Study on seasonal floating treatment wetland combination water purification based on numerical simulation

Abstract

The North Canal Basin, Tianjin, section in Wuqing urban area is subject to multi-source pollution from its surroundings and exhibits characteristics of a stagnant water body. As an urban landscape water body, there is immense pressure to improve its water environment and quality. During the 13th Five-Year Plan, China's “Major Special Project for Water Pollution Control and Treatment Technology” conducted research and demonstration of remediation technologies for this river section. Three water quality indexes, ammonia nitrogen (NH3-N), total phosphorus (TP), and chemical oxygen demand (COD) were improved to some extent. In this study, based on the experimental results of the water special project and the achievements of the two-dimensional hydrodynamic water quality model of this river section, nine different Floating Treatment Wetland (FTW) combination schemes were designed for the summer, autumn, and winter without changing the original ratio of FTW in the demonstration project. The scenario simulation results indicate that the optimal FTW combination schemes for the three seasons are A3, B1, and C2, respectively; the water purification effects of each optimal FTW combination scheme are superior to those of the original demonstration project, with the removal rate performance of the optimal scenario simulations for the three seasons being B1 > C2 > A3. Further single-factor evaluation of water quality under the nine FTW combination schemes reveals that each scheme significantly improves the water quality of North Canal Basin in different seasons, with the best removal effect achieved in autumn, reaching Class IV water quality, followed by winter and summer, both achieving Class V water quality. The results of this study can provide guidance for devising aquatic plant arrangements that meet water quality standards in different regions and offer a theoretical basis for the sustainable development of water quality purification in different seasons for northern rivers, taking the example of North Canal Basin.