plants die, their decomposition consumes oxygen, which counteracts the reduction of COD, so the water hyacinths should be harvested regularly. In this experiment, the harvested water hyacinths were used to feed ducks, thus completingarecyclingprocess.Fig.4alsoshowstheCOD in the duck pond. There is no significant change of COD during the experimental period, with its value remaining near 250 mg/L. The statistical analysis found that the Fvaluewas40.77,whichmeantasignificantCODdifference (at the 0.01 level) between the water in the CW and the pond (CK)