Application of QUAL2K model to assess ecological purification technology for a polluted river

Abstract

Industrialization and urbanization have caused water pollution and ecosystem degradation, especially in urban canals and rivers in China; accordingly, effective water quality improvement programs are needed. In this study, the Tianlai River in Jiangsu, China was taken as a research site, and a combination of ecological purification technologies consisting of biological rope, phytoremediation, and activated carbon were applied in a laboratory-scale study to examine degradation coefficients under dynamic water conditions. Coefficients were then input into the QUAL2K model to simulate various hypothetical scenarios and determine the minimum density of ecological purification combination and hydraulic retention time (HRT) to meet Grade V or IV of the China standard for surface water. The minimum densities for Grade V and IV were 1.6 times and 2 times the experimental density, while the minimum HRTs for Grade V and IV were 2.4 day and 3 day. The results of this study should provide a practical and efficient design method for ecological purification programs.

Figure 1

Schematic diagram of the experimental device.

Figure 2

Average nitrogen (a) and phosphorus (b) indexes and their standard deviation along tanks.

Figure 3

Location of the study area and sampling points in the Tianlai River.

Figure 4

Water quality calibration results for the Tianlai River. (a). N indexes; (b). P indexes.

Figure 5

Simulation results of the water quality of Tianlai River under present conditions Simulation of water quality with ecological material at different densities.

Figure 6

Relationship between effluent concentration and ecological material density. The dotted lines indicate Grade V and IV NH₄⁺-N (2 mg/L, 1.5 mg/L), TN (2 mg/L, 1.5 mg/L) and TP (0.4 mg/L, 0.3 mg/L) levels.

Figure 7

Relationship between effluent concentration and HRT. The dotted lines indicate Grade V and IV NH₄⁺-N (2 mg/L, 1.5 mg/L), TN (2 mg/L, 1.5 mg/L) and TP (0.4 mg/L, 0.3 mg/L).