Oxygen Transport through Aquatic Macrophytes: The Role in Wastewater Treatment

TLDR: In this paper, the effectiveness of three floating and six emergent aquatic macrophytes in improving domestic wastewater quality, based on their capacities for oxygen transport into the rooting zone of the plants created an oxidized microenvironment, thereby stimulating C and N transformations critical to wastewater treatment.

Abstract: Laboratory experiments were conducted to determine the effectiveness of three floating and six emergent aquatic macrophytes in improving domestic wastewater quality, based on their capacities for O₂ transport into the effluent Oxygen transport into the rooting zone of the plants created an oxidized microenvironment, thereby stimulating C and N transformations critical to wastewater treatment Plants were cultured in flasks containing deoxygenated primary and secondary sewage effluent for an 8-d period Oxygen transport by the plants was measured in terms of both O₂ consumed by the effluent (biological O₂ demand reduction—BOD₅) and increased effluent dissolved O₂ Two floating plants, pennywort (Hydrocotyle umbellata L) and waterhyacinth [Eichhornia crassipes (Mart) Solms], and the emergent plants pickerelweed (Pontederia cordata L) and common arrowhead (Sagittaria latifolia L), were superior in improving primary sewage effluent quality, by reducing BOD₅ up to 88%, NH₄-N up to 77%, and increasing dissolved O₂ up to 61 mg L⁻¹ Nitrification rates in pennywort- and water hyacinth-based water treatment systems were calculated to be in the range of 12 to 47 kg NH₄-N ha⁻¹ d⁻¹ Oxygen transport through plants accounted for up to 90% of the total O₂ transported into the effluent In separate batch experiments, the effectiveness of diffuse mechanical aeration (5 and 50 mL air min⁻¹) and of biological aeration (O₂ transport by selected plants including pennywort, waterhyacinth, pickerelweed, and common arrowhead) on the rate of contaminant removal from deoxygenated primary sewage effluent were compared for a 26-d period Biological and mechanical aeration effected similar BOD₅ removal First-order reaction rate constants for BOD₅ removal were from 00066 to 00079 h⁻¹ and from 00041 to 00051 h⁻¹ for biological and mechanical aeration, respectively Rate constants for NH₄-N removal were from 00024 to 00107 h⁻¹ for the plant treatments Virtually complete BOD₅ removal occurred in biological and mechanical aeration treatments within 20 d Complete nitrification of NH₄-N had occurred within 12 d after mechanical aeration was initiated, but subsequent N-loss by denitrification was inhibited In the biological aeration treatments, negligible effluent (NO₃ + NO₂)-N levels were measured, but 65 to 100% NH₄-N loss occurred both by plant assimilation and by sequential nitrification-denitrification reactions Florida Agric Exp Stn Journal Series R-00084