Nitrogen Removal in Duckweed-Based Ponds with Effluent Recirculation

Abstract

A pilot-scale set of duckweed-based ponds (DWBPs) were set up with effluent recirculation added into the influent line to see what effect this had on solving system failure and enhancing nitrogen removal. The experimental results showed that the optimum performance in terms of nitrogen removal was obtained when the system was operated at a hydraulic retention time (HRT) of 16 days with 100% effluent recirculation. Average removal efficiencies were 72% for total nitrogen (TN), 72% for total kjeldahl nitrogen (TKN) and 73% for ammonia-nitrogen (NH₄-N). During the six-month study period, it was found that all the experimental systems had good stability with no die-off of the duckweed. A nitrogen mass balance study indicated that the three main mechanisms for nitrogen removal in the DWBPs with effluent recirculation were; duckweed uptake, nitrification-denitrification and sedimentation, respectively. The first order constant rates () for TN removal and for NH₄-N were in the range of 0.048-0.074 and 0.047-0.78 per day, respectively.