Decontaminate Effect of Paddy Field on Waste Water from Fish Pond under Different Residence Time

Wastewater from aquiculture contains useful nutrients for plant, such as nitrogen and phosphorus. Drainage of the wastewater resulted in eutrophication of water body. The nutrients in wastewater from fish pond was assimilated and utilized by paddy field. Using test-pits with a relatively independent irrigation-drainage system, an experiment was carried out that paddy field was used for decontaminating waste water from fish pond, the decontaminate effect were studied under three residence time (2d, 4d and 6d) of wastewater in paddy field and in three growing stage of paddy (booting stage, heading stage and yellow ripe stage). The results showed: (1)ÙWithin 7 days of application of basal fertilizer and tillering fertilizer, nitrogen(N) and phosphorus (P) concentrations in surface water of paddy field were higher and reduced rapidly, after 7 days, N and P concentrations stabilize. (2)Ú The paddy fields have a significant decontaminate effect on wastewater from fish pond under the three residence time and three growing stage of paddy, the more of the detention time the better of water purification effect, but decontaminate efficiency declined gradually with increase of wastewater residence time in three growing period of paddy. In booting stage of paddy, the removal rate of total phosphorus (TP) were higher than that of the others, but the removal rate of total nitrogen (TN) were lower than that of the others, In heading stage, the removal rate of TN and NH₃^-N were higher than that of the others, In yellow ripe stage, the removal rate of NO₃^--N were higher than that of the others. The results indicated: (1)ÙIn order to avoid nutrient loss of paddy field and water body pollution, drainage experiments of paddy field used for decontaminate waster water from fish pond were not suitable after fertilization. (2)Ú Base on the comprehensive consideration of removal rate", "removal efficiency and ir- igation energy saving, there modes were propitious to decontaminate of wastewater from fish pond: the wastewater of fish pond were retained in paddy field for 6d in booting stage of paddy, for 4d in heading stage and for 2d in yellow ripe stage of paddy respectively.