Development of a Method for Evaluating Sequence of Water Use to Maximize Benefit of Treatment and Minimize Impact to the Environment
* Given that microfiltration (MF)/reverse osmosis (RO) is capable of treating secondary waste water for infiltration into the drinking aquifer, can the process be optimized so that the concentrate will be acceptable for irrigation of crops?
Need and Benefit
Many communities in the Western United States are experiencing conflict between water uses. Due to population growth, periodic drought, and contamination of ground water, many areas must choose between environmental requirements and municipal and industrial water needs. Water reuse is becoming an accepted option for landscaping and industrial needs, but it is still questionable whether it is safe for human consumption, food crops, or for environmental needs. Since reuse water generally comes from municipal wastewater sources, it is likely to contain human pathogens, pharmaceuticals, and other endocrine- system-disrupting chemicals. The concentrations of these components in municipal wastewater would be more harmful to an aquatic environment than to humans. Pathogenic organisms must be destroyed before waste water is used on food crops.
The WateReuse foundation has funded a study of the rejection, by RO membrane, of a wide variety of emerging contaminants and endocrine disrupting chemicals. The study, by Jorge Drewes of Colorado School of Mines, that began in the fall of 2002 is now complete. He has since tested the performance of several membranes with a variety of trace organics and found that their rejection depends on the membrane material, hydraulics of the system, and the matrix in which they are dissolved. Rejection also can change over time with fouling of the membrane surface. The results do not indicate that municipal wastewater treated with RO, without further treatment without further oxidative treatment, would make suitable habitat for aquatic life. Yet, communities with limited supplies will continue to seek ways to get the most from the water they have.
The current state of the art in wastewater treatment is biological digestion followed by ultrafiltration (UF) and RO. This process is used at Waterfactory 21 and the Scottsdale Water Campus--the two premier water reuse facilities in the world. However, their product goes into aquifer storage for a significant number of years. Other communities such as Big Bear, California, Gallup, New Mexico, Payson, Arizona and McAllen, Texas are considering using the treated water for some more immediate use--either for the environment, irrigating food crops, or direct potable use. It is imperative that we determine how well post oxidation of the RO effluent destroys remaining pharmaceuticals and other organic chemicals. Also, the concentrate stream will have a higher concentration of these chemicals. What treatment is required to make the concentrate safe for irrigation uses? Given that both streams may need to be treated, is it better to oxidize the feedwater?
Reclamation was given the responsibility to oversee water reuse projects through Title XVI. Funding this research will enable reuse project planners to configure their processes correctly with the view of keeping both the concentrate and the desalted streams useable.
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