Abstract: With diluted anaerobically pretreated wastewater from a pig farm and Spirodela oligorrhiza,TN,NH⁺₄-N and NO^-_x-N removal pathways in shallow-water duckweed-based wastewater treatment systems were studied in summer and winter.Results show that,in summer,30.5% of the TN was removed through ammonia volatilization and 15.9% and 53.6% of NH⁺₄N and NO^-_x-N through duckweed uptake/adsorption,respectively,and 33.1%,17.3% and 49.6% of NH⁺₄-N through ammonia volatilization,duckweed uptake/adsorption and nitrification,respectively,and duckweed uptake/adsorption was the only pathway for removal of NO^-_x-N.While in winter,31.7% and 68.3% of the TN was removed through ammonia volatilization and NH⁺₄-N uptake/adsorption by duckweeds,respectively,28.9%,69.5% and 1.6% of the NH⁺₄-N through ammonia volatilization,duckweed uptake/adsorption and nitrification,respectively,and the content of NO^-_x-N,however,remained unchanged.

Key words: duckweed, wastewater treatment, shallow-water, nitrogen, removal pathway