Location: Water Management and Conservation Research
2022 Annual Report
Objectives
The long-term objective of this project is to provide science based data to ensure that treated municipal wastewater used for irrigation poses minimal threat to people and the environment. Specifically, during the next five years the project will focus on the following objectives.
Objective 1: Determine the processes that govern the environmental fate and transport of emerging contaminants and other constituents found in treated wastewater used for irrigation to provide a research basis for potential regulation of these constituents.
Objective 2: Develop and optimize low input treatment systems to reduce emerging
contaminants and nutrients found in degraded waters to increase water resources used for food production.
Approach
Objective 1 is a combination of monitoring of treated wastewater effluent for emerging contaminants (ECs) and research to investigate the potential for organic sorbents to sequester emerging contaminants in the environment. The mass of pharmaceuticals taken up by crops irrigated with treated municipal wastewater depends on the concentration of the pharmaceutical at the soil-root interface and the volume of water needed to meet plant metabolic needs. The concentration of pharmaceuticals at the root is determined by initial concentration applied and soil processes that remove the pharmaceutical from the soil solution.
Evaluating Temporal Patterns of ECs: Pharmaceutical concentration in sewage effluent will be measured on three different time scales from five different regions of the country (arid, semi-arid, humid continental, humid sub-tropical, tropical) to characterize the concentration of ECs found in reclaimed water. One sewage treatment plant from each region will be chosen for sampling. Treatment plants of similar size with similar treatment trains will be selected and sampling will consist of four high intensity sample periods lasting one week each in winter, spring, summer, and fall. Samples will be time averaged composite samples with equal aliquots collected every 30 minutes.
Evaluating the potential for organic residues to remove carbamazepine from irrigation water: Previous research has shown that organic materials can act as sorbents to remove trace organics, however, most of this research is limited to pesticides and industrial pollutants. The sequestration of these compounds by organics has typically been measured on systems where the contaminant is present at part per million levels (ppm), while ECs are typically found at part per billion (ppb) levels or less in irrigation water. It is hypothesized that sub ppm levels of ECs found in irrigation water can be effectively and economically removed from the water through the use of sorbents derived from waste products. Raw waste products to be tested will include post-harvest plant residues, biochars derived from plant residues, and organic wastes. Effective removal will be governed by overall sorbate characteristics, which include sorption kinetics, total sorption potential, and effective sorbent life span.
Objective 2 is a laboratory scale design and engineering endeavor to develop viable treatment practices to remove EC’s from irrigation water prior to plant uptake. Candidate sorbents will be evaluated for EC removal efficacy from irrigation water. It is hypothesized that through proper placement and treatment of organic plant residues the soil solution concentration of ECs can be reduced. Candidate sorbents will be evaluated in both media filters and as soil amendments concentrated where water application occurs to evaluate EC removal potential. Evaluation of field treatment options will use three different removal options: 1) Use of organic amendments as filter media; 2) Use of organic amendments to increase overall soil sorptive capacity; and, 3) Selective placement of organic amendments to intercept irrigation water prior to soil application.
Progress Report
This is the final report for project 2020-13000-004-000D, The Use of Treated Municipal Wastewater as a Source of New Water for Irrigation, which has been replaced by new project 2020-13000-005-000D, Increased Water Security through Safe Reuse of Reclaimed Water. For additional information, please review the new project report.
Research related to completing Objective 1 was very limited due to COVID-19-related travel restrictions. A very limited number of samples were collected and analyzed from a wastewater treatment facility in Oklahoma. Travel for collecting these samples was authorized because of an existing financial agreement that made the sampling mission critical. Samples were collected in collaboration with the city of Norman, Oklahoma, to evaluate the effectiveness of advanced treatment options to prepare for indirect potable reuse. Samples were collected for three days prior to advanced treatment and three days after advanced treatment. Samples will be analyzed for a suite of 80 pharmaceutical compounds to determine process efficacy. Samples are currently being analyzed and advanced treatment systems will be evaluated based on removal efficiency.
Research in support of Objective 2 has continued. Biochar produced from the pyrolysis of two agricultural waste products: cotton gin waste (pyrolyzed for 2 h at 700 C, CG700) and walnut shells (pyrolyzed for 2 h at 800 C, WS800) to better understand their potential applications for water quality improvement. Each biochar was characterized for specific surface area, changes in morphology, surface functional groups, and the pH point of zero charge. The higher temperature used to produce WS800 led to increases in the specific surface area and dehydration of the biochar. Pyrolysis led to destruction of acidic functional groups and an increase in ash content, resulting in the production of hydrophobic alkaline biochars with pH values of 9.85 and 10.93 for WS800 and CG700, respectively. Zeta potential measurements demonstrated that WS800 and CG700 biochars are negatively charged, suggesting suitable applications for the removal of cationic contaminants from the environment. Overall, results demonstrated that biochars obtained from agricultural waste have the potential to be effective sorbents for decontamination of wastewater and soil.
Accomplishments
1. Removing pharmaceutical contaminants from wastewater. Current sewage treatment processes are not designed to remove low level concentrations of pharmaceuticals. ARS scientists in Maricopa, Arizona, manufactured from magnesium oxide and copper a new porous nanomaterial that is a good catalyst for removing salicylic acid and tetracycline. The catalyst removed all salicylic acid and tetracycline from solution within 15 and 30 minutes, respectively, and maintained reactivity for more than five reaction cycles. Additionally, degradation resulted in no untoward byproducts and the catalyst was conserved. The new catalyst has potential for use in current wastewater treatment plants to remove trace organics prior to environmental discharge.
2. Growing corn and sugar beet with feedlot effluent, air injection, and subsurface drip irrigation system in Western Nebraska. Effluent from feedlots contain high concentrations of dissolved organic carbon, which when released to the soil leads to rapid mineralization and depletion of soil oxygen that can lead to stunted root growth and loss of yield. ARS scientists in Maricopa, Arizona, evaluated a low energy air injection method to determine if additional oxygen in feedlot wastewater could prevent yield loss in corn and sugar beets. The use of subsurface drip irrigation air injection increased corn yield by 5.5% and 9.2% in 2019 and 2021, respectively. In addition, corn water use efficiency was significantly increased in 2021. Sugar beet yields were not affected by air injection; however, sugar beet water use efficiency was significantly increased in 2019. Overall air injection into feedlot wastewater used for irrigation increased both soil oxygen status and corn yield in Western Nebraska.
