Influence of pollutants on desalination effect
The pollutants that have great influence on EDI are hardness (calcium and magnesium), organic matter, solid suspended matter, valence-changing metal ions (iron and manganese), oxidants (chlorine and ozone), carbon dioxide (CO2) and bacteria.
When designing RO/EDI system, these pollutants should be removed in the pretreatment process of EDI. See section 3.2 for the concentration limits of these pollutants in the feed water. Reducing the concentration of these pollutants in pretreatment can improve EDI performance. Other EDI design strategies will be detailed in other parts of this manual.
Chlorine and ozone will oxidize ion exchange resin and ion exchange membrane, resulting in the decline of EDI module function. Oxidation will obviously increase TOC content, pollute ion exchange resin and membrane, and slow down ion migration speed. In addition, oxidation will lead to resin cracking, and the pressure loss through the module will increase. Iron and other valence-changing metal ions can catalyze the oxidation of resins and permanently reduce resins and membranes.
The performance of.
Hardness will lead to scaling in reverse osmosis and EDI devices. Scaling generally occurs on the membrane surface of concentrated water chamber, where the pH value is high. At this time, the pressure difference between the inlet and outlet of concentrated water increases and the current decreases. Campbell? Measures to avoid scaling are taken in the design of components. However, reducing the hardness of inlet water as much as possible will prolong the cleaning cycle and improve the water utilization rate of EDI system. Suspended matter and colloid
It will cause the pollution and blockage of membrane and resin, and the blockage of resin gap will lead to the increase of pressure loss of EDI components.
Organic matter is adsorbed on the surface of resin and membrane, which leads to its pollution, reduces the ion migration efficiency of polluted membrane and resin, and increases the membrane stack resistance.
Carbon dioxide has two effects. Firstly, CO32- forms carbonate scale with Ca2+ and Mg2+, and the formation of this scale is related to the ion concentration and pH value of the influent. Secondly, because the charge of CO2 is related to pH value, and the removal of CO2 by RO and EDI depends on its charge, its removal efficiency changes. Even low CO2 will significantly reduce the resistivity of product water.
The above information comes from Shenzhen Ke Rui Environmental Protection Equipment Co., Ltd. for reference only!