The constructed wetlands treatment and reuse of cooling tower blowdown water at General Motor's Saturn plant

General Motor's Saturn Plant in Spring Hill, Tennessee began production in 1990. The Saturn Plant produces up to 736,000 gallons per day of air conditioning cooling tower blowdown water which is currently discharged to the sewer system. This investigation performed a theoretical analysis of the alternative management method of treatment of the blowdown water in a constructed wetlands followed by spray irrigation of crops farmed on site by Saturn. The environmental fate and effect of the inorganic pollutants in the blowdown water was determined by comparison of projected water quality with standards promulgated for wastewater irrigation. For the inorganic pollutants in excess of wastewater irrigation water quality standards, the expected degree of treatment in a constructed wetlands was calculated from precipitation and complexation equilibria. The potential for deleterious metal buildup in the crop soils was also calculated. The fate of the organic pollutants in the blowdown water was determined by review of available information and from a correlation with the octanol/water partition coefficient, a predictor of environmental fate. The suitability of site stormwater runoff for use in the system was also assessed.

The investigation concluded that treatment in a constructed wetlands followed by spray irrigation of crops after supplementation with site stormwater runoff is a potentially attractive alternative to managing the blowdown water. The advantages of such a management alternative include reduction of wastewater disposal costs, conservation of water and sewer capacity, improved crop production and demonstrated public relations. The use of site stormwater runoff would also minimize the plant's impact on the environment