Treatment efficiency of different nitrogen-rich wastewater using Lolium perenne L. cultured by nutrient film technique

Plant filters with 0.4×2 m Nutrient Film Technique(NFT) culture grass (Lolium perenne L.) strips were used to treat 26.77 liters five types of nitrogen-rich wastewater which were renewed periodically, every 10 d, marked as G1, G2, G3, G4 and CK. Wastewater G1, G2, G3 and G4 were composed with TAN of 139.6, 139.0, 39.0 and 39.3 mg·L^-1, NO^-₂-N of 40.7, 4.1, 40.4 and 4.1 mg·L^-1, and NO^-₃-N of 75.5, 9.7, 9.5 and 74.7 mg·L^-1, respectively. Wastewater CK group was only with high level NO^-₃-N, 73.9 mg·L^-1. It was found that the greatest removal mass of each nitrogen compound among the first two days of every period was obtained in the group with higher level of that compound and lower level of other two compounds. It took two days for all groups to clean more than 99 percent of un-ionized ammonia and keep pH value between 6.5 and 8.0. With a view of 90 percent absorption of three nitrogen compounds, group G3 and CK only spent two days, shorter than four days of G3, while G1 and G2 failed all period long except for TAN and NO^-₂-N. In terms of grass product achievements at the end of the experiment, group G3 achieved the highest height increase of 169.3 millimeters and the most dry grass yield of 0.205 kg per square meter, and group G4 got the most fresh grass yield of 1.48 kg per square meter.