Nitrogen and Phosphorus Remediation in Mesocosm Floating Treatment Wetlands receiving Municipal and Aquacultural Wastewater

Abstract

As populations shift and grow throughout the world, the amount of organic waste generated directly and indirectly by humans has increased. Wastewater treatment operations play a key role in helping to keep our natural surrounding water bodies clean by removing nitrogen (N), phosphorus (P), and other contaminants of concern from wastewater. Floating treatment wetlands (FTWs) may offer a low-cost energy efficient supplemental treatment option to existing wastewater treatment operations by removing nutrients from wastewater through plant uptake, adsorption, and microbial processes. The purpose of the study was to determine the N and P reduction capabilities of mesocosm FTWs from both domestic and aquaculture wastewater. The extent to which FTW plant species diversity (monoculture vs polyculture) influenced N and P removal was investigated, and the N and P removal dynamics throughout the growing season were characterized. Water samples and plant measurements were collected every week over the course of 14- and 10-week trials during 2022 and 2023, respectively. Mesocosm FTWs were located at the Greenville Utilities Commission Wastewater Treatment Plant for domestic wastewater research and the Marine Aquaculture Research Center of North Carolina State University for aquaculture wastewater research. For both trial 2 studies of the MARC and GUC-WWTP, there were no statistically significant differences among treatments of nitrogen (N) or phosphorus (P) removal. However, for all trials N was removed more effectively than P. The GUC-WWTP had removal ranges of 0.12 to 0.32g/m2/day for N and 0.01 to 0.08 g/m2/day for P. The MARC trial 1 had removal ranges of 0.49 to 0.95 g/m2/day for N and 0.02 to 0.04 g/m2/day for P whereas the trial 2 study has removal ranges of 0.21 to 0.43 g/m2/day for N and 0.004 to 0.02 g/m2/day for P. Overall, the late summer growing season (MARC 1) had higher nitrogen removal rates compared to late spring and early summer (MARC 2). For the GUC-WWTP, there was more phosphorus removed compared to the MARC, for trial 2. Yet all achieved positive removal rates in summation of both locations. The purpose of this study was to characterize the N and P removal efficacies of monoculture vs mixed species plantings of floating treatment wetlands from wastewater. Additional research into native wetland plant species and their nutrient removal potential could aid in finding alternatives or supplements to high energy-dependent treatment methods at wastewater treatment facilities. Future studies should investigate how water hydraulic retention times, continuous flow vs batch systems, and seasonal plant growth characteristics impact nutrient removal efficacies. Other studies into plants with more P removal efficacy and plants with more nutrient specific uptake rates could be effective depending on the nutrients being removed.