Howard Weinberg The University of North Carolina at Chapel Hill
With population growth and recurrent drought conditions in much of the United States and across the world, new uses for reclaimed wastewater must be considered to preserve freshwater quality. Terrestrial application of treated wastewater such as for crop irrigation could simultaneously protect drinking water source quality, by diverting treated waste effluents from sensitive aquatic ecosystems while reducing demand for drinking water. This project will optimize green infrastructure designs including aerobic vegetated sand filtration (VSF) in combination with subsurface flow (SSF) constructed wetlands for removal of chemicals of anthropogenic origin in wastewater and investigate the extent to which residual chemicals in the reclaimed water accumulate in the edible portions of crops irrigated with this type of water. The project will systematically evaluate how changes to the operation of VSF and SSF can optimize trace organic contaminant and pathogen removal to minimize measureable differences between crops irrigated with such reclaimed water and those irrigated with tap water. This will be achieved through two approaches; a laboratory column study that simulates the treatment designs will investigate the combination of different processes and filter substrates for this optimization using a characterized domestic effluent, and the treated water will then be used in a greenhouse to irrigate a variety of crops including potatoes, soybeans, and leafy vegetables selected because of differences in known properties of chemical uptake or rejection alongside controls conventionally grown with tap water. Specifically, we will determine whether crops irrigated with such waters reject the pollutants making them viable for consumption or if the crops uptake the pollutants and, if so, might they be used as an additional remediation tool for wastewater treatment. Changes to the operation of the green infrastructure design process determined from the laboratory study will then be transferred to full-scale operation and the viability of the optimized process towards crop growth evaluated onsite. The project will, therefore, demonstrate whether more widespread use of similar designs and the use of reclaimed water in this manner could be part of a managed approach to pollutant remediation and crop irrigation, thereby saving freshwater for more critical needs.
The project will provide a better understanding of how vegetation and crops respond to the presence of wastewater constituents in their environment. Most wastewater treatment systems are not specifically designed to remove man-made chemicals from the influent waste and so by evaluating the fundamental treatment processes in a laboratory-controlled environment, design can be better optimized to improve treated water quality. Moreover, the project results will show whether wastewater constituents are taken up by the crops (in which case such a process has implications for a remediation technology) or whether the crops are resistant to uptake (in which case a more widespread use of recycled wastewater in crop irrigation can be considered). The use of green infrastructure design for the effective removal of wastewater contaminants at the site of their entry into wastewater has broader impacts on the disbursal of these contaminants throughout the wider environment as is typical in wastewater discharges from centralized wastewater treatment plants. Upgrading such plants to target individual contaminants and prevent their disbursal will likely prove expensive whereas with on-site treatment, cost can be staged and treatment more effectively targeted to individual pollutants. The project will also provide policymakers with valuable information to assist with determining safe operating practices and will help to improve public perception regarding the safe use of reclaimed water.
