Combined treatment with pre-aeration and carrier addition strengthens the purification performance of a deep pilot-scale duckweed-based pond

Duckweed has a great potential in phytoremediation due to its rapid growth and high-value biomass. Although single measures, including pre-aeration or carrier addition treatment, have been demonstrated as viable options for duckweed-based ponds (DWPs) enhancement, it remains unknown whether pre-aeration can act synergistically with carrier addition in a deep DWP. Thus, combined treatment with pre-aeration and carrier addition was compared to single treatment with pre-aeration for strengthening the purification performance of a deep pilotscale DWP (8 m2) over a 9-month period in this study. The results showed that both single and combined treatments increased the dissolved oxygen concentration (by 264 % and 243 %, respectively) and oxidationreduction potential (by 33 % and 37 %, respectively) of pond water, while promoting duckweed growth (by 42 % and 45 %, respectively), nutrient (nitrogen and phosphorus) recovery and removal. These treatments also increased the relative contribution of microorganisms to nutrient removal. Due to the synergistic effect of preaeration and carrier addition, combined treatment performed better than single treatment at strengthening the performance of DWPs, which may be attributed to a higher duckweed growth rate supported by abundant plant growth-promoting bacteria (e.g., Herbaspirillum, Brevundimonas, Allorhizobium-Neorhizobium-PararhizobiumRhizobium and Sphingomonas) associated with duckweed, as well as to a greater nutrient removal promoted by functional microorganisms in pond water (e.g., Acinetobacter and Hydrogenophaga) and carrier biofilm (e.g., Pseudomonas, Sulfurovum, and Sulfurimonas). Thus, this study demonstrates the synergistic effect of combined treatment with pre-aeration and carrier addition, and clarifies the roles of duckweed and microorganisms in a deep DWP under combined treatment.