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Water
| Reduce water draw-down (per million dollars of standard production value) from local sources (conduits, streams, and aquifers) by more than 10% per year through conservation. |
Water conservation is a general ST corporate goal, but it is an imperative at several STMicroelectronics manufacturing sites where water supplies are scarce or diminishing - Malta, Rancho Bernardo, Phoenix, Catania and Singapore, for example. At a corporate level, ST has substantially cut its use of water, reducing the cubic meters used per million dollars of standard production value from 11,300 m 3 in 1994 to 6,800 m3 in 1999. Overall, 98% of the Decalogue goal was met, with the trend improving towards the end of the year.
Especially for those sites with shortage of fresh water, ST is increasingly concentrating its efforts in developing methods to reuse waste water during several of the manufacturing process steps.
NEW
Continue to reduce water draw-down (for million dollars of added value) by at least 5% per year, through conservation, optimization, recycling. |
| For all manufacturing operations, reach a level of 50% recycled water by end 1997 and 90% by end 1999. |
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Several sites have already installed a backgrinding water recovery system. This consists of an ultra filtration system for silicon wafer saw water. The water containing silicon particles is collected and stored in a common tank and is transferred by pump to the filters. The cleaned water is then sent back to the DI plant for re-use. |
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In our Singapore (Ang Mo Kio) plant, for example, nearly 100% of backgrinding water is recovered with a savings of 10m3 per hour : a total capital savings of $284,000 and overall savings of $263,000 annually with a payback in 15 months. |
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In Malta, large volumes of water are used during silicon wafer cutting. In the slicing process, silicon dust is too fine to be captured by traditional filters. The site installed a microfiltration unit to remove the fine particles and the water was then further purified by passage through ion-exchange resin columns. Water is then sufficiently clean to be recycled for operations requiring extremely high purity water. As a result, the use of city water was reduced by some 13,000m3 per year. |
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The Malta site also recycles waste brine which is discharged by the plant's Electrodialysis Reverse (EDR) water purification system. EDR is a system in which a potential difference is applied to remove 80% of salts from the mains water. The concentrate waste is filtered and chlorinated and is suitable for non-potable use in toilet flushing, for instance. Through this means, city water consumption dropped by a further 6,500m3. |
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In 1998, the Malta site made a major effort to recycle waste water from its electroplating operations. A new design using ion exchange resins recovers metals from electroplating water. This is followed by a reverse osmosis system to further purify the water. |
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Other water conservation strategies set up by Malta include the installation of a rainwater capture and recycling system. In 1999, the facility reduced its consumption from city mains from 183,000m3 for the year down to 48,000m3 - a remarkable reduction of 73%. |
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ST's manufacturing plant in Carrollton participated in a third-party water consumption evaluation of its manufacturing process with International SEMATECH and will begin to implement process changes in the year 2000. |
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