Growing duckweed in swine wastewater for nutrient recovery and biomass production.

Spirodela oligorrhiza, a promising duckweed identified in previous studies, was examined under different cropping conditions for nutrient recovery from swine wastewater and biomass production. To prevent algae bloom during the start-up of a duckweed system, inoculating 60% of the water surface with duckweed fronds was required. In the growing season, the duckweed system was capable of removing 83.7% and 89.4% of total nitrogen (TN) and total phosphorus (TP) respectively from 6% swine lagoon water in eight weeks at a harvest frequency of twice a week. The total biomass harvested was 5.30 times that of the starting amount. In winter, nutrients could still be substantially removed in spite of the limited duckweed growth, which was probably attributed to the improved protein accumulation of duckweed plants and the nutrient uptake by the attached biofilm (algae and bacteria) on duckweed and walls of the system.