Membrane is a technology that has many advantages and is applied to water purification production in various countries including Japan, the United States, Singapore, and Australia. Twenty-seven water purification plants are operating in Korea, starting in 2004. And among these water purification plants are plants with an operating period of 15 years.
If the membrane is damaged due to mechanical impact, or if the membrane is damaged by scratching the surface of the membrane, find and repair the damaged part of the module through testing, or replace the module with a spare module. However, prolonged use of membranes can degrade the performance of the membrane due to fouling or deformation, and the original filtration performance cannot be restored even after the cleaning of the chemical. When this condition is reached, replacement is considered. And there are no guidelines regarding the performance evaluation or replacement of modules.
In the case of the G water purifier selected for research, the performance guarantee period suggested by the manufacturer is seven years, and the facility is currently in operation after nine years. It is already in use after the performance guarantee period guaranteed by the manufacturer. The purpose of the project was to analyze the operation status and conduct a performance assessment for each group to prepare for accidents caused by sudden rise in pressure or lack of flow rate.
In this study, the performance of membrane modules is analyzed by dividing items into treatment water quality assessment, production quantity evaluation, membrane durability assessment, and operation cost evaluation through analysis of operational data and testing devices of G water purification plant. Through the analysis results, it is required to check the performance change of the membrane in each group, analyze the causes, and first select the targets that need to be replaced and present the criteria.
As a result of the performance evaluation of the treated water quality, the turbidity of the treated water in the second and forth group was good. But the cumulative number of pin repairs in the second group was 1,462. The pore size in the second group had been larger than the first group.
As a result of the assessment of production quantity, recovery rate of recovery washing was the degradedest in the second group. The second group also had the highest frequency of recovery cleaning. On the other hand, the porosity of first group was lower than the second group.
Based on the results of the membrane durability evaluation, it was judged that the durability of the second group was reduced, rather than the first group, considering the elongation rate and tensile strength. Considering the link between break ratio of fiber and membrane durability, it is believed that the third and fourth groups will be similar physical strength of the first group.
According to the assessment of operating costs, it was found that the differential pressure increase rate was in the order of second > fourth > third > first group, and the power source unit and chemical cost were good.
Based on the above findings, the second group module with the lowest performance in the items of pin repair count, pore size, wash recovery rate, elongation rate, and differential pressure increase rate were selected as the targets for replacement. Performance evaluation of the remaining 1, 3 and 4 group will be conducted every year to determine the replacement target and timing.
I hope that this research result can be used as a basic data in the future in establishing the standard manual for performance evaluation and membrane module replacement guidelines.