Arizona Researchers Address Water Quality, Reuse and Management

Return to AWR Fall 2014

by Mary Ann Capehart, WRRC Graduate Outreach Assistant

Section 104(b) of the Water Resources Research Act, first passed in 1964, established a program for funding water research through designated Water Resources Research Institutes nationwide. In Arizona, the Water Resources Research Center has for many years awarded three to five research grants annually, of approximately $10,000 each. Investigators at the University of Arizona, Arizona State University and Northern Arizona University are eligible for this funding. The following projects, awarded for the project year 2013-14, addressed issues associated with water quality, data collection and the use of hydrological modeling in water resource management.

Extraction Methods for Engineered Nanoparticles from Aqueous Environmental Samples

This research project is a first step toward answering questions about the presence of nanoparticles in water. Nanoparticles are a class of nanomaterials sized between 1 and 100 billionth (10-9) of a meter (1-100 nanometers) in at least one dimension. To understand this scale, consider that a human hair is roughly 75,000 nanometers in diameter. Like larger particles, nanoparticles may be released into the environment during manufacturing, use, delivery or disposal. Nanomaterials, however, have the potential to remain in the environment for longer periods and may be transported over greater distances than their macro-scale counterparts. A multitude of consumer products currently use nanomaterials, and new applications of nanotechnology are increasing. Washed into sewer systems and surface waters, these materials are raising concerns about their effects on environmental and human health. Thus, an effective method for their detection and characterization in natural water bodies or wastewater is urgently needed.

To identify an efficient method for accomplishing this, investigators Paul Westerhoff and Yu Yang of Arizona State University assessed the efficiency of several methods for extracting nanoparticles from a range of different solutions—ultra-pure water, and samples from the Salt River, the Verde River, influent and effluent from a wastewater treatment plant, Saguaro Lake, and Tempe Canal. The team used nano silver and nano gold to examine the extraction efficiency of each method in ultra-pure water, because of the common use of these materials in consumer products and concerns about their toxicity. Metallic nanomaterials exhibit chronic toxicity in biological systems.
The researchers then extracted nanomaterials from other water samples using the most efficient method and characterized the extracted materials with a combination of microscopy and spectroscopy. The most abundant nanoparticles identified were Silicon and Titanium containing particles with diameter in the range of 4-99 nm. Other nanoparticles, which ranged in size from 30-65 nm, contained major elements, including calcium, magnesium, aluminum, iron, oxygen, sulfur, carbon, and chloride. The researchers found that generally, “cloud point extraction” coupled with “transmission electron microscopy” and “energy dispersive X-ray spectroscopy” was an effective tool for extracting and characterizing nanomaterials in environmental water.

Do Simple Carbon Additions Reduce Resistance to Antibiotics in Environmental Bacteria?

In Arizona, the use of recycled wastewater is increasing to augment limited potable water supplies. Recycled water currently sustains agricultural production and riparian environments. The use of municipal biosolids on agricultural soils has also increased. Suspended in both of these resource streams are trace concentrations of commercially produced antibiotics, which add to antibiotics that naturally occur in soil microbe populations. The concern of environmentalists and public health advocates is that microbe populations will evolve a resistance to these trace antibiotics. They fear that in potential instances of human exposure to these resistant microbes, the treatment of human infections by various antibiotics will be rendered ineffective.

University of Arizona researchers Jean E. McLain and Channah Rock’s research project examines the hypothesis that long-term application of recycled water and biosolids onto agricultural and riparian area soils abates the response of microbes to develop resistance to antibiotics. This hypothesis originated from a multi-year study examining the effects of the long-term (20-plus years) application of recycled municipal wastewater and biosolids on the development of antibiotic resistance in soils. The study found evidence that the hypothesis is correct. No increase in antibiotic resistance in environmental bacteria has been observed, and there was a marked decrease in multiple-antibiotic resistance in sites receiving long-term recycled water and biosolids application. A plausible explanation is that continual application of recycled water and biosolids increase organic carbon reserves in soils thereby decreasing competition between microbes. This in turn decreases the necessity for antibiotic production on the part of soil microbes. Study results may help to alleviate some concerns that environmental and public health advocates have regarding the use of recycled water and biosolids to augment water and soil carbon supplies in Arizona.

Sequential Advanced Oxidation and Soil-Aquifer Treatment for Management of Trace Organics in Treated Wastewater

As water supplies are threatened by the impacts of drought, climate change and the rising demand for potable water by growing populations in the arid Southwest, communities will come to rely on reclaimed water as a source of potable water. The transformation of reclaimed water to drinking water calls for a high level of water treatment. Many of the trace chemicals that enter municipal wastewater are only partially removed during conventional wastewater treatment. An assortment of pharmaceuticals, hormones, disinfection by-products and personal care products, though existing at sub-part-per-billion concentrations in water, may have negative ecological consequences. Some of these trace organic contaminants, like the unregulated substance NDMA—a byproduct of drinking water disinfection or various industrial processes—are known to cause cancer in laboratory animals.

A research project led by A. Eduardo Sáez and David Quanrud examined a potential synergy between two treatment methods coupled for the effective removal of trace organic compounds that routinely survive conventional wastewater treatment. Advanced oxidation treatment (UV/peroxide) followed by soil infiltration treatment (simulated soil-aquifer treatment) were found to be effective. Advanced oxidation processes, using solar light as the source of UV radiation, generate hydroxyl radicals that oxidize the vast majority of trace organic compounds found in treated wastewater. The infiltration of the water in the soil also removes certain trace organics due to their transformation by microorganisms living in the soil. This combination of advanced oxidation with the natural processes of soil-aquifer treatment is likely to reduce health risks for communities and species in the environment at a cost much lower than an engineered solution alone could produce.

Discrimination-Inference to Reduce Expected Cost Technique (DIRECT): A new framework for water management and stakeholder negotiation

Hydrologists and other natural scientists play an important role in supporting decisions that affect people and the environment. Environmental systems are complex and the behavior of water in these systems can be difficult to predict accurately. Given this complexity, design of data collection should be optimized to allow hydrologists to make the best predictions of interest to decision makers and other stakeholders. Scientists can no longer develop a simplified mathematical model of a natural system and suggest that predictions from this model represent known outcomes. Rather, scientists must not only make their best predictions, but also provide quantitative measures of the uncertainty of these predictions. This allows decision makers to consider the full range of possible outcomes, with associated likelihoods of occurrence, when managing water resources.

A research project of Paul A. Ferre and colleagues combined tools in hydrologic modeling with a new approach to monitoring network design to address these challenges. This collection of tools is named Multi-Model Analysis with Discriminatory Data Collection (MMA-DDC). Effort during this project was devoted to developing a solid theoretical and mathematical basis for the Data Discrimination Index that underlies MMA-DDC and developing a modular code based on this foundation. This code was applied to academic studies for the optimal design of large-scale vadose zone field studies and practical studies for water-rights acquisition to augment baseflow. Finally, it was used in the selection of monitoring points to determine whether to pursue active or passive treatment of a contaminant plume. These applications demonstrated that MMA-DDC allows stakeholders to define their priorities, hydrologists to use these priorities to target improved knowledge through data collection, and decision makers to make direct use of hydrologic models for risk-based decision making.