Effects of feeding mode on the performance, life span and greenhouse gas emissions of a vertical flow macrophyte assisted vermifilter

Authors: SINGH, RAJNEESH - University Of Minnesota; RAY, CHITTARANJAN - University Of Nebraska; Miller, Daniel; Durso, Lisa; MENESES, YULIE - University Of Nebraska; BARTELT-HUNT, SHANNON - University Of Nebraska; D'ALESSIO, MATTEO - University Of Mississippi

Submitted to: npj Clean Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2022
Publication Date: 7/13/2022
Citation: Singh, R., Ray, C., Miller, D.N., Durso, L.M., Meneses, Y., Bartelt-Hunt, S., D'Alessio, M. 2022. Effects of feeding mode on the performance, life span and greenhouse gas emissions of a vertical flow macrophyte assisted vermifilter. npj Clean Water. https://doi.org/10.1038/s41545-022-00171-4.
DOI: https://doi.org/10.1038/s41545-022-00171-4

Interpretive Summary: Vermifilters are innovative biologically-based wastewater treatment systems that pair soil filtration and earthworms as an economical and sustainable alternative to traditional wastewater treatment. In addition to worms, some vermifilters also include plants (macrophytes) to improve treatment efficiency. Vermifilters have primarily been applied to the treatment of domestic wastewater, however they also have potential to be effective for the treatment of industrial wastewaters. In this study macrophyte assisted vermifilters (MAVFs) were designed to treat slaughterhouse wastewater. The effects of different aeration strategies and two wastewater application timings (8 hours/day and 24 hours/day) were evaluated for performance by measuring chemical oxygen demand (COD), total nitrogen (TN), and total phosphorous (TP) removals; clogging, gaseous emissions, and biomass growth. The 8 hours/day strategy allowed for the diffusion of into the MAVF during no-flow conditions, which improved function as measured by higher organics oxidation, adsorption of phosphorous, nitrification, and ammonification. This intermittent application of influent to MAVFs adds a higher amount of dissolved oxygen to the system, and it can be a milestone in significantly increasing the MAVF based treatment systems' performance, life span, and emission characteristics. However, a cost-benefit analysis and additional experiments to identify the mechanisms behind the impact of intermittent feeding on biomass growth and phosphorous removal are necessary before recommending this strategy to be applied on a larger scale.

Technical Abstract: This study was conducted to investigate the impact of intermittent feeding on performance, clogging, and gaseous emission on macrophyte assisted vermifiltration (MAVF) based treatment system. Slaughterhouse wastewater was applied to two different integrated vertical flow based MAVFs. Triplicates were used throughout the study. Eisenia Fetida earthworms were added to MAVFs, and Carex muskingmenis plants were planted. Wastewater was applied to the reactors on 1) intermittent (8 hours/day) (IMAVF) and 2) continuous (24 hours/day) (CMAVF) basis. The average chemical oxygen demand, total nitrogen, and total phosphorous removals achieved by the IMAVF were 80.2±1.6%, 53.9±1.3% and 66.5±1% respectively, and 68.3±1.3%, 61.2±1.4%, and 60.5±1.4% by the CMAVF, respectively. The diffusion of air to the bedding of IMAVFs during no-flow conditions facilitated higher organics oxidation, adsorption of phosphorous, nitrification, and ammonification. At the end of the study, hydraulic conductivity of IMAVF and CMAVF were found to be 0.036 cm/s and 0.037 cm/s, respectively. CO2, CH4 and N2O emissions from IMAVF were 245.5±38.0 mg C/m2, 5.0±4.6 mg C/m2 and 2513.5±2629.9 mg N/m2 respectively, while CO2, CH4 and N2O emissions from CMAVF were 123.3±14.5 mg C/m2, 74.8±45.2 mg C/m2 and 328.4±93.4 mg N/m2, respectively. Intermittent application of influent could be considered for improving the performance and lifespan of MAVFs, causing lower environmental footprints.