Effect of Plants Combination in Purifying Farmland Drainage

Drainage from farmland contains a lot of nitrogen and phosphorus, it is one of the important causes of water eutrophication. In order to reduce the concentration of nutrients before it discharged into receiving waters, 7 aquatic plants were selected to plant in outdoor planting box in the experiment, 5 different aquatic plant combinations were constructed, the removal effect of different combination was studied under same conditions, the reduction rule was researched, and the nitrogen and phosphorus in sediment were investigated. The results showed: after 49 days, the purifying effect of aquatic plants was significantly higher than that with no plant. Among them, the combination with Lythrum salicaria, Reed, Canna has the best effect in TN and TP removal, the removal rate reach: 90.98%, 95.95%, 98.46% respectively. Reductive process of total nitrogen, ammonia nitrogen and total phosphorus in water are accord with polynomial regression, the concentration decreased along with time increasing. When initial nitrogen and phosphorus content in sediment is higher, nitrogen and phosphorus in the sediment will decrease because of plants absorbing; whereas the initial sediment nitrogen and phosphorus content is low, nitrogen and phosphorus in the water can transfer into the sediment, at the same time, the water was purified.