Removal of Agricultural Non-Point Source Pollutants by Artificial Aquatic Food Web System: A Study Case of the Control of Cynobacterial Bloom in Jiyu River

Abstract

An artificial aquatic food web (AAFW) system was designed to remove the non-point source pollutants in eutrophic Jiyu river. A certain amount of Scenedesmus obliquus and Daphnia pulex was cultured in the system for the control of serious cyanobacterial bloom. The AAFW system was a continuous-flow system including one storage basin of 3 m 3 capacity with polluted river water (the total nitrogen-TN: 4.49 mg ⋅l -1 ; the total phosphorus-TP: 0.192 mg ⋅l -1 ), one phytoplankton tank of 3 m 3 capacity with an initial concentrations of S. obliquus about 5.8 × 10 3 ind ⋅l -1 , and one zooplankton growth chamber of 1.5 m 3 capacity with an initial abundance of D. pulex about 22.5 ind ⋅l -1 . The system was optimized by setting hydraulic retention time of phytoplankton tank as 5 days and the experiments were operated for 45 days. Compared with the polluted river, TN and TP were removed about 28% and 47% by the AAFW system, respectively. The biomass of phytoplankton decrease from 6.33 mg ⋅l-1 to 1.48 mg ⋅l-1 and the percentage of cyanobacteria decrease from 43.93% to 2.36%, the biomass of Crustacean zooplankton increase from 0.34 mg ⋅l -1 to 1.53 mg ⋅l -1 and the percentage of D. pulex increase from 19.19% to 57.62%. Our results indicated that the AAFW system not only is an efficient, flexible system for reducing nutrient levels in tributary rivers, but also has an ability to control the cyanobacteria bloom and rebuilding the aquatic ecosystem from the polluted river water.