Keynote lecture Marcin KŁOS

Lime softening as a pretreatment method before an EDR process

The technological and economic efficiency of the operation of membrane installations in desalination and demineralization systems largely depends on the quality of the raw water feeding the desalination installation. Ensuring appropriate water quality allows to reduce the fouling and scaling phenomena, which have an extremely negative effect, especially on high-pressure membrane processes. Although the fouling resistance of the membranes used in Electrodialysis Reversal (EDR) is significantly higher than that of osmotic membranes, some types of impurities can significantly degrade them. This group includes Natural Organic Matter (NOM), which the negative impact on the condition of ion exchange resins is well known.

The article presents the results of laboratory and technical scale tests conducted as part of the optimization of the operation of the preliminary water treatment system feeding the EDR unit. This system was based on the conventional treatment processes used for the preparation of industrial water, i.e. lime softening, carried out simultaneously with coagulation using iron salts, and on rapid filtration. In the course of the tests, it was found that the presence of NOM, and humic compounds in particular, has a crucial influence on the operational parameters of the EDR installation, such as: desalination efficiency, hydraulic losses of the flow through the unit and the frequency of CIP procedures. Removal of these substances in the lime softening process is not an easy task and requires a specific approach to the selection of the most advantageous process conditions. The obtained test results showed that the most effective way to control the NOM concentration in the terms of the presence of humic compounds in the adopted water pre-treatment technology is the appropriate control of the coagulant dose, allowing for effective removal of organic pollutants while maintaining the required chemical softening effects.

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