Location: Water Management and Conservation Research
2019 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
Progress was made on both objectives, which fall under National Program 211, Water Availability and Watershed Management.
Under Objective 1, quarterly sampling of the Neely wastewater treatment plant in Gilbert, Arizona, was completed in 2018-2019. Two of the four quarterly sampling events at the State College, Pennsylvania, wastewater treatment facility have been completed. Two sampling events were missed due to the government closure. Samples are being analyzed for pharmaceuticals and potential endocrine disruptors. Results will be used to provide input data for human health risk assessment models.
Under Objective 2, biochar produced using guayule and cotton gin waste at different temperatures has been evaluated for pharmaceutical removal potential from water. Using batch sorption techniques, biochar produced from cotton gin waste pyrolyzed at 700 Celsius (C) has been shown to have the highest potential to remove pharmaceuticals from water. Removal potential was linked to total surface area of the biochar and the total charge density of the biochar as affected by solution pH. Currently this biochar is being evaluated for total mass removal potential and removal kinetics. Results will be used to design and evaluate potential removal systems utilizing biochar as a filter media. Biochar produced from guayule bagasse was found to have limited removal potential, which was linked to very low surface area. Future research will be conducted to determine if chemical modification prior to, and during pyrolysis, can increase sorption potential.
Accomplishments
1. Air injected into irrigation water can reduce the uptake of pharmaceuticals into fresh produce. Water scarcity has led to the increasing use of treated municipal wastewater containing low levels of pharmaceuticals for irrigation. ARS researcher in Maricopa, Arizona, showed that increased aeration of irrigation water using an air injection system prior to sub-surface drip irrigation can reduce the fate and uptake of some pharmaceuticals into food crops. Air injection was shown to reduce the concentration of three pharmaceuticals (caffeine, carbamazepine, and gemfibrozil) in the soil and leachate; uptake of caffeine and gemfibrozil into lettuce was lower in the air injection treatments, but carbamazepine uptake was greater in the air injection treatment. Air injection also resulted in changes in the soil microbial community. Air injection may be a useful point of use treatment technology to reduce the environmental availability of pharmaceuticals. Producers and consumers of leafy green vegetables are the primary beneficiaries of this research.
