Purification efficiency of nitrogen and phosphorus in Ottelia acuminata on four kinds of simulated sewage

• O. acuminata can survive concentration of TN over 5.5 mg/L.
• O. acuminata has relatively high removal efficiency for nutrients in some sewage.
• O. acuminata can be used in constructed wetlands to purify farmland runoff.
• The optimal HRT of O. acuminate-dominated constructed wetlands was about 4 days.

Erhai Lake is mainly composed of low-pollution river water, farmland return water, village farmland mixed sewage, and village ditch water. The study of whether Ottelia can adapt to these four types of sewage and clean the water not only can clarify the resistance of Ottelia to contamination but also has good application value. Ottelia was experimentally cultivated in simulated sewage through artificial water distribution according to the characteristics of nitrogen and phosphorus in the four kinds of sewage. The changes in the nitrogen and phosphorus contents in water and Ottelia were determined. The adaptation of Ottelia to these four kinds of sewage, as well as the nitrogen and phosphorus purification efficiencies, was studied. Results showed that Ottelia could survive in simulated farmland return water, low-pollution river water (Yongan River) and village farmland mixed sewage. The nutrients in water influenced the flowering behavior of Ottelia. The maximum average total phosphorus and ammonia nitrogen removal rates of 29.88% and 32.4%, respectively, in Ottelia were found in the low-pollution river group. The average total nitrogen removal rate in the farmland return water group was the highest at 31.29%. Considering the removal rate, total removed volume, and Ottelia growth, the efficiency of applying Ottelia in the treatment of farmland return water around Erhai Lake was the highest. Moreover, the optimal hydraulic retention time should be 4 days when Ottelia is applied for the treatment of farmland return water from constructed wetlands.