Arizona Researchers Address Wastewater Treatment and Water Reuse

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The Water Resources Research Act, Section 104(b), established a program for funding water research through designated Water Resources Research Institutes. In Arizona, the Water Resources Research Center awards three to five research grants annually, of approximately $10,000 each, for the best project proposals received from investigators at the University of Arizona, Arizona State University and Northern Arizona University. The following projects, funded for the project year 2012-13, addressed issues associated with wastewater treatment and water reuse.

For the research project titled “Fate of Emerging Nanoparticle Contaminants during Aquifer Recharge with Treated Wastewater”, investigators Drs. Reyes Sierra and James Field studied the removal of engineered nanoparticles from wastewater. Effluent discharges from municipal and industrial wastewater treatment plants are important sources of nanoparticles in the environment. In addition to consumer products (e.g. sunscreen, cosmetics, medicines, printing ink and computer chips), nanoparticles are used in industrial processes such as the manufacturing of semiconductors. Laboratory studies offer compelling evidence that engineered nanoparticles can be toxic to mammalian cells and other ecologically important species.

Artificial recharge of aquifers with treated wastewater potentially would allow nanoparticles in wastewater to reach groundwater used for drinking water supply. The purpose of this study was to determine the extent to which soil-aquifer treatment is effective in removing nanoparticles from recharged wastewater effluent. Soil aquifer treatment refers to processes that occur during artificial recharge of treated wastewater. As the effluent moves through the soil and aquifer, physical, chemical and biological processes further reduce contaminants in the water. This project provided quantitative data on the removal of nanoparticles as well as qualitative information on the processes responsible for their removal. Researchers conducted experiments using a saturated sand media with and without selected organic contaminants. Results indicated that the composition of the treated water has a strong impact on the transport of nanoparticles.

Drs. Channah Rock and Leif Abrell are the principal investigators for the research project titled “Does Increasing Solids Retention Time in the Wastewater Treatment Process Affect the Persistence of Antibiotic Resistance Genes?” According to the Centers for Disease Control and Prevention, antibiotic resistance is one of the world’s most pressing public health threats, responsible for tens of thousands of deaths in the United States. Antibiotic resistance may be associated with the exposure of bacteria to trace antibiotics in the environment.
Increased solid retention time during wastewater treatment has been correlated with reductions in trace antibiotics. The rapid bacterial growth and high antibiotic concentrations during retention of solids, however, may provide ideal conditions for developing antibiotic resistance. This research assessed the effects of varying solid retention times in full-scale activated sludge processes on both trace antibiotics and antibiotic resistance. Shorter solid retention times (ranging from one to six days) appeared to be the more effective at mitigating antibiotic resistance when compared to retention times of nine to 25 days.

Drs. David Quanrud, Robert Arnold, Eduardo Saez and Shane A. Snyder collaborated on the project titled “Toxicity of Emerging Contaminants in an Effluent Dependent Stream: the Role of Suspended Solids and Sediments.” This research evaluated the toxicity and endocrine disruption activity of trace organic contaminants found in the effluent dependent Santa Cruz River, downstream of wastewater treatment plants in Tucson, Arizona. Many household substances contain chemicals that persist after conventional wastewater treatment. Some of these are considered contaminants of emerging concern and may have endocrine disrupting properties. Because of their chemical characteristics, many of these contaminants accumulate with solids.

Thus, suspended solids in effluent discharge are potentially significant sources of emergent contaminants. This project assessed endocrine disruption activity in liquid-phase wastewater effluent, suspended solids and riverbed sediments as a function of downstream travel distance. Liquid-phase and suspended solid concentrations of estrogenic activity decreased by more than 95 percent along the 23-mile river segment. The study also provided much needed baseline data on the Santa Cruz River prior to the 2015 completion of upgrades to two Pima County municipal wastewater treatment facilities, which are expected to substantially improve effluent quality and river health.

Dr. Shane A. Snyder is the principal investigator for the project titled “Disinfection By-product Formation from Water Reuse Practices.” This project, funded in 2011 and extended to 2013, recently reported findings. Interest in direct potable reuse—a system that connects highly treated recycled water directly to the drinking water network—is growing in the arid Southwest. Some technologies commonly used to purify wastewater to potable standards can produce potentially harmful disinfection byproducts from reactions with common contaminants such as iodine and organic nitrogen. This project characterized and evaluated the potential for certain disinfection byproducts to form in actual waters under various treatment scenarios. Effluent samples were taken from the treatment plants at Roger Road and Ina Road in Tucson, Arizona, and from groundwater recharged at the Sweetwater Recharge Facility. Most trace organic compounds decreased when wastewater was treated by ozonation; however, the formation of a specific disinfection byproduct—NDMA—was at times significant. Infiltration of the water before the experimental treatments clearly improved water quality by reducing levels of precursor contaminants.