2007 Annual Report
1a.Objectives (from AD-416)
(1) Provide baseline data to evaluate the long-term effects of irrigation with treated wastewater; (2) Understand proceses that govern the fate and transport of emerging contaminants, pathogens and nutrients found in treated wastewater used for irrigation; and (3) Develop guidelines for the safe reuse of treated wastewater for irrigation.
1b.Approach (from AD-416)
Sites will be determined where wastewater application has occurred. Soil samples will be taken and analyzed for nutrients, pathogens, and emerging contaminants. Distribution of nutrients, pathogens, and emerging contaminants will be used to determine which constituents may be accumulating in soils for further investigations. Using a combination of lab, column and lysimeter studies fate and transport parameters will be determined for the identified constituents. Concurrently, a series of laboratory and field experiments will be conducted to determine the persistence of pathogens and emerging contaminants in delivery systems. Removal and transformations of nutrients and emerging contaminants as well as pathogen regrowth will be measured throughout the systems. Results and data will be used to identify problems inherent in wastewater irrigation. Constituents that pose a potential environmental risk will be identified and the fate and transport parameters developed will be used to formulate potential management options that could reduce potential environmental degradation. Formerly 5347-13320-001-00D (12/06).
Soil lysimeters have been installed in a Maricopa City, AZ Park for monitoring fate and transport of emerging contaminants and microbial constituents found in treated effluent used for irrigation. The lysimeters are located adjacent to a playing field in a public park where effluent is the sole source of irrigation. The lysimeters have been in place for nearly one year. Leachate has been collected from the bottom of the lysimeters and analyzed for human drugs, hormones and pathogens. Currently no constituents of interest have been isolated from the leachate. Another series of lysimeters irrigated with treated effluent in a temperate climate have also been monitored for three years with no detection of targeted emerging contaminants in the collected leachate. Additionally, enteric bacteria have been identified in the water used to irrigate the lysimeters. It is unknown whether the bacteria originate from the birds and fish that inhabit the pond, or from recovery and regrowth of the enterics within the reclaimed water system. E. coli is a diverse bacterial species but relatively few are human pathogens. Collected E. coli isolates were screened using molecular techniques to determine pathogenicity of the bacteria in the irrigation water. To date, no human pathogens have been identified among the E. coli isolated from the irrigation water.
Constructed wetlands are potentially an important means of treating sewage effluent before release to surface water bodies. The Trés Rios constructed wetland at the Phoenix, Arizona 91st Avenue Sewage Wastewater Treatment Plant experienced a failure of the bulrush population in the wetland. The Bureau of Reclamation has funded a study to evaluate chemical and biological conditions that may have lead to the decline of the plant population of the wetland. Results obtained from three years of study of the H1 basin of the Tres Rios demonstration wetland indicate that the vegetation is exposed to no single stressor that would lead to the loss of vegetation that has been documented. However, it does appear that a combination of factors are converging which have led to the observed phenomenon. First, the nitrogen loading rate into the wetland is very low and could be limiting growth. Concurrent to nutrient deficiencies, measurement of photosynthesis rates indicates a midday depression in photosynthesis indicative of water stress during periods of high evaporative demand. The combination of these stresses appears to be the cause of the browning and die off of vegetation observed in the early summer. Results from this research have been provided to the Bureau of Reclamation and the City of Phoenix to provide guidance in the planning of the full scale project.
Water and nutrient stress in constructed treatment wetlands leading to vegetation die-off.
The Trés Rios constructed wetland was built to determine the feasibility of using a treatment wetland to meet discharge requirements from the 91st Avenue Sewage Wastewater Treatment Plant in Phoenix, Arizona. Three years after construction, the wetland experienced an unexpected failure of the emergent vegetation. Scientists from the US Arid Land Agricultural Research Center conducted a series of monitoring experiments to determine the cause of the die-off. Results obtained indicate that the vegetation experienced both water and nutrient stress which resulted in the die-off. Research results are being used by Bureau of Reclamation and the City of Phoenix to assist in planning of the full scale treatment project.
This accomplishment directly contributes to the accomplishment of National Program #211, Water Availability and Watershed Management, Problem Area Improved Irrigation and Cropping for Reuse of Degraded Waters
5.Significant Activities that Support Special Target Populations
|Number of non-peer reviewed presentations and proceedings||7|
|Number of newspaper articles and other presentations for non-science audiences||7|