Ecological Engineering Of Water Hyacinth (Eichhornia Crassipes) In The Watershed: Control And Utilization

Water hyacinth (Eichhornia crassipes), introduced into China in 1930's, spreads very quickly in recent years because of water eutrophication in watershed areas. It has become a social problem as it occupies waterway, disturbs aquatic ecosystem equilibrium and impacts local economics.This work follows the basic principles of ecological engineering for the control and utilization of water hyacinth. Firstly, the state-of-the-art growth pattern of water hyacinth was field investigated while the causes of rapid spread of the plant were probed at the laboratory. Based on the study, measures for water hyacinth control were proposed. Secondly, the efficiency of nutrient removals in the eutrophication water by water hyacinth harvest was calculated based on the models of growth and surplus production. Thirdly, anaerobic fermentation of water hyacinth for biogas production was developed for water hyacinth, at both laboratory and pilot scales. Finally, the ecological and economical benefits and sustainability of water hyacinth ecological engineering were assessed by ways of emergy analysis and technical economics analysis.Main findings and results of this study are concluded as follows.(1) Water hyacinth is found mostly in stagnant and eutrophication waters of inner-waterways, channels and ponds. Its populations double as fast as in 8-10 days under favorable conditions. It shows by nutrient-exhausting experiments that water hyacinth may endure the condition of nutrient deficient and that larger plant can grow well without any nutrient supply for one month. The limiting factors of the plant growth are TN and TP, and there is no significant difference for the plant growth between distilled water groups and the experimental groups whose concentration of TN and TP are less than 2.0mg/L and 0.05mg/L respectively. That means TN of 2.0mg/L or TP of 0.05mg/L in the water may be the threshold concentration of rapid spread of the plant.(2) Waste water from livestock could promote the growth rate of water hyacinth remarkably. The plants double in 6-7 days in livestock waste water with moderate concentrations. Meanwhile, the plant has significant purification ability. For example, the removal rates of COD, TN and TP in 25 days may reach 60%-88%, 50%-90%, and 50%-60%, respectively. The purification rate of water hyacinth for moderate...