A case study on the wastewater reclamation and reuse in the semiconductor industry

The semiconductor factory generally requires ultra pure deionized water to rinse their integrated circuit (IC) crystal chips in Taiwan. When tap water is used as the source of deionized water supply system, the reject from the devices of producing pure water (e.g. reverse osmosis, RO) usually contains less inorganic and allowed to be reused as make-up in cooling water system. The aim of this study is to evaluate the appropriateness and effectiveness of reusing the reject as cooling water for semiconductor plant. A representative semiconductor plant was selected as a case study in this paper. Calculating the typical results of water samples analysis, it was found that the cycles of concentration of this cooling water system was only 1.5, and the water stabilization index were −0.11, 8.32 and 8.86 for Langelier Saturation Index (LSI), the Ryznar Stability Index (RSI) and the Practical Scale Index (PSI), respectively. This means that the current operational condition of the cooling water system had less tendency to scale formation. Consequently, further increasing the cycles of concentration (CC) and reducing the quantity of make-up in the cooling water system would be preferable. Furthermore, the related mass balance data of used water quantities in the whole plant indicated the reuse and recovery of used water could be appropriately carried out in the plant.