Pilot-scale Study On Seawater Desalination Pretreatment With Hollow Fiber Ultrafiltration Membrane

As a kind of fresh water resource increment technology, seawater desalination develops rapidly in China in recent years.By June 2007, total capacity of national seawater desalination projects had exceeded 13×104 m3/d. Some ultra-large scale seawater desalination projects are under construction or planing. According to"Seawater Utilization Programme", which was issued in 2005 by National Development and Reform Commission, State Oceanic Administration and Ministry of Finance, till 2010, total capacity of national seawater desalination projects will reach 80 ~ 100×104 m3/d.Ultrafiltration (UF) is a kind of emerging pretreatment technology for reverse osmosis seawater desalination (SWRO), which uses physical method to trap solid suspended substance, colloid and microbe in seawater, to meet feedwater quality requirements of RO membrane. Comparing with conventional pretreatment process, it has its advantages, such as low in turbidity and silt density index (SDI) of product water, less footprint required and easier in oparetion besides its product water quality won't be affected by temperature. Therefore, it is being more and more adopted in SWRO projects.Though it has prominent technical advantages, some key technical problems are still not solved, which impede the application of UF in large-scale SWRO projects. These key problems are as follows: pretreatment before UF filtration, structure design of UF membrane module, design of UF system and running parameter optimization, etc.A power plant located in the North China plans to build a SWRO project with a capacity of 1×104 m3/d, UF filtration techonlgy was chosen as seawater pretreatment. In this sea area, turbidity of seawater is low without wind and wave, usually around 10 NTU, and 20~130 NTU with wind and wave, and average turbidity is below 20 NTU. In winter, temperature is lower, about 4℃.In order to choose suitable UF membrane and determining operation parameters, parallel comparing pilot-scale tests with three sorts of hollow fiber UF membrane were carried out. The pilot-scale tests were divided nito four phases, up to 1000 hrs, we focus on trans-membrane pressure (TMP), specific flux, permeate SDI, permeate turbidity and operating power consumption, etc.The pilot-scale tests come to the conclusions that chemical cleaning is the primary factor that affects horizontally installed hollow fiber UF membrane, and gas flushing is the primary factor that affects vertically installed hollow fiber UF membrane.