Study on the purification ability of 29 aquatic plants to rural domestic sewage

In order to screen aquatic plants for the effective purification of rural retail sewage water, 29 common aquatic plants were tested to compare their removal capacity for total nitrogen (TN), ammonia nitrogen (NH3-N), total phosphorus (TP), chemical oxygen demand (CODCr), and suspended solid (SS)in a septic tank effluent system. The removal ability of different plants on pollutants was determined and clustering analysis was conducted. The results showed that the removal rate of pollutants in control without plant was significantly lower than that of plant treatment. Treatment time significantly affected the purification efficiency of all pollutants. In the early stage of the experiment, the purification rate of pollutants by aquatic plants was fast. At the end of the 75-day experiment, the purification rate of TN was 6.21%~26.66% higher than that of the non-plant control, the purification rate of NH3-N, TP, CODCr, and SS was increased by 7.03%~23.92%, 17.40%~28.13%, 7.47%~18.62%, and 8.90%~13.00%, respectively. Eichhornia crassipes had certain advantages in the purification rate of TN, NH3-N, and TP in the early stage of experiment, indicating that the purification of these pollutants was obviously affected by Eichhornia crassipes in a short period of time. However, the purifying ability of Eichhornia crassipes in the late stage of the experiment was similar to that of other plants. Phragmites australis and Typha orientials had better TP purification effects in the later experiment. According to the average subordinate function value of screening index, 29 species of plants were clustered and classified into three categories:high purifying ability plants including Phragmites australis, Eichhornia crassipes, Typha orientials, Arundo donax, and Canna indica; medium purifying ability plants such as Cyperus alternifolius, Zantedeschia aethiopica, Pistia stratiotes, Nymphaea L., Salvinia natans, Elodea nuttallii, Azolla imbricata, Scirpus validus, Vallisneria natans, Acorus calamus, Ceratophyllum demersum, Lythrum salicaria, Nelumbo nucifera, Nuphar pumilum, Pontederia cordata, Zizania caduciflora, Myriophyllum verticillatum, Thalia dealbata, Potamogeton crispus, Hydrilla verticillata, Iris germanica, Euryale ferox, and Iris pseudacorus; and low purifying ability species Trapa bispinosa. Results showed that emerged plant (Phragmites australis, Typha orientalis, Arundo donax, Canna indica), floating-leaved plant (Nymphaea L.), floating plant (Eichhornia crassipes), and submerged plant (Elodea nuttallii and Vallisneria natans)were suitable for phytoremediation and treatment of rural domestic sewage. Eichhornia crassipes was an invasive alien species, certain control measures need to be taken to prevent damage to the original ecosystem in engineering application.