Fundamentals of Membranes for Water Treatment（膜对水处理的基础）.pdf

Fundamentals of Membranes for Water Treatment Alyson Sagle and Benny Freeman1 Introduction Membranes emerged as a viable means of water purification in the 1960s with the development of high performance synthetic membranes. Implementation of membranes for water treatment has progressed using more advanced membranes made from new materials and employed in various configurations. An increasing scarcity in fresh water sources fueled a push towards alternative resources such as ocean water. In the 1970s, exploration began into using membranes for water desalination. Proving successful at producing purified water from salt water, membranes became a viable alternative to evaporation-based technologies in the water treatment market. Over the years, purified water standards have become more stringent, and a plethora of new applications have appeared. However, membranes have risen to the challenge and continue to perform efficiently and effectively1. Background 1 Types of membranes. Water treatment processes employ several types of membranes . They include microfiltration (MF), ultrafiltration (UF), reverse osmosis (RO), and nanofiltration (NF) membranes (Figure 1)2 . MF membranes have the largest pore size and typically reject large particles and various microorganisms. UF membranes have smaller pores than MF membranes and, therefore, in addition to large particles and microorganisms, they can reject bacteria and soluble macromolecules such as proteins. RO membranes are effectively non-porous and, therefore, exclude particles and even many low molar mass species such as salt ions, organics, 2 etc. NF membranes are relatively new and are sometimes called “loose” RO membranes. They are porous m