ELECTRODEIONIZATION (EDI) FOR PURIFICATION OF HIGH SALINITY WATER

• Main Author: Nurul Hakim, Ahmad
• Format: Dissertations
• Language: Indonesia
• Subjects: Teknik kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/32604
• Institution: Institut Teknologi Bandung

Seawater desalination has become a choice of supplying water demand for domestics and industrial. Nowadays, seawater desalination process is still dominated by reverse osmosis technology. However, reverse osmosis suffers a higher degree of complexity related to the high-pressure operation. Electrodeionization (EDI) is a potential alternative for reverse osmosis since it can be operated in a low-pressure operation. EDI utilizes electrical potential difference as the driving force for ion transport and ion exchange membrane as an ion-selective barrier. Generally, EDI is used for low salinity water purification producing ultrapure water. Yet, application of EDI in seawater desalination is still not found. EDI has some principle drawbacks, such as high module resistance, back diffusion, and resin re-orientation which hinder its application. This research is focused on solving these problems. Module resistance will be lowered by optimizing spacer thickness, back diffusion flux will be minimized by the two-stage desalination, and re-oriented resin will be dispersed by flow reversal configuration. The result confirmed the capability of EDI process in high salinity water desalination with the highest removal of 94.46% and the lowest specific energy consumption of 11.67 kWh/m3. The highest removal is achieved by using EDI module with spacer thickness of 4 mm which is operated at applied voltage of 20 volt, flow rate of 2 ml/s, and recovery of 75%. ANOVA test indicated that the effect of circulation laju alir is insignificant. Long-term performance test confirms performance stability of EDI in seawater desalination with maximum performance drop less than 1.5%. Scaling test shows that EDI module with spacer thickness of 12 mm is more susceptible to scaling. It is observed that scaling is more concentrated in anion-exchange membrane rather than cation-exchange membrane. Recirculation cleaning can recover EDI performance up to 94.66% while combination of cleaning followed by module disassembly can recover its performance up to 99.00%. Accelerated scaling test shows that precipitation of solid in membrane and ion-exchange surface lead to resin re-orientation and pressure increase at concentrate compartment. Reverse flow procedure conducted when concentrate pressure reach 1.5 bar is able to maintain performance stability of EDI. The result also indicated that diluate filled EDI configuration shows better performance than all filled EDI configuration. Development of the mathematical model for EDI process was conducted in stage 3 of the research based on porous plug model and simple mass balance equation to describe ion transport ion EDI. v The calculated result showed a good agreement with experimental data with the mean error of less than 10%. Combined chemical precipitation-ultrafiltration (UF) process is able to achieve Ca2+ removal up to 93.36% and Mg2+ removal up to 87.60%. Polysulfone UF membrane with cross flow configuration exhibits the most stable configuration with performance decline less than 20% during 250 minutes of filtration. Periodic backwash is recommended to maintain performance stability of UF. Accelerated scaling test of EDI for pretreated feed water shows that combined chemical precipitation-UF process is able to maintain performance stability of EDI with less than 5% removal drop at the end of 10th batch.