CONTINUING TO OFFSET WATER USE IN SILICON WAFER MANUFACTURING – AN UPDATE

This paper reports the results achieved and lessons learned from 6 years of successful water use consumption reduction at various MEMC Electronic Materials, Inc., manufacturing facilities. MEMC obtained water cost savings and significantly increased production without increasing water supply demand or expanding wastewater treatment facilities using a utilities-driven water reuse approach. Specifically, the Spartanburg plant (which makes silicon wafers for the microelectronics industry) used water balance techniques to identify opportunities for water reuse and achieved a water reuse rate of 23 percent. Over the 5-year period of operation, the Spartanburg water reuse system avoided 209,600 in purchased water cost. MEMC invested a total of 410,500 in this system between 1993 and 1998. More importantly, water reuse enabled MEMC to avoid an expansion of wastewater treatment facilities estimated to cost 1.2 million in 1992 dollars. Although some difficulties were experienced (conductivity upsets, biofouling, etc.), lessons were learned and conclusions were drawn which may help future designers.As illustrated above, paybacks typically exceed 5 years or more for utilities-based capitalintensive water reuse projects. These projects are justified more by capital avoidance than by savings return on investment. As margins on silicon wafers have decreased, financial justification for utilities-based capital projects have become more difficult. MEMC has been forced to shift its water reduction efforts from a more capital-intensive utilities-focus to a more culture-based water conservation focus by establishing goals for water use efficiency and metrics for water use tracking. This has blended well with the management systems adopted for ISO 14001 certification and has resulted in a 32.4% reduction in water usage company-wide since the beginning of 1999.