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ISSN 1811-0231 / ISEIS Publication Series Number P002

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  Paper EIA06-020, Volume 4 (2006), Pages 233-243 = complimentary

The strategy to optimize the water recycle in LCD plants

C. W. Hsu1, C. Y. Tsai1, C. N. Chang1* and A. C. Chao2

1. Department of Environmental Science and Engineering, Tunghai University, Taichung City, Taiwan 407, ROC. *Corresponding author: cnchang@thu.edu.tw.

2. Department of Civil Construction and Environmental Engineering, North Carolina State University, Raleigh, North Carolina, USA.

 

Abstract

Some hi-tec industries, e.g. TFT-LCD manufacturing, require a larger quantity of water than traditional industries. In Taiwan, the current water price is relatively low; TFT-LCD industries enjoy the competitive edge that may be partly contributed by the availability of less-expensive water. Since the water resources are becoming scarce in Taiwan due to rapid economical and industrial developments, future water price is expected to rise rapidly. How the TFT-LCD industry responds to more costly processing water in order to keep the products competitive is a pressing issue that needs to be resolved. The industry uses the water in different processes that require water of varying degrees of quality, e.g. from tap water to ultra-pure water. Hence, there is much room for improving the whole plant water use efficiency. The objective of this research is to study the optimal water usage strategy without impairing the manufacturing processes or violating the effluent discharge standards. The information collected on a TFT-LCD in southern Taiwan as bases for calculating the total water cost for various water recycle and reuse ratios. After treatment in a conventional wastewater treatment plant, the processing wastewater can be reused as cooling water. The results obtained show that the tendency of cost increase for treating more wastewater is similar to those published in literature. The wastewater treatment plant effluent recycled water must be further treated in a more costly advanced water treatment system to be reused as processing water. The cost analysis results show that the total cost for treating the recycled water is very at the extremely low level of water recycle rate. With increasing recycle rate, the total treatment cost decreases. When the water recycle rate reaches an optimum level, the total cost becomes the lowest; it then increases versus the water recycle rate with the water recycle rate above this optimum recycle rate. For the LCD plant selected for this study, the optimum water recycle rate is 50%. However, this plant is implementing a 70.5% water recycle rate because of managerial considerations but at a loss of NT$ 22.7 million (US$0.758 million) annually. Hence, the best strategy to recycle is recycle water in the LCD plant is to implement the optimum water recycle that will yield the most cost-effective result. This requires the inclusion of water recycle as an integrated part of the whole LCD plant design so that water recycle ratio based on legal and managerial considerations match the recycle ration based on cost-effectiveness considerations.


Keywords: TFT-LCD industry, water recycle, optimal water usage strategy

 

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