[Purification Effect of Submerged Macrophyte System with Different Plants Combinations and C/N Ratios]

A submerged macrophyte pond can effectively remove nitrogen and phosphorus from water, with the removal efficiencies for pollutants depending on combinations of submerged macrophytes. Moreover, the material structure of sewage also has a significant impact on the purification effect of the submerged macrophyte system. This experiment selected three submerged plants (Vallisneris spiralis, Hydrilla verticillata, and Myriophyllum spicatum) to examine the purification effect of their combinations on sewage, including nitrogen and phosphorus removal efficiencies. In addition, the effect of influent C/N ratio on the submerged macrophyte pond was also tested and discussed. The results showed the following. ① All plant combinations can decrease concentrations of nitrogen and phosphorus in water, resulting from nutrient deposition along with sedimentation of suspended particles. The combinations of Vallisneris spiralis and Hydrilla verticillata showed the highest purification efficiency for total nitrogen and total phosphorus with an average removal rate of 32.71% and 22.13%, respectively. ② The purification effects of three C/N ratio (1.89, 5.93, and 12.09) for Vallisneris spiralis and Hydrilla verticillate system were different. The removal efficiency was highest when the C/N ratio was 5.93, with removal rates for total nitrogen and total phosphorus and a reduction in permanganate index of 81.34%, 68.26%, and 88.65%, respectively. The C/N ratio affected the degradation of nitrogen, phosphorus, and organic matter by influencing the dissolved oxygen concentration of water and changing the anaerobic and aerobic environment of the water. In conclusion, different submerged macrophyte combinations showed better purification effect than a single type of plant in the submerged plant pond system. Changing the influent C/N ratio by placing carbon source materials into the water can greatly increase the removal efficiency of submerged plant pond, providing a practical reference for the use of submerged plant ponds to treat sewage.