Utilization of nutrient film technology grass to treat wastewater from a recirculating aquaculture system

To investigate the feasibility of applying plant eco-filtration method in recirculating aquaculture systems, four 3.0 m?0.5 m?0.05 m （L ? W ? H） plant filters were used to provide 4 replicates for treatment of wastewater from a Colossoma brachypomum intensive system. 0.8m^2 NFT （nutrient film technology） Lolium perenne was planted on each filter. Wastewater was loaded at a rate of 25.4 liter per week for an investigation of 40 day. After a recirculating irrigation of 7 days, the plant filer removed 96.1% of nitrate nitrogen, 86.2% of total nitrogen, 90.5% of total phosphorus, and 88.7% of COD, respectively, pH was raised from 6.4 to 8.4 and only 29.7 % of water was used. All parameters conformed to qualifications of China water quality standard for fisheries except unionized ammonia nitrogen as a result of high pH. The grass height increased at a rate of 2.3 mm?d^-1, significantly slower than that irrigated with commercial nutrient solution with a growth of 13.2mm?d^-1. Total ammonia nitrogen and nitrate nitrogen concentration of the fresh grass leaves were 107.9 and 42.5μg?g^-1, respectively. At the end of this experiment, 582.9 g?m^-2 fresh grass was produced and then was turned over to 102.5 g?m^-2 dry mass with a dry weight to fresh weight ratio of 0.176. It can be concluded that the plant filter is an environment-friendly way to solve accumulation of N, P, and COD, and descent of pH in recirculating aquaculture systems. With a view to healthy growth of grass, it＇s recommended that grass in plant filters should be periodically returned to breeding systems for a certain term irrigation of commercial nutrient solutions.