrane processes only (membrane and/or integrated membrane system). One efficient application of membrane technology is the upgrade of existing operational plants. By implementing membrane technologies, the plant's system size (water flow), and effluent quality can be upgraded significantly at a lower relative cost than achieved by applying conventional treatment only. Most conventional processes require more chemicals to operate the system, while membrane technologies are "cleaner" processes. This presentation provides a brief history of membranes, presents the characteristics of the different types of membranes, and discusses the exponential growth in the number of installations. It will also cover applications for water recycling, water reuse and desalination, and the challenges that membrane treatment processes face. This presentation will conclude with a discussion of recent membrane developments and how these developments may impact the future of membrane applications Information provided in this presentation may help Engineers, Utilities, and Government and Private Sector representatives better understand the features and applications of membrane technologies, membrane selection and differences, evaluation and design concepts, procurement of membrane equipment, and balance of the treatment plants.