There are dissolved substances such as sodium, calcium, magnesium, chloride, nitrate, bicarbonate, etc. in general urban water sources. These compounds are composed of negatively charged anions and positively charged cations. The campus direct drinking water project can remove over 99% of ions through reverse osmosis pretreatment. In addition, the raw water may also contain other trace elements, dissolved gases (such as CO2), and some weak electrolytes (such as boron and silicon dioxide), which must be removed in industrial desalinated water. However, the reverse osmosis process has poor removal efficiency for these impurities.
The working principle of ion exchange membrane and ion exchange resin in campus direct drinking water project is similar, which can facilitate the migration of specific ions. Anion exchange membranes only allow anions to pass through and do not allow cations to pass through; And cation exchange membranes are exactly the opposite. The integrated direct drinking water dispenser is filled with mixed ion exchange resin between a pair of cation exchange membranes to form an EDI unit. The space occupied by the mixed ion exchange resin between the anion and cation exchange membranes is called a freshwater chamber. Arrange a certain number of EDI units together, alternating between anion exchange membranes and cation exchange membranes, and use a mesh to separate each EDI unit to form a concentrated water chamber. Driven by a given DC voltage, in the fresh water chamber, the cations and anions in the ion exchange resin migrate towards the positive and negative electrodes under the action of an electric field, and enter the concentrated water chamber through the cation exchange resin. At the same time, the ions in the campus direct drinking water project water are adsorbed by the ion exchange resin and occupy the vacancies that flow down due to ion electromigration. In fact, the migration and adsorption of ions occur simultaneously and continuously. Through this process, ions in the feedwater pass through the ion exchange membrane and enter the concentrated water chamber for removal, becoming desalinated water.
