Studies On Effects Of Duckweed On Removal Of Nitrogen And Phosphorus From Polluted Water Bodies

With the development of economic and the growth of population, the amount of wastewater rich in nitrogen and phosphorus caused by intensive livestock farms and urban waste is increasing. Since water quality management and sewage treatment is falling far behind, eutrophic water has increased significantly and deterioration of water environment is becoming a serious problem. The key technical problem waiting to be solved is to clean and repair water bodies economically and efficiently. The most effective and easy promoting technology to use aquatic plants for purifying wastewater containing nitrogen and phosphorus.In this paper, Yangzhou local duckweeds are used to study the growth capacity of and tolerance of duckweeds to nitrogen and phosphate in water. Duckweed species with high growth rate and high nitrogen and phosphorus removal rate were selected. Effects of environmental conditions on the growth of duckweeds and nitrogen and phosphorus removal efficiency was investigated. Purification effect of duckweeds on breeding wastewater and eutrophic water in indoor stagnant water treatment. This is expected to provide a useful reference for further research and application. The major findings are as follows:1, Local Lemna aequinoctialis, Spirodeta oligorrhiza and Spirodela polyrrhiza grew well in the medium. These three duckweed species all grew better in Hoagland medium than in Hutner medium. And Lemna aequinoctialis could have the highest relative growth rate of 0.236. When cultivated in Hutner medium, Spirodela polyrrhiza had symptoms of uprooting, loss of green, bleached etc, which indicated an unhealthy growth. Therefore, Lemna aequinoctialis and Spirodeta oligorrhiza which have stronger tolerance could be considered for follow-up research objects.2, Under different pH, density, temperature and other environmental conditions, Lemna aequinoctialis's showed higher relative growth rate and efficiency of removing nitrogen and phosphorus from Hoagland medium than Spirodeta oligorrhiza. Generally, the optimal growth condition for Lemna aequinoctialis is at pH 6.0, density 60%(salvage cycle is 12 days) and temperature 25℃. This is also condition when Lemna aequinoctialis had the higest removal efficiency.3, Nitrogen and phosphorus removal efficiency to diluted anaerobic dairy wastewater of Lemna aequinoctialis is stronger than that of Spirodeta oligorrhiza, with the removing rate of total nitrogen and phosphorus achieved 74.92%and 88.00%, respectively.4, The growth rate of Spirodeta oligorrhiza is lower than Lemna aequinoctialis, as well as nitrogen and phosphorus removal efficiency to natural waterbodies.Certain duckweed species has great tolerance and removal capability of N and P. They could be used in bioremediation of eutrophicated water body and other natural water bodies, as well as in the post treatment of wasteater rich in N and P, such as domestic sewage, breeding wastewater ect. Duckweed has a high growth rate and strong absorption to N and P, and it is easy to harvest and remove. To harvest regularly can keep duckweed population at a high growth rate, therefore the duckweed-based purifying system can work steadily. As duckweed is rich in nutrients, it can be used to feed fishes, pigs, ruminants and chicken. Moreover, it can be used as ecological fertilizers and materials for biogas. Developing the sewage purification capacity of duckweed and comprehensive utilization, duckweed-based technology can improve the sustainable development of fish culture, Stockbreeding and ecological agriculture greatly.