The Oxygen Transfer Capacity of Submerged Plant Elodea densa in Wastewater Constructed Wetlands

There are insufficient data for the development of process design criteria for constructed wetlands systems based on submerged plants as a major treatment agent. The aim of the study was to evaluate the oxygen transfer capacity (OTC) of E. densa, in relation to wet plants’ mass (w.m.), and the influence of E. densa on the oxygen concentration and contaminants’ removal efficiency from municipal wastewater. The obtained oxygen concentration and temperature data allowed to calculate the OTC values (mg O2·L−1·h−1), which had been related to wet plants’ mass unit (mg O2·L−1·h−1·g w.m.−1). The efficiency of wastewater treatment was determined in relation to initial wastewater content in the mixture of wastewater and tap water (0%, 25%, 50%, and 100%) during 3 days of the experiment duration. The simulation of day and night conditions was done by artificial lighting. Before and after finishing the second experiment, the COD, Ntotal, and P-PO4 concentration were analyzed in wastewater solutions. The OTC ranged from 3.19 to 8.34 (mgO2·L−1·h−1·g w.m.−1), and the increase of OTC value was related to the increase of wet plant’s mass. The research showed that E. densa affected positively on the wastewater treatment efficiency, and the highest efficiency was achieved in 25% wastewater solution: 43.6% for COD, 52.9% for Ntotal, 14.9% for P-PO4.