Wastewater Reuse

Approximately 1.2 billion people around the world live in areas of physical water scarcity. This could increase to half of the world’s population by 2030 and could displace 24 to 700 million people unless steps are taken to ensure adequate water supply. Water scarcity is an escalating issue within the United States, specifically in Western inland states with arid climates. This scarcity is encouraging communities to investigate tertiary level municipal wastewater treatment, allowing for reuse of wastewater. Unfortunately, wastewater contains numerous contaminants that are not regulated by the Environmental Protection Agency (EPA) under the Safe Drinking Water Act (SDWA). Many of these contaminants are endocrine disrupting compounds (EDCs). According to the European Union Commission, an endocrine disruptor is an exogenous substance that causes adverse health effects in an intact organism, or its progeny, in consequence to the induced changes in endocrine functions. Many EDCs are not completely removed by standard secondary wastewater treatment methods. With the growing demand for potable water, as well as water for irrigation and agricultural purposes, communities are having to evaluate the potential health risks due to EDCs and other unregulated compounds. The Woo-Pig-Sewage team selected one unregulated contaminant, chlorpyrifos (CLP), to test. CLP is an organophosphate insecticide that is commonly used residentially and commercially. CLP has a long term impact as a cholinesterase inhibitor in humans. Using traditional biological methods, CLP, as well as other pesticides, are nearly impossible to remove. CLP is on the Fourth Unregulated Contaminant Monitoring Rule list produced by the EPA to provide a basis for future regulation. A bench scale unit utilizing ozone treatment (O3), ultraviolet radiation (UV), and granular activated carbon (GAC) was constructed to remove this contaminant from doped nanopure water. Ultimately, the selected technologies will be able to treat secondary wastewater effluent from the wastewater treatment plant (WWTP) in Tucumcari, New Mexico for direct or indirect aquifer reintroduction. Direct aquifer reintroduction would involve injection of water to the existing aquifer, while indirect aquifer introduction would consist of introducing treated effluent to an existing canal system. An oxidation process paired with UV and GAC filtration can be utilized to remove EDCs such as CLP and other unregulated contaminants from wastewater. O3 is extremely effective at oxidizing bacteria as well as other organic molecules. UV is also a commonly used method to degrade organic compounds and is currently being used at the WWTP in Tucumcari, New Mexico and in Fayetteville, Arkansas. GAC is utilized to remove trace amounts of contaminants from wastewater streams, usually as a final treatment before the water is reintroduced to the environment. The WWTP in Rio Rancho, New Mexico currently plans to utilize GAC filtration in this manner. The Woo-Pig-Sewage team performed experiments to determine if the combination of O3, UV, and GAC could reduce CLP to a concentration below the minimum detection limit of 0.001 ppm. To test the effectiveness of the bench scale, caffeine was used as an organic tracer. Bench scale results indicate that the proposed system is effective in the removal of caffeine and CLP from doped water samples. Caffeine concentrations were reduced to below the minimum detection limit of 0.05 ppm for samples with initial concentrations ranging from 0.1 ppm to 10 ppm. CLP was reduced to below the minimum detection limit of 0.001 ppm from and initial concentration of 0.1 ppm. An industrial scale process was sized based on treating secondary effluent from the WWTP in Tucumcari, NM. The total cost was determined to be an additional $2.31 per 1000 gallons, assuming 0% grant funding and a 6% commercial loan. This estimate brings the total cost to $4.95 per 1000 gallons for the existing treatment paired with the proposed system. While this adds a significant cost to the existing treatment at the WWTP in Tucumcari, plants with larger flow rates would see significantly less of an increase in the total cost per 1000 gallons. This can be seen from the comparison of the 144,000 gallon per day (gpd) system with existing UV treatment and the 300,000 gpd Tucumcari system also utilizing UV treatment. The 144,000 gpd system was estimated to cost about 60% more per 1000 gallons. However, if the Tucumcari WWTP is awarded a grant to cover 100% of the Fixed Capital Investment (FCI), the proposed system would only increase the cost per 1000 gallons by 38%. If the EPA determines that EDCs such as CLP must be removed from the effluent of WWTPs, a process such as the one proposed by the Woo-Pig-Sewage team will be necessary