The Research On Ecological Engineering Of Constructed Wetlands In The Treatment Of Wastewater From The Duck Farm

Nowadays intensive breeding of poultry and livestock at large scale had rendered the treatment of its waste and wastewater an urgent environmental issue, which motivated this study. A wetland of 688 m² was constructed on a duck farm, and water hyacinth (Eichhornia crassipes) was chosen as an aquatic plant of the wetland from September to November in 2005, while yellowflag iris (Iris pseudacorus L.) was selected and cultivated from March to May next year. At the same time water hyacinth was utilized as succulence for duck production. The objective of this study was to observe water hyacinth's role in purifying the rich wastewater and its effects on the duck feed intake, duck egg laying performance and duck egg quality, also to observe yellowflag iris's cold and pollution resistance and purifying abilities. The results showed that the water hyacinth constructed wetland removed as high as 64.44% of chemical oxygen demand (COD), 21.78% and 23.02% of total nitrogen (TN) and total phosphorus (TP) respectively. Both dissolved oxygen (DO) and water transparency of the wastewater were remarkably improved, with the transparency being 2.5 times higher than that of the untreated. The research also showed that yellowflag iris could well survival and grow about 7℃, and after 70 days, the ramet number and the mean height increased 42.10% and 314.98%, respectively. Based on its strong pollution resistance and purifying abilities, the removal rates of COD, TP, TN and NH₄-N achieved 13.34%, 49.43%, 22.15% and 66.46%, respectively. At the same time, ecological benefits of beautifying environment and economical benefits by selling it as garden flower were both gained. After the egg ducks were fed by water hyacinth as its succulence, the average daily feed intake and the egg laying ratio in the testing group were 5.86% and 9.79% higher than that in the control group respectively, the differences between tested group and control group were both significant at 0.01 probability level. The egg weight in the testing group was 2.36% higher than that inthe control group (P<0.05 ), but the feed conversion ratios were almost the same. Theeggshell thickness and the eggshell intention among egg qualities significantly increased in ducks feed with water hyacinth. At last we concluded that a water hyacinth system had effective capacity on purification wastewater from intensive duck farm during the water hyacinth growth season, while yellowflag iris was a preferable plant for constructed wetlands at the Tai Lake Basin in spring and winter. After harvested, water hyacinth had excellent performance as duck succulence. At last, effects of the wastewater treatment was analyzed, and compared with national standard. Several indexes achieved demands of discharge standard of pollutants for municipal wastewater treatment plant (GB 18918-2002) , for example COD and TN. Some indexes reached demands of environmental quality standards for surface water (GB 3838—2002) . Based on these, multilevel treatments of wastewater from intensive duck farms were suggested, namely the first step (water hyacinth, Yellowflag iris and so on as the main plants), the second step (fish ponds), the third step (hydrophytic economy plants) and the forth step (rice paddy).