Wetland plants like Acorus gramineus, Juncus effusus, and Iris japonica can help clean up sewage water by removing pollutants like COD and nitrogen. The plants were tested in constructed wetlands, and it was found that Acorus gramineus was the most effective at purifying the water, followed by Juncus effusus and Iris japonica. The more plants there were, the better the purification efficiency. So, planting these wetland plants can help make sewage water cleaner by absorbing pollutants and promoting natural processes that clean the water.