Location: Water Management and Conservation Research
2023 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.
Sub-objective 1.A: Determine the effect of temperature on the sorption, fate, and transport of pharmaceuticals in soil.
Sub-objective 1.B: Determine the effects of long-term wastewater irrigation on soil contaminant concentration and the soil microbiome.
Sub-objective 1.C: Optimize removal of pharmaceuticals from water.
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 will seek to Increase water supplies available for irrigation and managed aquifer recharge through safely reusing treated wastewater. The effect of temperature and season on the environmental fate and transport of contaminants of emerging concern (CEC) found in reclaimed wastewater will be characterized and quantified. Ten different pharmaceuticals that have a range of pKa’s from (4.0 – 16.0) will be evaluated in the lab by batch sorption and column flow through experiments using soils from the Southwest US. Experiments will be conducted at 10° C, 25° C, and 40° C. Pharmaceutical mobility will be evaluated and compared to seasonal soil temperatures to determine seasonal variability in soil transport. A set of paired stormwater recharge basins, one that receives wastewater inputs and one that does not, will be sampled for pharmaceutical analysis. Results from lab experiments and the paired basins will be used to model the potential for stormwater retention basins to contaminate groundwater with pharmaceuticals found in the wastewater used for irrigation. These results will be used to provide management guidance for stormwater retention basins. Finally, biochar pyrolyzed from walnut shells and cotton gin waste will be evaluated as a treatment method for removing pharmaceuticals from wastewater. Biochar pretreatments will include untreated, acid treated, and base treated prior to pyrolysis. Lab scale columns will be constructed and water containing pharmaceuticals will be passed through biochar filter columns. Removal efficiency and capacity will be calculated, and sorption mechanisms elucidated.
Objective 2 Will be a modeling exercise to determine the potential for using reclaimed wastewater as a supplemental irrigation source in rainfed agricultural systems. The volume of produced wastewater in regions of the Midwest will be spatially matched to potential crop needs. Crop irrigation needs will be modeled using historical weather data and then spatially matched to wastewater availability. Results will be used to determine potential yield loss related to reduced rainfall due to short term spatial and temporal drought. Yield recovery will be related to available water and distance water needs to be transported.
Progress Report
This report documents progress for project 2020-13000-005-000D, “Increased Water Security through Safe Reuse of Reclaimed Water”, which began in January 2022.
In support of Sub-objective 1A, sorption experiments were continued for more pharmaceuticals at different temperatures. Overall, sorption of eight pharmaceuticals to soil have been evaluated at temperatures representative of winter, spring/fall, and summer in the low desert regions of the Southwestern United States. Generally, as temperatures increase sorption decreases. Results indicate that the optimal use of treated wastewater is dependent on season. When temperatures are high, wastewater is better suited for irrigation. However, when temperatures are low, mobility is reduced and the use of treated municipal wastewater for groundwater recharge is acceptable.
For Sub-objective 1B, soil samples have been collected from a non-wastewater irrigated infiltration basin and are in the process of being extracted for analysis of pharmaceuticals and genomes. A wastewater irrigated infiltration basin has been identified. Permission to access the wastewater irrigated basin has been approved and sampling is scheduled to occur in the first quarter of FY 2024.
In support of Sub-objective 1C, biochars produced from cotton gin waste and walnut shells have been evaluated and for removal of pharmaceuticals from water. A series of experiments were conducted to determine the effect of treatment prior to pyrolysis and after pyrolysis on sorption potential. It was found the pretreatment of feedstock with acid and base prior to pyrolysis resulted in a five-fold increase of surface area. In addition, it was found that a 24-hour water rinse of biochar’s after pyrolysis resulted in a ten-fold increase in surface area. Results are being used to optimize removal of pharmaceuticals from water in low input flow through systems.
Progress for Objective 2, included a crop growth model being used to determine critical growth stages in Maize when water deficits can lead to significant reduction in overall yield. The model has been evaluated using simulated weather data with micro droughts lasting 7-21 days. Results indicate that there are several critical growth stages where temporary water stress significantly reduced yield. Historical weather data has been identified for several counties in Iowa that will be used for input into the crop growth model to evaluate potential yield loss due to short term water stress.
Accomplishments
1. Heterogeneous photo-fenton-like degradation of emerging pharmaceutical contaminants in wastewater using Cu-doped MgO Nanoparticles. Current sewage treatment processes are not designed to remove low level concentrations of pharmaceuticals. A new porous nanomaterial made from magnesium oxide with up to 10% copper was manufactured. The novel nanomaterial was shown to be a good catalyst for removing salicylic acid and tetracycline in the presence of UV light and hydrogen peroxide. The catalyst was found to be able to remove all salicylic acid and tetracycline from solution within 15 and 30 minutes, respectively, and was found to maintain reactivity for more than five reaction cycles. Additionally, degradation resulted in no untoward byproducts and the catalyst was conserved. The new catalyst has the potential for use in current wastewater treatment plants to remove trace organics prior to environmental discharge.
2. Experiments using cotton gin waste and walnut shell-derived biochar as low-cost ways to remove pharmaceuticals from aqueous solutions. Biochar produced from cotton gin waste and walnut shells was evaluated by ARS researchers in Maricopa, Arizona, and found to remove four pharmaceuticals, acetaminophen (ACT), sulfapyridine (SPY), ibuprofen (IBP), and docusate (DCT), from aqueous solution. Fixed-bed column experiments were performed to determine the difference in removal efficiency between biochars and elucidate the effects of biochar properties on the adsorption capacity for the pharmaceuticals of interest. Results showed that cotton gin biochar produced at 700 C had a greater affinity for removing DCT (99%) and IBP (50%), while walnut shell biochar produced at 800 C removed 72% of SPY and 68% of ACT after 24 h. Adsorption was influenced by the solution pH, surface area, net charge, and functional groups of biochar. The mechanisms for removal included pore filling and diffusion, hydrophobic interactions, hydrogen bonding and pi-pi electron donor acceptor interactions. Overall, the results demonstrate that biochar from cotton gin waste and walnut shells could be used as cost-effective, environmentally friendly alternatives to activated carbon for the removal of pharmaceuticals from aqueous solutions.
